8th Grade Physical Science Textbook.pdf - Tuscaloosa County ...

ii

Contributing AuthorsChristie Borgford, Ph.D.Professor of ChemistryUniversity of AlabamaBirmingham, Alabama

Andrew ChampagneFormer Physics TeacherAshland High SchoolAshland, Massachusetts

Mapi Cuevas, Ph.D.Professor of ChemistrySanta Fe Community CollegeGainesville, Florida

Leila DumasFormer Physics TeacherLBJ Science AcademyAustin, Texas

William G. Lamb, Ph.D.Science Teacher and Dept. ChairOregon Episcopal SchoolPortland, Oregon

Sally Ann Vonderbrink,Ph.D.

Chemistry TeacherSt. Xavier High SchoolCincinnati, Ohio

Lab WritersPhillip G. BunceFormer Physics TeacherBowie High SchoolAustin, Texas

Kenneth E. CreeseScience TeacherWhite Mountain Junior High

SchoolRock Springs, Wyoming

William G. Lamb, Ph.D.Science Teacher and Dept. ChairOregon Episcopal SchoolPortland, Oregon

Alyson MikeScience TeacherEast Valley Middle SchoolEast Helena, Montana

Joseph W. PriceScience Teacher and Dept. ChairH. M. Browne Junior High

SchoolWashington, D.C.

Denice Lee SandefurScience Teacher and Dept. ChairNucla High SchoolNucla, Colorado

John SpadafinoMathematics and Physics

TeacherHackensack High SchoolHackensack, New Jersey

Walter WoolbaughScience TeacherManhattan Junior High SchoolManhattan, Montana

Academic ReviewersPaul R. Berman, Ph.D.Professor of PhysicsUniversity of MichiganAnn Arbor, Michigan

Russell M. Brengelman,Ph.D.

Professor of PhysicsMorehead State UniversityMorehead, Kentucky

John A. Brockhaus, Ph.D.Director, Mapping, Charting and

Geodesy ProgramDepartment of Geography and

Environmental EngineeringUnited States Military AcademyWest Point, New York

Walter Bron, Ph.D.Professor of PhysicsUniversity of CaliforniaIrvine, California

Andrew J. Davis, Ph.D.Manager, ACE Science CenterDepartment of PhysicsCalifornia Institute of

TechnologyPasadena, California

Peter E. Demmin, Ed.D.Former Science Teacher and

Department ChairAmherst Central High SchoolAmherst, New York

Roger Falcone, Ph.D.Professor of Physics and

Department ChairUniversity of CaliforniaBerkeley, California

Cassandra A. Fraser, Ph.D.Assistant Professor of ChemistryUniversity of VirginiaCharlottesville, Virginia

L. John Gagliardi, Ph.D.Associate Professor of Physics

and Department ChairRutgers UniversityCamden, New Jersey

Gabriele F. Giuliani, Ph.D.Professor of PhysicsPurdue UniversityWest Lafayette, Indiana

Roy W. Hann, Jr., Ph.D.Professor of Civil EngineeringTexas A&M UniversityCollege Station, Texas

John L. Hubisz, Ph.D.Professor of PhysicsNorth Carolina State

UniversityRaleigh, North Carolina

Samuel P. Kounaves, Ph.D.Professor of ChemistryTufts UniversityMedford, Massachusetts

Acknowledgments

Copyright © 2004 by Holt, Rinehart and Winston

All rights reserved. No part of this publication may be reproduced ortransmitted in any form or by any means, electronic or mechanical, includingphotocopy, recording, or any information storage and retrieval system,without permission in writing from the publisher.

Requests for permission to make copies of any part of the work should bemailed to the following address: Permissions Department, Holt, Rinehart andWinston, 10801 N. MoPac Expressway, Building 3, Austin, Texas 78759.

SciLinks is owned and provided by the National Science Teachers Association.All rights reserved.

The name of the Smithsonian Institution and sunburst logo are registeredtrademarks of the Smithsonian Institution. The copyright in the Smithsonianwebsite and Smithsonian website pages is owned by the SmithsonianInstitution.

Printed in the United States of AmericaISBN 0-03-073168-21 2 3 4 5 6 7 048 06 05 04 03 02


iii

Karol Lang, Ph.D.Associate Professor of PhysicsThe University of TexasAustin, Texas

Gloria Langer, Ph.D.Professor of PhysicsUniversity of ColoradoBoulder, Colorado

Phillip LaRoeProfessorHelena College of TechnologyHelena, Montana

Joseph A. McClure, Ph.D.Associate Professor of PhysicsGeorgetown UniversityWashington, D.C.

LaMoine L. Motz, Ph.D.Coordinator of Science EducationDepartment of Learning

ServicesOakland County SchoolsWaterford, Michigan

R. Thomas Myers, Ph.D.Professor of Chemistry, EmeritusKent State UniversityKent, Ohio

Hillary Clement Olson,Ph.D.

Research AssociateInstitute for GeophysicsThe University of TexasAustin, Texas

David P. Richardson, Ph.D.Professor of ChemistryThompson Chemical

LaboratoryWilliams CollegeWilliamstown, Massachusetts

John Rigden, Ph.D.Director of Special ProjectsAmerican Institute of PhysicsColchester, Vermont

Peter Sheridan, Ph.D.Professor of ChemistryColgate UniversityHamilton, New York

Vederaman Sriraman,Ph.D.

Associate Professor of TechnologySouthwest Texas State

UniversitySan Marcos, Texas

Jack B. Swift, Ph.D.Professor of PhysicsThe University of Texas Austin, Texas

Atiq Syed, Ph.D.Master Instructor of Mathematics

and ScienceTexas State Technical CollegeHarlingen, Texas

Leonard Taylor, Ph.D.Professor EmeritusDepartment of Electrical

EngineeringUniversity of MarylandCollege Park, Maryland

Virginia L. Trimble, Ph.D.Professor of Physics and

AstronomyUniversity of CaliforniaIrvine, California

Martin VanDyke, Ph.D.Professor of Chemistry EmeritusFront Range Community

CollegeWestminster, Colorado

Gabriela Waschewsky,Ph.D.

Science and Math TeacherEmery High SchoolEmeryville, California

Safety ReviewerJack A. Gerlovich, Ph.D.Associate ProfessorSchool of EducationDrake UniversityDes Moines, Iowa

Teacher ReviewersBarry L. BishopScience Teacher and Dept. ChairSan Rafael Junior High SchoolFerron, Utah

Paul BoyleScience TeacherPerry Heights Middle SchoolEvansville, Indiana

Kenneth CreeseScience TeacherWhite Mountain Junior High

SchoolRock Springs, Wyoming

Vicky FarlandScience Teacher and Dept. Chair Centennial Middle SchoolYuma, Arizona

Rebecca FergusonScience TeacherNorth Ridge Middle SchoolNorth Richland Hills, Texas

Laura FleetScience TeacherAlice B. Landrum Middle

SchoolPonte Vedra Beach, Florida

Jennifer FordScience Teacher and Dept. Chair North Ridge Middle SchoolNorth Richland Hills, Texas

Susan GormanScience TeacherNorth Ridge Middle SchoolNorth Richland Hills, Texas

C. John GravesScience TeacherMonforton Middle SchoolBozeman, Montana

Dennis HansonScience Teacher and Dept. Chair Big Bear Middle SchoolBig Bear Lake, California

David A. HarrisScience Teacher and Dept. Chair The Thacher SchoolOjai, California

Norman E. HolcombScience TeacherMarion Local SchoolsMaria Stein, Ohio

Kenneth J. HornScience Teacher and Dept. Chair Fallston Middle SchoolFallston, Maryland

Tracy JahnScience TeacherBerkshire Junior-Senior High

SchoolCanaan, New York

Kerry A. JohnsonScience TeacherIsbell Middle SchoolSanta Paula, California

Drew E. KirianScience TeacherSolon Middle SchoolSolon, Ohio

Harriet KnopsScience Teacher and Dept. Chair Rolling Hills Middle SchoolEl Dorado, California

Scott Mandel, Ph.D.Director and Educational

ConsultantTeachers Helping TeachersLos Angeles, California

Thomas ManerchiaFormer Science TeacherArchmere AcademyClaymont, Delaware

Edith McAlanisScience Teacher and Dept. Chair Socorro Middle SchoolEl Paso, Texas

Kevin McCurdy, Ph.D.Science TeacherElmwood Junior High SchoolRogers, Arkansas

Alyson MikeScience TeacherEast Valley Middle SchoolEast Helena, Montana

Donna NorwoodScience Teacher and Dept. Chair Monroe Middle SchoolCharlotte, North Carolina

Joseph W. PriceScience Teacher and Dept. Chair H. M. Browne Junior High

SchoolWashington, D.C.

Terry J. RakesScience TeacherElmwood Junior High SchoolRogers, Arkansas

Beth RichardsScience TeacherNorth Middle SchoolCrystal Lake, Illinois

Elizabeth J. RustadScience TeacherCrane Middle SchoolYuma, Arizona

Acknowledgments (cont.)


iv

Editorial Robert W. Todd, Associate

Director, Secondary ScienceDebbie Starr, Managing EditorAnne Engelking, Senior EditorMichael Mazza, Editor

ANNOTATED TEACHER’S EDITION

Ken Shepardson, Amy James,Michael Mazza, Kelly Rizk, Bill Burnside

COPYEDITORS

Dawn Spinozza, Copyediting Manager

EDITORIAL SUPPORT STAFF

Jeanne Graham, Mary Helbling,Kenneth G. Raymond, Tanu’eWhite

EDITORIAL PERMISSIONS

Cathy Paré, Permissions ManagerJan Harrington, Permissions

Editor

Art, Design, and PhotoBOOK DESIGN

Richard Metzger, Design DirectorMarc Cooper, Senior DesignerRon Bowdoin, DesignerDavid Hernandez, DesignerAlicia Sullivan, Designer (ATE),Cristina Bowerman, DesignAssociate (ATE)

IMAGE ACQUISITIONS

Elaine Tate, Art Buyer SupervisorSean Moynihan, Art BuyerTim Taylor, Photo Research

SupervisorStephanie Morris, Assistant

Photo Researcher

PHOTO STUDIO

Sam Dudgeon, Senior Staff Photographer

Victoria Smith, Photo SpecialistLauren Eischen, Photo

Coordinator

ProductionMimi Stockdell, Senior

Production ManagerAdriana Bardin Prestwood,

Senior Production CoordinatorBeth Sample, Production

CoordinatorSuzanne Brooks, Sara Carroll-Downs

Staff Credits

Rodney A. SandefurScience TeacherNaturita Middle SchoolNaturita, Colorado

Helen SchillerScience TeacherNorthwood Middle SchoolTaylors, South Carolina

Bert J. SherwoodScience TeacherSocorro Middle SchoolEl Paso, Texas

Patricia McFarlane SotoScience Teacher and Dept. Chair G. W. Carver Middle SchoolMiami, Florida

David M. SparksScience TeacherRedwater Junior High SchoolRedwater, Texas

Larry TackettScience Teacher and Dept. Chair Andrew Jackson Middle SchoolCross Lanes, West Virginia

Elsie N. WaynesScience Teacher and Dept. Chair R. H. Terrell Junior High SchoolWashington, D.C.

Sharon L. WoolfScience TeacherLangston Hughes Middle

SchoolReston, Virginia

Alexis S. WrightMiddle School Science

CoordinatorRye Country Day SchoolRye, New York

Lee YassinskiScience TeacherSun Valley Middle SchoolSun Valley, California

John ZamboScience TeacherElizabeth Ustach Middle SchoolModesto, California

Acknowledgments (cont.)


Unit 1 Introduction to Matter 2Chapter 1 The World of Physical Science . . . . . . . . . 04Chapter 2 The Properties of Matter . . . . . . . . . . . . . . 34Chapter 3 States of Matter . . . . . . . . . . . . . . . . . . . . 58Chapter 4 Elements, Compounds, and Mixtures . . . . 80

Unit 2 Motion and Forces 104Chapter 5 Matter in Motion . . . . . . . . . . . . . . . . . . 106Chapter 6 Forces in Motion. . . . . . . . . . . . . . . . . . . 136Chapter 7 Forces in Fluids. . . . . . . . . . . . . . . . . . . . 160

Unit 3 Work, Machines, and Energy 184Chapter 8 Work and Machines . . . . . . . . . . . . . . . . 186Chapter 9 Energy and Energy Resources . . . . . . . . . 212Chapter 10 Heat and Heat Technology . . . . . . . . . . . 244

Unit 4 The Atom 276Chapter 11 Introduction to Atoms . . . . . . . . . . . . . . 278Chapter 12 The Periodic Table . . . . . . . . . . . . . . . . . 300

Unit 5 Interactions of Matter 324Chapter 13 Chemical Bonding . . . . . . . . . . . . . . . . . 326Chapter 14 Chemical Reactions. . . . . . . . . . . . . . . . . 348Chapter 15 Chemical Compounds . . . . . . . . . . . . . . . 372Chapter 16 Atomic Energy . . . . . . . . . . . . . . . . . . . . 396

Unit 6 Electricity 418Chapter 17 Introduction to Electricity. . . . . . . . . . . . 420Chapter 18 Electromagnetism . . . . . . . . . . . . . . . . . . 452Chapter 19 Electronic Technology. . . . . . . . . . . . . . . 480

Unit 7 Waves, Sound, and Light 506Chapter 20 The Energy of Waves . . . . . . . . . . . . . . . 508Chapter 21 The Nature of Sound. . . . . . . . . . . . . . . . 532Chapter 22 The Nature of Light . . . . . . . . . . . . . . . . 562Chapter 23 Light and Our World . . . . . . . . . . . . . . . 592

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 620

Contents v

Contents in Brief


Contents

The World of Physical Science . . . . . . . . . . . . . . 4

Section 1 Exploring Physical Science . . . . . . . . . . . . . 6

Section 2 Using the Scientific Method . . . . . . . . . . . 11

Section 3 Using Models in Physical Science . . . . . . . 20

Section 4 Measurement and Safety in Physical Science . 24

Chapter Highlights/Review . . . . . . . . . . . . . . . . . . . 28

Feature ArticlesCareers: Electronics Engineer . . . . . . . . . . . . . . . . . 32

Science Fiction: “Inspiration” . . . . . . . . . . . . . . . . . . 33

Safety First! 622 Exploring the Unseen 626 Off to the Races! 627 Measuring Liquid Volume 628 Coin Operated 629

The Properties of Matter . . . . . . . . . . . . . . . . . . 34

Section 1 What Is Matter? . . . . . . . . . . . . . . . . . . . . 36

Section 2 Describing Matter . . . . . . . . . . . . . . . . . . 43

Chapter Highlights/Review . . . . . . . . . . . . . . . . . . 52

Feature ArticlesAcross the Sciences: In the Dark About Dark Matter . 56

Health Watch: Building a Better Body . . . . . . . . . . . . 57

Volumania! 630 Determining Density 632

Layering Liquids 633 White Before Your Eyes 634

Introduction to MatterTimeline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Unit 1

CHAPTER 1

CHAPTER 2

vi ContentsCopyright © by Holt, Rinehart and Winston. All rights reserved.


Contents vii

States of Matter . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Section 1 Four States of Matter . . . . . . . . . . . . . . . . 60

Section 2 Changes of State . . . . . . . . . . . . . . . . . . . 68


Feature ArticlesScience, Technology, and Society: Guiding Lightning . 78

Eureka!: Full Steam Ahead! . . . . . . . . . . . . . . . . . . . 79

Full of Hot Air! 636 Can Crusher 637 A Hot and Cool Lab 638

Elements, Compounds, and Mixtures . . . . . . . 80

Section 1 Elements . . . . . . . . . . . . . . . . . . . . . . . . . 82

Section 2 Compounds . . . . . . . . . . . . . . . . . . . . . . . 86

Section 3 Mixtures . . . . . . . . . . . . . . . . . . . . . . . . . 90


Feature ArticlesScience, Technology, and Society:

Perfume: Fragrant Solutions . . . . . . . . . . . . . . . . 102

Science Fiction: “The Strange Case of Dr. Jekyll and Mr. Hyde” . . . 103

Flame Tests 640

A Sugar Cube Race! 642

Making Butter 643

Unpolluting Water 644

CHAPTER 3

CHAPTER 4


Contentsviii

Matter in Motion . . . . . . . . . . . . . . . . . . . . . . . . 106

Section 1 Measuring Motion . . . . . . . . . . . . . . . . . 108

Section 2 What Is a Force? . . . . . . . . . . . . . . . . . . 115

Section 3 Friction: A Force That Opposes Motion . . 119

Section 4 Gravity: A Force of Attraction . . . . . . . . 125



Is It Real . . . or Is It Virtual? . . . . . . . . . . . . . . . 134

Across the Sciences: The Golden Gate Bridge . . . . . 135

Built for Speed 646 Detecting Acceleration 647

Science Friction 650 Relating Mass and Weight 651

Forces in Motion . . . . . . . . . . . . . . . . . . . . . . . . 136

Section 1 Gravity and Motion . . . . . . . . . . . . . . . . 138

Section 2 Newton’s Laws of Motion . . . . . . . . . . . 145


Feature ArticlesEureka!: A Bat with Dimples . . . . . . . . . . . . . . . . . 158

Careers: Roller Coaster Designer . . . . . . . . . . . . . . 159

A Marshmallow Catapult 652 Blast Off! 653

Inertia-Rama! 654 Quite a Reaction 656

CHAPTER 5

Motion and ForcesTimeline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

Unit 2

CHAPTER 6


Contents ix

Forces in Fluids . . . . . . . . . . . . . . . . . . . . . . . . . 160

Section 1 Fluids and Pressure . . . . . . . . . . . . . . . . 162

Section 2 Buoyant Force . . . . . . . . . . . . . . . . . . . . 168

Section 3 Bernoulli’s Principle . . . . . . . . . . . . . . . 173


Feature ArticlesEureka!: Stayin’ Aloft—The Story of the Frisbee® . . 182

Science Fiction: “Wet Behind the Ears” . . . . . . . . . . 183

Fluids, Force, and Floating 658 Density Diver 660 Taking Flight 661

Work and Machines . . . . . . . . . . . . . . . . . . . . . 186

Section 1 Work and Power . . . . . . . . . . . . . . . . . . 188

Section 2 What Is a Machine? . . . . . . . . . . . . . . . 192

Section 3 Types of Machines . . . . . . . . . . . . . . . . . 198


Feature ArticlesScience, Technology, and Society: Micromachines . . . 210

Eureka!: Wheelchair Innovators . . . . . . . . . . . . . . . 211

A Powerful Workout 662 Inclined to Move 664

Building Machines 665 Wheeling and Dealing 666

CHAPTER 7

Work, Machines, and EnergyTimeline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184

Unit 3

CHAPTER 8

Copyright © by Holt, Rinehart and Winston. All rights reserved.x

Energy and Energy Resources . . . . . . . . . . . . . 212

Section 1 What Is Energy? . . . . . . . . . . . . . . . . . . 214

Section 2 Energy Conversions . . . . . . . . . . . . . . . . 222

Section 3 Conservation of Energy . . . . . . . . . . . . . 229

Section 4 Energy Resources . . . . . . . . . . . . . . . . . . 232


Feature ArticlesAcross the Sciences: Green Buildings . . . . . . . . . . . 242

Careers: Power-Plant Manager . . . . . . . . . . . . . . . 243

Finding Energy 668 Energy of a Pendulum 670

Eggstremely Fragile 671

Heat and Heat Technology . . . . . . . . . . . . . . . 244

Section 1 Temperature . . . . . . . . . . . . . . . . . . . . . 246

Section 2 What Is Heat? . . . . . . . . . . . . . . . . . . . . 251

Section 3 Matter and Heat . . . . . . . . . . . . . . . . . . . 260

Section 4 Heat Technology . . . . . . . . . . . . . . . . . . 263



The Deep Freeze . . . . . . . . . . . . . . . . . . . . . . . . 274

Across the Sciences:

DiAPLEX®: The Intelligent Fabric . . . . . . . . . . . . 275

Feel the Heat 672

Save the Cube! 674

Counting Calories 675

CHAPTER 9

CHAPTER 10

Contents

Contents xi

Introduction to Atoms . . . . . . . . . . . . . . . . . . . . 278

Section 1 Development of the Atomic Theory . . . . 280

Section 2 The Atom . . . . . . . . . . . . . . . . . . . . . . . 287


Feature ArticlesAcross the Sciences: Water on the Moon? . . . . . . . 298

Careers: Experimental Physicist . . . . . . . . . . . . . . 299

Made to Order 676

The Periodic Table . . . . . . . . . . . . . . . . . . . . . . . 300

Section 1 Arranging the Elements . . . . . . . . . . . . . 302

Section 2 Grouping the Elements . . . . . . . . . . . . . . 310



The Science of Fireworks . . . . . . . . . . . . . . . . . . 322

Weird Science: Buckyballs . . . . . . . . . . . . . . . . . . . 323

Create a Periodic Table 678

CHAPTER 11


The AtomTimeline . . . . . . . . . . . . . . . . 276

Unit 4

CHAPTER 12


Chemical Bonding . . . . . . . . . . . . . . . . . . . . . . . 326

Section 1 Electrons and Chemical Bonding . . . . . . 328

Section 2 Types of Chemical Bonds . . . . . . . . . . . . 332


Feature ArticlesAcross the Sciences: Left-Handed Molecules . . . . . . 346

Eureka!: Here’s Looking at Ya’! . . . . . . . . . . . . . . . 347

Covalent Marshmallows 680

Chemical Reactions . . . . . . . . . . . . . . . . . . . . . . 348

Section 1 Forming New Substances . . . . . . . . . . . . 350

Section 2 Types of Chemical Reactions . . . . . . . . . 358

Section 3 Energy and Rates of Chemical Reactions . 361


Feature ArticlesEye on the Environment: Slime That Fire! . . . . . . . . 370

Careers: Arson Investigator . . . . . . . . . . . . . . . . . . 371

Finding a Balance 682

Cata-what? Catalyst! 683

Putting Elements Together 684

Speed Control 686

CHAPTER 13

Interactions of MatterTimeline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324

Unit 5

CHAPTER 14

Contentsxii

Contents xiii

Chemical Compounds . . . . . . . . . . . . . . . . . . . . 372

Section 1 Ionic and Covalent Compounds . . . . . . . 374

Section 2 Acids, Bases, and Salts . . . . . . . . . . . . . . 377

Section 3 Organic Compounds . . . . . . . . . . . . . . . 383


Feature ArticlesAcross the Sciences: Unique Compounds . . . . . . . . 394

Weird Science: The Secrets of Spider Silk . . . . . . . . 395

Cabbage Patch Indicators 688 Making Salt 690

Atomic Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . 396

Section 1 Radioactivity . . . . . . . . . . . . . . . . . . . . . 398

Section 2 Energy from the Nucleus . . . . . . . . . . . . 406


Feature ArticlesScientific Debate: Wasting Yucca Mountain? . . . . . . 416

Careers: Materials Scientist . . . . . . . . . . . . . . . . . . 417

Domino Chain Reactions 692

CHAPTER 15


CHAPTER 16


Introduction to Electricity . . . . . . . . . . . . . . . . 420

Section 1 Electric Charge and Static Electricity . . . 422

Section 2 Electrical Energy . . . . . . . . . . . . . . . . . . 430

Section 3 Electric Current . . . . . . . . . . . . . . . . . . . 433

Section 4 Electric Circuits . . . . . . . . . . . . . . . . . . . 440



Riding the Electric Rails . . . . . . . . . . . . . . . . . . . 450

Across the Sciences: Sprites and Elves . . . . . . . . . . 451

Stop the Static Electricity! 694 Potato Power 695 Circuitry 101 696

Electromagnetism . . . . . . . . . . . . . . . . . . . . . . . 452

Section 1 Magnets and Magnetism . . . . . . . . . . . . . 454

Section 2 Magnetism from Electricity . . . . . . . . . . 462

Section 3 Electricity from Magnetism . . . . . . . . . . 468


Feature ArticlesAcross the Sciences: Geomagnetic Storms . . . . . . . . 478

Health Watch: Magnets in Medicine . . . . . . . . . . . . 479

Magnetic Mystery 698 Build a DC Motor 700 Electricity from Magnetism 699

CHAPTER 17

ElectricityTimeline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418

Unit 6

CHAPTER 18

Contentsxiv


Contents xv

Electronic Technology . . . . . . . . . . . . . . . . . . . . 480

Section 1 Electronic Components . . . . . . . . . . . . . 482

Section 2 Communication Technology . . . . . . . . . . 488

Section 3 Computers . . . . . . . . . . . . . . . . . . . . . . . 494


Feature ArticlesHealth Watch: Listening Lower . . . . . . . . . . . . . . . . 504

Science Fiction: “There Will Come Soft Rains” . . . . 505

Tune In! 702

The Energy of Waves . . . . . . . . . . . . . . . . . . . . . 508

Section 1 The Nature of Waves . . . . . . . . . . . . . . . 510

Section 2 Properties of Waves . . . . . . . . . . . . . . . . 516

Section 3 Wave Interactions . . . . . . . . . . . . . . . . . 520



The Ultimate Telescope . . . . . . . . . . . . . . . . . . . 530

Across the Sciences: Sounds of Silence . . . . . . . . . . 531

Wave Energy and Speed 706

Wave Speed, Frequency, and Wavelength 708

CHAPTER 19

CHAPTER 20

Waves, Sound, and LightTimeline . . . . . . . . . . . . . . . . 506

Unit 7

Contentsxvi

The Nature of Sound . . . . . . . . . . . . . . . . . . . . . 532

Section 1 What Is Sound? . . . . . . . . . . . . . . . . . . 534

Section 2 Properties of Sound . . . . . . . . . . . . . . . 539

Section 3 Interactions of Sound Waves . . . . . . . . . 545

Section 4 Sound Quality . . . . . . . . . . . . . . . . . . . 552

Chapter Highlights/Review . . . . . . . . . . . . . . . . . . . . 556

Feature ArticlesScience, Technology, and Society: Jurassic Bark . . . . 560

Science Fiction: “Ear” . . . . . . . . . . . . . . . . . . . . . . . 561

Easy Listening 710 The Speed of Sound 712

Tuneful Tube 713 The Energy of Sound 714

The Nature of Light . . . . . . . . . . . . . . . . . . . . . . 562

Section 1 What Is Light? . . . . . . . . . . . . . . . . . . . 564

Section 2 The Electromagnetic Spectrum . . . . . . . 567

Section 3 Interactions of Light Waves . . . . . . . . . 575

Section 4 Light and Color . . . . . . . . . . . . . . . . . . 581



Fireflies Light the Way . . . . . . . . . . . . . . . . . . . . 590

Eureka!: It’s a Heat Wave! . . . . . . . . . . . . . . . . . . . 591

What Color of Light Is Best for Green Plants? 716

Which Color Is Hottest? 717 Mixing Colors 718

CHAPTER 21


CHAPTER 22

Contents xvii

Light and Our World . . . . . . . . . . . . . . . . . . . . . 592

Section 1 Light Sources . . . . . . . . . . . . . . . . . . . . . 594

Section 2 Mirrors and Lenses . . . . . . . . . . . . . . . . . 598

Section 3 Light and Sight . . . . . . . . . . . . . . . . . . . 605

Section 4 Light Technology . . . . . . . . . . . . . . . . . . 608


Feature ArticlesScience, Technology, and Society: Traffic Lights . . . . 618

Eye on the Environment: Light Pollution . . . . . . . . . 619

Mirror Images 720 Images from Convex Lenses 722

CHAPTER 23


. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 620

Self-Check Answers . . . . . . . . . . . . . . 724

Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . 727

Concept Mapping . . . . . . . . . . . . . . . . . . . . . . . . . . 728SI Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . 729Temperature Scales . . . . . . . . . . . . . . . . . . . . . . . . 730Measuring Skills . . . . . . . . . . . . . . . . . . . . . . . . . . . 731Scientific Method . . . . . . . . . . . . . . . . . . . . . . . . . . 732Making Charts and Graphs . . . . . . . . . . . . . . . . . . . 735Math Refresher . . . . . . . . . . . . . . . . . . . . . . . . . . . 738Physical Science Refresher . . . . . . . . . . . . . . . . . . . 742Periodic Table of the Elements . . . . . . . . . . . . . . . . 744Physical Science Laws and Principles . . . . . . . . . . . . 746

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . 750

Spanish Glossary . . . . . . . . . . . . . . . . . 761

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 776


Contentsxviii

The more labs, the better!

Take a minute to browse the LabBook located at the

end of this textbook. You’ll find a wide variety of

exciting labs that will help you experience science

firsthand. But please don’t forget to be safe. Read the

“Safety First!” section before starting any of the labs.

Safety First! . . . . . . . . . . . . . 622CHAPTER 1 The World of Physical Science

Exploring the Unseen . . . . . . . . . . . . . . . 626Off to the Races! . . . . . . . . . . . . . . . . . . . 627Measuring Liquid Volume . . . . . . . . . . . . 628Coin Operated . . . . . . . . . . . . . . . . . . . . 629

CHAPTER 2 The Properties of MatterVolumania! . . . . . . . . . . . . . . . . . . . . . . . 630Determining Density . . . . . . . . . . . . . . . . 632Layering Liquids . . . . . . . . . . . . . . . . . . . 633White Before Your Eyes . . . . . . . . . . . . . . 634

CHAPTER 3 States of MatterFull of Hot Air! . . . . . . . . . . . . . . . . . . . . 636Can Crusher . . . . . . . . . . . . . . . . . . . . . . 637A Hot and Cool Lab . . . . . . . . . . . . . . . . 638

CHAPTER 4 Elements, Compounds, and MixturesFlame Tests . . . . . . . . . . . . . . . . . . . . . . . 640A Sugar Cube Race! . . . . . . . . . . . . . . . . . 642Making Butter . . . . . . . . . . . . . . . . . . . . 643Unpolluting Water . . . . . . . . . . . . . . . . . 644

CHAPTER 5 Matter in MotionBuilt for Speed . . . . . . . . . . . . . . . . . . . . 646Detecting Acceleration . . . . . . . . . . . . . . 647Science Friction . . . . . . . . . . . . . . . . . . . 650Relating Mass and Weight . . . . . . . . . . . . 651

CHAPTER 6 Forces in MotionA Marshmallow Catapult . . . . . . . . . . . . . 652Blast Off! . . . . . . . . . . . . . . . . . . . . . . . . 653Inertia-Rama! . . . . . . . . . . . . . . . . . . . . . 654Quite a Reaction . . . . . . . . . . . . . . . . . . . 656

CHAPTER 7 Forces in FluidsFluids, Force, and Floating . . . . . . . . . . . . 658Density Diver . . . . . . . . . . . . . . . . . . . . . 660Taking Flight . . . . . . . . . . . . . . . . . . . . . 661

CHAPTER 8 Work and MachinesA Powerful Workout . . . . . . . . . . . . . . . . 662Inclined to Move . . . . . . . . . . . . . . . . . . 664Building Machines . . . . . . . . . . . . . . . . . 665Wheeling and Dealing . . . . . . . . . . . . . . 666

CHAPTER 9 Energy and Energy ResourcesFinding Energy . . . . . . . . . . . . . . . . . . . . 668Energy of a Pendulum . . . . . . . . . . . . . . . 670Eggstremely Fragile . . . . . . . . . . . . . . . . . 671

CHAPTER 10 Heat and Heat TechnologyFeel the Heat . . . . . . . . . . . . . . . . . . . . . 672

Save the Cube! . . . . . . . . . . . . . . . . . . . . 674Counting Calories . . . . . . . . . . . . . . . . . . 675

CHAPTER 11 Introduction to AtomsMade to Order . . . . . . . . . . . . . . . . . . . . 676

CHAPTER 12 The Periodic TableCreate a Periodic Table . . . . . . . . . . . . . . 678

CHAPTER 13 Chemical BondingCovalent Marshmallows . . . . . . . . . . . . . 680

CHAPTER 14 Chemical ReactionsFinding a Balance . . . . . . . . . . . . . . . . . . 682Cata-what? Catalyst! . . . . . . . . . . . . . . . . 683Putting Elements Together . . . . . . . . . . . . 684Speed Control . . . . . . . . . . . . . . . . . . . . . 686

CHAPTER 15 Chemical CompoundsCabbage Patch Indicators . . . . . . . . . . . . 688Making Salt . . . . . . . . . . . . . . . . . . . . . . 690

CHAPTER 16 Atomic EnergyDomino Chain Reactions . . . . . . . . . . . . 692

CHAPTER 17 Introduction to ElectricityStop the Static Electricity! . . . . . . . . . . . . 694Potato Power . . . . . . . . . . . . . . . . . . . . . 695Circuitry 101 . . . . . . . . . . . . . . . . . . . . . 696

CHAPTER 18 ElectromagnetismMagnetic Mystery . . . . . . . . . . . . . . . . . . 698Electricity from Magnetism . . . . . . . . . . . 699Build a DC Motor . . . . . . . . . . . . . . . . . . 700

CHAPTER 19 Electronic TechnologyTune In! . . . . . . . . . . . . . . . . . . . . . . . . . 702

CHAPTER 20 The Energy of WavesWave Energy and Speed . . . . . . . . . . . . . 706Wave Speed, Frequency, and Wavelength .708

CHAPTER 21 The Nature of SoundEasy Listening . . . . . . . . . . . . . . . . . . . . 710The Speed of Sound . . . . . . . . . . . . . . . . .712Tuneful Tube . . . . . . . . . . . . . . . . . . . . . 713The Energy of Sound . . . . . . . . . . . . . . . . 714

CHAPTER 22 The Nature of LightWhat Color of Light Is Best for Green Plants? . 716Which Color Is Hottest? . . . . . . . . . . . . . 717Mixing Colors . . . . . . . . . . . . . . . . . . . . 718

CHAPTER 23 Light and Our WorldMirror Images . . . . . . . . . . . . . . . . . . . 720Images from Convex Lenses . . . . . . . . . . 722

Contents xixCopyright © by Holt, Rinehart and Winston. All rights reserved.

Averages . . . . . . . . . . . . 16Using Area to Find

Volume . . . . . . . . . . . 26Calculating Volume . . . . 38Density . . . . . . . . . . . . . 45Gas Law Graphs . . . . . . . 66Calculating

Concentration . . . . . . 94Calculating Average

Speed . . . . . . . . . . . . 109Calculating Acceleration 113Velocity of Falling

Objects . . . . . . . . . . 139Second-Law Problems . . 149Pressure, Force, and Area 162How to Calculate

Density . . . . . . . . . . 170Working It Out . . . . . . 190Finding the Advantage . 196

MATH BREAK

Calculating Energy . . . . 217Converting

Temperatures . . . . . . 249Calculating Energy

Transfer . . . . . . . . . . 257Atomic Mass . . . . . . . . 292Charge! . . . . . . . . . . . . 334Counting Atoms . . . . . 352Balancing Act . . . . . . . . 356How Old Is It? . . . . . . . 404Using Ohm’s Law . . . . . 437Computer Memory . . . . 497Perpendicular Lines . . . 513Wave Calculations . . . . 519Speed of Sound . . . . . . 540Just How Fast Is Light? . . 566

Start your engines

with an activity!

Science is an activity in which

investigation leads to information

and understanding. The Start-Up

Activity at the beginning of each

chapter helps you gain scientific

understading of the topic through

hands-on experience.

Which Is Quicker? . . . . 364I’m Crushed! . . . . . . . . 365pHast Relief! . . . . . . . . 380Gone Fission . . . . . . . . 407A Series of Circuits . . . 442A Parallel Lab . . . . . . . 443Electromagnets . . . . . . 464Springy Waves . . . . . . . 518Good Vibrations . . . . . 534Sounding Board . . . . . . 543Scattering Milk . . . . . . 577Rose-Colored Glasses? . . 584Now You See,

Now You Don’t . . . . 613

Not all laboratoryinvestigations haveto be long andinvolved.The QuickLabs found through-out the chapters in this bookrequire only a small amount oftime and limited equipment.But just because they are quick,don’t skimp on the safety.

Figure it Out . . . . . . . . . . . 5Sack Secrets . . . . . . . . . . . 35Vanishing Act . . . . . . . . . . 59Mystery Mixture . . . . . . . . 81The Domino Derby . . . . . 107Falling Water . . . . . . . . . 137Taking Flight . . . . . . . . . 161C’mon, Lever a Little! . . . 187Energy Swings! . . . . . . . . 213Some Like It Hot . . . . . . . 245Where Is It? . . . . . . . . . . 279Placement Pattern . . . . . . 301From Glue to Goop . . . . . 327A Model Formula . . . . . . 349Sticking Together . . . . . . 373Watch Your Headsium! . . 397Charge over Matter . . . . . 421Magnetic Attraction . . . . 453Talking Long Distance . . . 481Energetic Waves . . . . . . . 509A Homemade Guitar . . . . 533Colors of Light . . . . . . . . 563Mirror, Mirror . . . . . . . . . 593

That’s Swingin’! . . . . . . 15Space Case . . . . . . . . . . 36Changing Change . . . . . 49Boiling Water Is Cool . . 71Compound Confusion . . 87The Friction 500 . . . . . 120Penny Projectile

Motion . . . . . . . . . . 144First-Law Magic . . . . . . 147Blown Away . . . . . . . . 166Ship-Shape . . . . . . . . . 171Breathing Bernoulli-

Style . . . . . . . . . . . . 173More Power to You . . . 191Hear That Energy! . . . . 220Hot or Cold? . . . . . . . . 247Heat Exchange . . . . . . 253Conduction

Connection . . . . . . . 307Bending with Bonds . . 340Mass Conservation . . . 357

Science and math

go hand in hand.

The MathBreaks in the

margins of the chapters

show you many ways that

math applies directly to

science and vice versa.


Contentsxx

Science can be very useful in the real world.It is interesting to learn how scientific information is being used in the real world. You can see for yourself in the Apply features.You will also be asked to apply your own knowledge. This is agood way to learn!Models for Weather

Forecasting . . . . . . . . . . 21Mass, Weight, and

Bathroom Scales . . . . . . 42Density and Grease

Separators . . . . . . . . . . . 46Charles’s Law and

Bicycle Tires . . . . . . . . . 67Shake Well Before Use . . . . 96Friction and Tires . . . . . . 124Stopping Motion . . . . . . . 146Lift and Spoilers . . . . . . . 176

Oil Improves Efficiency . . 197Camping with Energy . . . 224Keepin’ It Cool . . . . . . . . 254Isotopes and Light Bulbs . . 291One Set of Symbols . . . . . 308Metallic Bonding

in Staples . . . . . . . . . . 341Fresh Hydrogen Peroxide . 363Storage Site Selection . . . 409

How to Save Energy . . . . 439Compasses Near

Magnets . . . . . . . . . . . 463Sound Waves in Movie

Theaters . . . . . . . . . . . 523Insightful Technology . . . 547Blocking the Sun . . . . . . . 573Convex Mirrors

Help Drivers . . . . . . . . 602

BiologyC O N N E C T I O NAll About Penguins . . . . . . 14 Calcium Strengthens Bones . . 40Blood: Part Suspension,

Part Solution . . . . . . . . . 96Seeds Can “Sense” Gravity . . 125Energy Conversions

in the Body . . . . . . . . . 231Energy in Food . . . . . . . . 262Covalent Bonds

in Proteins . . . . . . . . . 339Photosynthesis, Cellular

Respiration, and Energy . . 362pH of Blood . . . . . . . . . . 381Essential Amino Acids . . . 386“Jump Start” a Heart . . . . 435Your Body’s Wired . . . . . . 441Do Birds Use Magnets to

Navigate? . . . . . . . . . . 460Vocal Cords and Speech . . 535Waves of Therapy . . . . . . 541Photosynthesis . . . . . . . . 572Color Deficiency and

Chromosomes . . . . . . . 607

Breaking Down CompoundsUsing Electrolysis . . . . . 88

Density Differences Affect the Earth’s Crust . . . . . 172

From Alpha to Helium . . 399Seismograms Are

Analog Signals . . . . . . .489Using Minerals in Paint . . 585

EnvironmentC O N N E C T I O N

GeologyC O N N E C T I O N

AstronomyC O N N E C T I O N

PhysicsC O N N E C T I O N

Condensation and FogFormation . . . . . . . . . . . 71

Coastal Climates . . . . . . . 256

MeteorologyC O N N E C T I O N

Energy from the Ocean . . 266

OceanographyC O N N E C T I O N

Chemical Changes and AcidPrecipitation . . . . . . . . . 51

Newton’s Second Law and Air Pollution . . . . 148

Heat Island Effect . . . . . . 269Recycling Aluminum . . . . 314Radon in the Home . . . . 402Noise Pollution

and Butterflies . . . . . . 555

The Gravitational Force of Black Holes . . . . . . . 127

Hydrogen: The Most Abundant Element . . . 290

Star Fuel . . . . . . . . . . . . . 410Light from the Stars . . . . 512Communication Break . . . 536Speed of Electromagnetic

Waves . . . . . . . . . . . . 567What Makes the

Moon Shine? . . . . . . . 594

One science leads to another.You may not realize it at first, but different areas of science are related

to each other in many ways. Each Connection explores a topic from

the viewpoint of another science discipline. In this way, areas of

science merge to improve your understanding of the world around you.

Connections

Copyright © by Holt, Rinehart and Winston. All rights reserved.xxiContents

Buckyballs . . . . . . . . . . . . . . . . . . . . 323The Secrets of Spider Silk . . . . . . . . . . 395

In the Dark About Dark Matter . . . . . . . 56The Golden Gate Bridge . . . . . . . . . . . 135Green Buildings . . . . . . . . . . . . . . . . . 242DiAPLEX®: The Intelligent Fabric . . . . . 275Water on the Moon? . . . . . . . . . . . . . 298Left-Handed Molecules . . . . . . . . . . . . 346Unique Compounds . . . . . . . . . . . . . 394Sprites and Elves . . . . . . . . . . . . . . . . 451Geomagnetic Storms . . . . . . . . . . . . . 478Sounds of Silence . . . . . . . . . . . . . . . . 531

Feature Articles

Electronics Engineer . . . . . . . . . . . . . . 32Roller Coaster Designer . . . . . . . . . . . 159Power-Plant Manager . . . . . . . . . . . . 243Experimental Physicist . . . . . . . . . . . . 299Arson Investigator . . . . . . . . . . . . . . . 371Materials Scientist . . . . . . . . . . . . . . . 417

Guiding Lightning . . . . . . . . . . . . . . . 78Perfume: Fragrant Solutions . . . . . . . . 102Is It Real . . . or Is It Virtual? . . . . . . . 134Micromachines . . . . . . . . . . . . . . . . . 210The Deep Freeze . . . . . . . . . . . . . . . . . 274The Science of Fireworks . . . . . . . . . . 322Riding the Electric Rails . . . . . . . . . . . 450The Ultimate Telescope . . . . . . . . . . . . 530Jurassic Bark . . . . . . . . . . . . . . . . . . . 560Fireflies Light the Way . . . . . . . . . . . . 590Traffic Lights . . . . . . . . . . . . . . . . . . . 618

Slime That Fire! . . . . . . . . . . . . . . . . . 370Light Pollution . . . . . . . . . . . . . . . . . 619

Full Steam Ahead! . . . . . . . . . . . . . . . . 79A Bat with Dimples . . . . . . . . . . . . . . 158Stayin’ Aloft—The Story of the Frisbee® . 182Wheelchair Innovators . . . . . . . . . . . . 211Here’s Looking at Ya’! . . . . . . . . . . . . . 347It’s a Heat Wave! . . . . . . . . . . . . . . . . 591

Building a Better Body . . . . . . . . . . . . . 57Magnets in Medicine . . . . . . . . . . . . . 479Listening Lower . . . . . . . . . . . . . . . . . 504

Wasting Yucca Mountain? . . . . . . . . . . 416

“Inspiration”. . . . . . . . . . . . . . . . . . . . 33“The Strange Case of Dr. Jekyll and

Mr. Hyde” . . . . . . . . . . . . . . . . . . . 103“Wet Behind the Ears” . . . . . . . . . . . . 183“There Will Come Soft Rains” . . . . . . . 505“Ear” . . . . . . . . . . . . . . . . . . . . . . . . 561

Feature articles for any appetite! Science and technology affect us all in manyways. The following articles will give you anidea of just how interesting, strange, helpful,and action-packed science and technology are.At the end of each chapter, you will find twofeature articles. Read them and you will besurprised at what you learn.

SCIENTIFICDEBATE

CAR E E R S


How to Use Your Textbookxxii

Chapter 360

Four States of MatterFigure 1 shows a model of theearliest known steam engine,invented about A.D. 60 byHero, a scientist who lived inAlexandria, Egypt. This modelalso demonstrates the fourmost familiar states of matter:solid, liquid, gas, and plasma.The states of matter are thephysical forms in which a sub-stance can exist. For example,water commonly exists inthree different states of mat-ter: solid (ice), liquid (water),and gas (steam).

Moving Particles Make Up All MatterMatter consists of tiny particles called atoms and molecules(MAHL i KYOOLZ) that are too small to see without an amazinglypowerful microscope. These atoms and molecules are always inmotion and are constantly bumping into one another. The stateof matter of a substance is determined by how fast the particlesmove and how strongly the particles are attracted to one another.Figure 2 illustrates three of the states of matter—solid, liquid,and gas—in terms of the speed and attraction of the particles.

Figure 1 This model of Hero’ssteam engine spins as steamescapes through the nozzles.

Particles of a solid do not movefast enough to overcome thestrong attraction between them,so they are held tightly in place.The particles vibrate in place.

Particles of a liquid move fastenough to overcome some ofthe attraction between them.The particles are able to slidepast one another.

Particles of a gas move fastenough to overcome nearlyall of the attraction betweenthem. The particles moveindependently of one another.

Figure 2 Models of a Solid, a Liquid, and a Gas

Gas

Solid

Liquid

Plasma

Section

1

states of matter pressuresolid Boyle’s lawliquid Charles’s lawgas plasma

Describe the properties sharedby particles of all matter.

Describe the four states of mat-ter discussed here.

Describe the differencesbetween the states of matter.

Predict how a change in pres-sure or temperature will affectthe volume of a gas.

Your Roadmap for Success with Holt Science & Technology

Internet Connect boxes inyour textbook take you toresources that you can use forscience projects, reports, and

research papers. Go to scilinks.org and type inthe SciLinks code to get information on a topic.

Visit go.hrw.comFind worksheets andother materials that

go with your textbook at go.hrw.com.Click on the textbook icon and thetable of contents to see all of theresources for each chapter.

Study the Terms to LearnKey Terms are listed for each section. Learn the definitions of these terms because you will most likely be tested on them. Use the glossary to locate definitions quickly.

STUDY TIP If you don’t understand adefinition, reread the page where the term isintroduced. The surrounding text should helpmake the definition easier to understand.

Read What You’ll Do Objectives tell you what you’ll need to know.

STUDY TIP Reread the objectives whenstudying for a test to be sure you know the material.

Take Notes and Get OrganizedKeep a science notebook so that you are ready to take notes when your teacher reviews the material in class. Keep yourassignments in this notebook so that you can review them when studying for thechapter test. In addition, you will be asked to keep a ScienceLog, in which you will write your answers to certain questions. Your ScienceLog may be a section of your science notebook.

Be Resourceful, Use the Web

How to Use Your Textbook

How to Use Your Textbook xxiiiCopyright © by Holt, Rinehart and Winston. All rights reserved.

Other Ways of Producing Electrical EnergyThe conversion of chemical energy to electrical energy in bat-teries is not the only way electrical energy can be generated.Several technological devices have been developed to convertdifferent types of energy into electrical energy for use everyday. For example, generators convert kinetic energy into elec-trical energy. Two other devices that produce electrical energyare photocells and thermocouples.

Photocells Have you ever wondered how a solar-powered cal-culator works? If you look above the display of the calculator,you will see a dark strip called a solar panel. This panel ismade of several photocells. A photocell is the part of a solarpanel that converts light into electrical energy.

Photocells contain silicon atoms.When light strikes the photocell,electrons are ejected from the siliconatoms. If light continues to shine onthe photocell, electrons will besteadily emitted. The ejected elec-trons are gathered into a wire to create an electric current.

Thermocouples Thermal energy canbe converted to electrical energy by athermocouple. A simple thermocoupleis made by joining wires made of twodifferent metals into a loop, as shownin Figure 14. The temperature differ-ence within the loop causes charges toflow through the loop. Thermocouplesare used to monitor the temperatureof car engines, furnaces, and ovens.

Chapter 17432

1. Name the parts of a cell, and explain how they worktogether to produce an electric current.

2. How do the currents produced by a 1.5 V flashlight celland a 12 V car battery compare?

3. Inferring Conclusions Why do you think some solarcalculators contain batteries?

Figure 14 A Simple Thermocouple

REVIEW

Copper wire

Burner Iron wire

Ice water

Meter

The greater the temperature differ-ence is, the greater the current.

Solar panel

One section of the loop is heated.

One section of theloop is cooled.

NSTA

TOPIC: Electrical EnergyGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP410

Second Class Levers With asecond class lever, the load isbetween the fulcrum and theinput force, as shown in Figure 11.Second class levers do not changethe direction of the input force,but they allow you to apply lessforce than the force exerted bythe load. Because the output forceis greater than the input force,you must exert the input forceover a greater distance. Someexamples of second class leversare shown at right.

Third Class Levers With athird class lever, the input forceis between the fulcrum and theload, as shown in Figure 12. Thirdclass levers do not change thedirection of the input force. Inaddition, they do not increase the input force. Therefore, theoutput force is always less than the input force. Some examplesof third class levers are shown at right.

Work and Machines 199

Input force

Output force

Fulcrum

Examples of Second Class Levers

Using a second class leverresults in a mechanicaladvantage of greater than 1.The closer the load is to thefulcrum, the more the forceis increased and the greaterthe mechanical advantage.

Examples of Third Class Levers

Using a third class lever results in a mechanical advantageof less than 1 because force is decreased. But third classlevers are helpful because they increase the distancethrough which the output force is exerted.

Figure 11 A Second Class Lever

Output force

Input force

Fulcrum

Figure 12 A Third Class Lever

Load

Load

Use the Illustrations and PhotosArt shows complex ideas and processes. Learn to analyze the art so that you better understandthe material you read in the text.

Tables and graphs display importantinformation in an organized way to help you see relationships.

A picture is worth a thousand words. Look at the photographs to see relevant examples ofscience concepts you are reading about.

Answer the Section ReviewsSection Reviews test your knowledge over themain points of the section. Critical Thinkingitems challenge you to think about the material in greater depth and to find connections that you infer from the text.

STUDY TIP When you can’t answer a question,reread the section. The answer is usually there.

Do Your HomeworkYour teacher may assign worksheets to help youunderstand and remember the material in thechapter.

STUDY TIP Don’t try to answer the questionswithout reading the text and reviewing yourclass notes. A little preparation up front willmake your homework assignments a lot easier.Answering the items in the Chapter Review will help prepare you for the chapter test.

Visit Holt Online LearningIf your teacher gives you a specialpassword to log onto the Holt OnlineLearning site, you’ll find your complete

textbook on the Web. In addition, you’ll find some greatlearning tools and practice quizzes. You’ll be able to seehow well you know the material from your textbook.

Visit CNN Student NewsYou’ll find up-to-date events in science atcnnstudentnews.com.

T I M E L I N E

U N I T Introduction to Matter

2

1n this unit, you willexplore a basic

question that peoplehave been ponderingfor centuries: What isthe nature of matter?You will learn how todefine the word matter and how todescribe matter andthe changes it goesthrough. You will alsolearn about the differ-ent states of matterand how to classifydifferent arrangementsof matter as elements,compounds, or mix-tures. This timelineshows some of theevents and discoveriesthat have occurredthroughout history asscientists have soughtto understand thenature of matter.

I1661

Robert Boyle, a chemist inEngland, determines that

elements are substances thatcannot be broken down into anything simpler by

chemical processes.

1957The space age begins

when the Soviet Unionlaunches Sputnik I, thefirst artificial satellite to

circle the Earth.

1971The first “pocket” calculator is

introduced. It has a mass of morethan 1 kg and a price of about$150—hardly the kind of pocket

calculator that exists today.

1949Silly Putty® is sold in a toy store forthe first time. The soft, gooey sub-stance quickly becomes popularbecause of its strange properties,

including the ability to “pick up” theprint from a newspaper page.

1712Thomas Newcomen

invents the first practical steam engine.

Unit 1Copyright © by Holt, Rinehart and Winston. All rights reserved.

1800Current from an electric batteryis used to separate water intothe elements hydrogen and

oxygen for the first time.

1920American women win the

right to vote with the ratificationof the 19th Amendment

to the Constitution.

1928Sir Alexander Fleming discovers

that the mold Penicilliumnotatum, shown here

growing on an orange, iscapable of killing sometypes of bacteria. Theantibiotic penicillin is

derived from this mold.

1989An oil tanker strikes a reef inPrince William Sound, Alaska,

spilling nearly 11 million gallonsof oil. The floating oil injures or

kills thousands of marinemammals and seabirds and

damages the Alaskan coastline.

2000The World’s Fair, an international exhibi-tion featuring exhibits and participants

from around the world, is held inHanover, Germany. The theme is

“Humankind, Nature, and Technology.”

3Introduction to Matter

1937The Hindenburg explodes while

docking in Lakehurst, NewJersey. The airship was filled

with flammable hydrogen gasto make it lighter than air.

1766English chemist Henry

Cavendish discovers anddescribes the properties of ahighly flammable substance

now known as hydrogen gas.


4 Chapter 1

Exploring PhysicalScience. . . . . . . . . . . . . . 6

Internet Connect . . . . . 10

Using the ScientificMethod. . . . . . . . . . . . . 11

Biology Connection . . . 14QuickLab . . . . . . . . . . . 13Internet Connect . . . . . 19

Using Models in Physical Science . . . . . . 20

Internet Connect . . . . . 27

Measurement and Safetyin Physical Science . . . . 24

MathBreak . . . . . . . . . . 26Internet Connect . . . . . 27

Chapter Review . . . . . . . . . . 30

Feature Articles . . . . . . . 32, 33

LabBook . . . . . . . . . . . 626–629

The World ofPhysical ScienceThe World ofPhysical Science

Pre-ReadingQuestions

1. What are scientific methods?

2. What is a model, and what are the limitationsof models?

3. What tools are used tomeasure mass and volume?


5

FIGURE IT OUTIn this activity, you will do somethings scientists do—make observa-tions and use them to solve a puzzle.

Procedure

1. Get the five shapes shown belowfrom your teacher.

2. Observe the drawing below.Predict how the five shapes couldbe arranged to make the fish.

3. Test your idea. You may have to tryseveral times. (Hint: Shapes can beturned over.) Record notes abouteach try in your ScienceLog.

Analysis

4. Did you solve the puzzle just by making observations? Whatobservations helped the most?

5. How did testing your ideas help?

Should a Ship Have Flippers?Putting flippers on a ship may seem like a strangeidea. But think about how well penguins use flippersto move through the water. Maybe flippers couldhelp ships too. This is exactly what two scientistsfrom the Massachusetts Institute of Technology have been trying to find out. In this chapter, you will learn how these scientists have used scientific methods to answer their questions. Maybe, as a result of these investigations, ships will have flippers someday!

The World of Physical ScienceCopyright © by Holt, Rinehart and Winston. All rights reserved.

Section

1

physical science

Describe physical science as thestudy of energy and matter.

Explain the role of physical sci-ence in the world around you.

Name some careers that rely onphysical science.

6

Exploring Physical ScienceIt’s Monday morning. You’re eating breakfast and trying topull yourself out of an early morning daze. As you eat aspoonful of Crunch Blasters, your favorite cereal, you lookdown and notice your reflection in your spoon. Something’sfunny about it—it’s upside down! “Why is my reflectionupside down even though I’m holding the spoon right sideup?” you wonder. Is your spoon playing tricks on you? Nextyou look at the back of the spoon. “A-ha!” you think, “Nowmy reflection is right side up!” However, when you look backat the inside of the spoon, your reflection is upside downagain. What is it about the spoon that makes your reflection

look right side up on one side and upside downon the other?

That’s Science!You may not realize it, but youwere just doing science.Science is all about being curi-ous, making observations,and asking questions aboutthose observations. Forexample, you noticed yourreflection in your spoon andbecame curious about it. You

observed that it was upsidedown, but that when you

looked at the back of the spoon,your reflection was right side up.

Then you asked what the two sidesof the spoon had to do with your reflec-

tion. So you were definitely doing science!

Everyday Science Science is all around you, even if you’renot thinking about it. Everyday actions such as putting on yoursunglasses when you’re outside, timing your microwave pop-corn just right, and using the brakes on your bicycle all useyour knowledge of science. But how do you know how to dothese things? From experience—you’ve gained an understand-ing of your world by observing and discovering all your life.

Because science is all around, you might not be surprisedto learn that there are different branches of science. This bookis all about physical science. So just what is physical science?

Chapter 1Copyright © by Holt, Rinehart and Winston. All rights reserved.

Matter + Energy Physical SciencePhysical science is the study of mat-ter and energy. Matter is the “stuff”that everything is made of—evenstuff that is so small you can’t seeit. Your shoes, your pencil, and eventhe air you breathe are made of mat-ter. And all of that matter has energy.Energy is easier to describe than toexplain. For example, energy is partlyresponsible for rainbows in the sky,but it isn’t the rainbow itself. Whenyou throw a ball, you give the ballenergy. Moving objects have energy,as you can see in Figure 1. Food alsohas energy. When you eat food, theenergy in the food is transferred toyou, and you can use that energy tocarry out your daily activities. Butenergy isn’t always associated withmotion or food. All matter hasenergy, even matter that isn’t mov-ing, like that shown in Figure 2.

As you explore physical science,you’ll learn more about the rela-tionship between matter and energyby answering questions such as thefollowing: Why does paper burn butgold does not? Why is it harder tothrow a bowling ball than a base-ball? How can water turn into steamand back to water? All of the answershave to do with matter and energy.And although it is difficult to talkabout matter without talking aboutenergy, sometimes it is useful tofocus on one or the other. That’s why physical science is often dividedinto two categories—chemistry andphysics.

The World of Physical Science 7

Figure 2 All matter has energy—even this monumental stone headthat is over 1.5 m tall!

Figure 1 The cheetah, the fastest land mammal, has a lot ofenergy when running full speed. The cheetah also uses a lotof energy to run so fast. But a successful hunt will supply theenergy the cheetah needs to live.


Chemistry Studying all forms of matter and how they inter-act is what chemistry is all about. You’ll learn about theproperties and structure of matter and how different substances

behave under certain conditions, such as high tempera-ture and high pressure. You’ll also discover how and

why matter can go through changes, such as the oneshown in Figure 3. Check out the chart below tofind out what you can learn by studying chemistry.

Physics Like chemistry, physics deals with mat-ter. But unlike chemistry, physics is mostly con-cerned with energy and how it affects matter.Studying different forms of energy is what physicsis all about. When you study physics, you’ll dis-cover how energy can make matter do some inter-esting things, as shown in Figure 4. You’ll alsobegin to understand aspects of your world suchas motion, force, gravity, electricity, light, andheat. Check out the chart below to find out whatyou can learn by studying physics.

Chapter 18

Figure 4 When you study physics you’lllearn how energy causes the motion thatmakes a roller coaster ride so exciting.

Figure 3 When you wash your clothes, the detergent and the stains interact. The result? Clean clothes!

By studying chemistry, you can find out . . .

why yeast makes bread dough rise.

how the elements chlorine and sodium combineto form table salt, a compound.

why water boils at 100°C.

why sugar dissolves faster in hot tea than in iced tea.

how pollution affects our atmosphere.

By studying physics, you can find out . . .

why you move to the right when the car you’re inturns left.

why you would weigh less on the moon than youdo on Earth.

why you see a rainbow after a rainstorm.

how a compass works.

how your bicycle’s gears help you pedal faster orslower.


Physical Science Is All Around YouBelieve it or not, the things that you’ll learn about matter andenergy by studying physical science are important for whatyou’ll learn in other science classes, too. Take a look belowto see the role of physical science in areas that you mighthave thought only involved Earth science or life science.


Meteorology applies physical sciencein its study of the movement of airmasses, weather patterns, and thecomposition of the atmosphere.

Geology uses physical scienceto explain earthquake wavesand rock composition.

Botany, the study of plants, usesphysical science to explain howplants use carbon dioxide andwater to make food.

Oceanography uses physicalscience to explain waves,currents, and the chemistryof ocean water.

Biology uses physical scienceto explain how the heartpumps blood, how the eyesand ears work, and how thebrain sends electrical impulsesthroughout the body.

Ecology uses physical science toexplain the nitrogen cycle andthe transfer of energy between organisms in a food chain.

Astronomy uses physical science to explain the composition ofplanets, the light given offby stars, and the motion ofdifferent galaxies in the universe.


Physical Science in Action Now that you know physical science is all around you, youmay not be surprised to learn that a lot of careers rely onphysical science. What’s more, you don’t have to be a scien-tist to use physical science in your job! On this page, you cansee some career opportunities that involve physical science.

1. What is physical science all about?

2. List three things you do every day that use your experi-ence with physical science.

3. Applying Concepts Choose one of the careers listed inthe chart at left. How do you think physical science isinvolved in that career?

Chapter 110

REVIEWOther Careers Involving Physical Science

Architect Pharmacist Firefighter Engineer Construction worker Optician Pilot Electrician Computer technician

Gene Webb is an auto mechanic.He understands how the parts ofa car engine move and how tokeep cars working efficiently.

Shirley Ann Jackson has doneresearch in the semiconductorand optical physics industries. Shebecame president of RensselaerPolytechnic Institute in 1999.

Roberto Santibanez is a chef. Heknows how ingredients interactand how energy can cause thechemical changes that producehis delicious meals.

Julie Fields is a chemist whostudies chemical substancesfound in living organisms. She investigates how thesesubstances can be made intoproducts such as medicines.

NSTA

TOPIC: Matter and EnergyGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP005


Using the Scientific MethodWhen you hear or read about advancements in science, doyou wonder how they were made? How did the scientists maketheir discoveries? Were they just lucky? Maybe, but chancesare that it was much more than luck. The scientific methodprobably had a lot to do with it!

What Is the Scientific Method?The scientific method is a series of steps that scientists use toanswer questions and solve problems. The chart below showsthe steps that are commonly used in the scientific method.Although the scientific method has several distinct steps, it isnot a rigid procedure whose steps must be followed in a certainorder. Scientists may use the steps in a different order, skip steps,

or repeat steps. It all dependson what works best to answerthe question.

Do you remember JamesCzarnowski and MichaelTriantafyllou, the two scien-tists discussed at the begin-ning of this chapter? Whatscientific problem were theytrying to solve? In the nextfew pages, you’ll learn howthey used the scientificmethod to develop new technology—Proteus, the pen-guin boat.

11The World of Physical Science

The Scientific Method

Ask a question.

Form a hypothesis.

Test the hypothesis.

Analyze the results.

Draw conclusions.

Communicate results.

Section

2

scientific method datatechnology theoryobservation lawhypothesis

Identify the steps used in thescientific method.

Give examples of technology. Explain how the scientific

method is used to answer ques-tions and solve problems.

Describe how our knowledge ofscience changes over time.

Spotlight on Technology

Technology is the application of knowledge,tools, and materials to solve problems andaccomplish tasks. Technology can also refer tothe objects used to accomplish tasks. Forexample, computers, headphones, and theInternet are all examples of technology.But even things like toothbrushes, lightbulbs, and pencils are examples oftechnology.

Scienceand technology

are not the same thing.The goal of science is to

gain knowledge about thenatural world. The goal of tech-

nology is to apply scientificunderstanding to solve prob-

lems. Technology is some-times called applied

science.



Ask a QuestionAsking a question helps you focus your investigation and iden-tify what you want to find out. Usually, scientists ask a ques-tion after they’ve made a lot of observations. An observationis any use of the senses to gather information. Measurementsare observations that are made with instruments, such as thoseshown in Figure 5. The chart below gives you some examplesof observations. Keep in mind that you can make observationsat any point while using the scientific method.

A Real-World Question So what question did the scientistswho made Proteus ask? Czarnowski and Triantafyllou, shownin Figure 6, are engineers, scientists who put scientific knowl-edge to practical human use. Engineers create technology. Whilea graduate student at the Massachusetts Institute of Technology,Czarnowski worked with Triantafyllou, his professor, to observeboat propulsion systems and investigate how to make themwork better. A propulsion (proh PUHL shuhn) system is whatmakes a boat move; most boats are driven by propellers.

One thing that Czarnowski andTriantafyllou were studying is theefficiency of boat propulsion sys-tems. Efficiency (e FISH uhn see)compares energy output (the energyused to move the boat forward) withenergy input (the energy suppliedby the boat’s engine). Czarnowskiand Triantafyllou learned from theirobservations that boat propellers,shown in Figure 7 on the next page,are not very efficient.

12 Chapter 1

Figure 5Stopwatches and rulers are some of the manytools used to makeobservations.

Examples of Observations

The sky is blue.

The ice began to melt 30 sec-onds after it was taken out ofthe freezer.

This soda bottle has a volumeof 1 liter.

Cotton balls feel soft.

He is 125 centimeters tall.

Adding food coloring turnedthe water red. Adding bleachmade the water clear again.

This brick feels heavier thanthis sponge.

Sandpaper is rough.

Figure 6 James Czarnowski (left) and Michael Triantafyllou(right) made observations about how boats work in order todevelop Proteus.


Why is boat efficiency important? Most boats are only about70 percent efficient. Making only a small fraction of the UnitedStates’ boats and ships just 10 percent more efficient wouldsave millions of liters of fuel per year. Saving fuel means sav-ing money, but it also means using less of the Earth’s supplyof fossil fuels. Based on their observations and all of this infor-mation, Czarnowski and Triantafyllou knew what they wantedto find out.

Propellers require a lot ofenergy to rotate, and someof that energy gets wastedin churning up the water.Only 70 percent of theenergy put into a propellersystem actually works tomove the boat forward.

Efficiency =

Efficiency is usually expressed as a percent-age. If much more energy is put into a sys-tem than the system puts out, then thesystem is not very efficient, and the percentefficiency will be low.

output energyinput energy

The Question:How can boat propulsion systems be made more efficient?


Figure 7 Observations About the Efficiency of Boat Propellers

Propellers are rotated bymotors. As the propellers whirlaround, they push against thewater. As the water pushesback, the boat moves forward.

Ask some questions of yourown on page 626 in the

LabBook.

a

b

c


Form a HypothesisOnce you’ve asked your question, your next step is forming ahypothesis. A hypothesis is a possible explanation or answerto a question. You can use what you already know and anyobservations that you have made to form a hypothesis. A goodhypothesis is testable. If no observations or information canbe gathered or if no experiment can be designed to test thehypothesis, it is untestable.

Nature Provides a Possible AnswerCzarnowski and Triantafyllou were also lookingfor an example from nature on which to basetheir hypothesis. Czarnowski had made obser-vations of penguins swimming at the NewEngland Aquarium. Figure 8 shows how penguins

propel themselves. He observed how quicklyand easily the penguins moved through

the water. He also observed that pen-guins have a rigid body, similar to aboat. These observations led the twoscientists to a possible answer to theirquestion: a propulsion system thatworks the way a penguin swims!

Before scientists test a hypothesis, they often make pre-dictions that state what they think will happen during theactual test of the hypothesis. Scientists usually state predic-tions in an “If . . . then . . .” format. The engineers at MITmight have made the following prediction: If two flippers are attached to a boat, then the boat will be more efficientthan a boat powered by propellers.

1. How do scientists and engineers use the scientific method?

2. Give three examples of technology from your everyday life.

3. Analyzing Methods Explain how the accuracy of yourobservations might affect how you develop a hypothesis.

Chapter 114

REVIEW

Hypothesis:A propulsion system that mimics the way a penguinswims will be more efficient than propulsion systemsthat use propellers.

Figure 8 Penguins use their flippers almost like wings to “fly” under-water. As they pull theirflippers toward theirbody, they push againstthe water, which propelsthem forward.

BiologyC O N N E C T I O N

Penguins, although flightless, are bet-ter adapted to water and extremecold than any other bird. Most of theworld’s 18 penguin species live andbreed on islands in the subantarcticwaters. Penguins can swim as fast as40 km/h, and some can leap morethan 2 m above the water.


Test the HypothesisAfter you form a hypothesis, you must test it to deter-mine whether it is a reasonable answer to your question.In other words, testing helps you find out if your hypoth-esis is pointing you in the right direction or if it is wayoff the mark. Often a scientist will test a hypothesis bytesting a prediction.

One way to test a hypothesis is to conduct a con-trolled experiment. In a controlled experiment, there isa control group and an experimental group. Both groupsare the same except for one factor in the experimentalgroup, called a variable. The experiment will then deter-mine the effect of the variable.

Sometimes a controlled experiment is not possible.Stars, for example, are too far away to be used in anexperiment. In such cases, you can test your hypothesisby making additional observations or by conductingresearch. If your investigation involves creating tech-nology to solve a problem, you can make or build whatyou want to test and see if it does what you expected itto do. That’s just what Czarnowski and Triantafyllou did—they built Proteus, the penguin boat, shown in Figure 9.

Figure 9 Testing Penguin Propulsion


That’s Swingin’!

1. Make a pendulumby tying a piece ofstring to a ringstand and hanging a smallmass, such as a washer,from the end of the string.

2. Form a hypothesis aboutwhich factors (such aslength of string, mass, etc.)affect the rate at which thependulum swings.

3. In your ScienceLog, recordwhat factors you will con-trol and what factor will beyour variable.

4. Test your hypothesis byconducting several trials,recording the number ofswings made in a giventime, such as 10 seconds,for each trial.

5. Was your hypothesis sup-ported? In your ScienceLog,analyze your results.Proteus is only 3.4 m long and 50 cm wide,

too narrow for even a single passenger.

A desktop computerprograms the numberof times the foils flapper second.

Each of Proteus’s flappingfoils is driven by a motorthat gets its energy fromtwo car batteries.

As the foils flap, they push waterbackward. The water pushes againstthe foils, propelling the boat forward.

e

a

c

d

Proteus has two flipper-like paddles, called foils. Both foils moveout and then in, much as a penguin uses its flippers underwater.

b


Testing Proteus Czarnowski and Triantafyllou took Proteusout into the open water of the Charles River when they wereready to collect data. Data are any pieces of information acquiredthrough experimentation. The engineers did several tests, eachtime changing only the flapping rate. For each test, data suchas the flapping rate, energy the motors used, and the speedachieved by the boat were carefully recorded. The input energywas determined by how much energy was used. The outputenergy was determined from the speed Proteus achieved.

Analyze the ResultsAfter you collect and record your data, you must analyzethem to determine whether the results of your test supportthe hypothesis. Sometimes doing calculations can help youlearn more about your results. Organizing numerical datainto tables and graphs makes relationships between infor-mation easier to see.

Analyzing Proteus Czarnowski and Triantafyllou used thedata for input energy and output energy to calculate Proteus’sefficiency for different flapping rates. These data are graphedin Figure 10. The scientists compared Proteus’s highest level ofefficiency with the average efficiency of a propeller-drivenboat. Look at the bar graph in Figure 10 to see if their datasupport their hypothesis—that penguin propulsion would bemore efficient than propeller propulsion.

This bar graph shows that Proteus is 17percent more efficient than a propeller-driven boat.

This line graph shows that Proteus was mostefficient when its foils were flapping about 1.7 times per second.

Chapter 116

Self-CheckWhat variable wereCzarnowski andTriantafyllou testing?(See page 724 to checkyour answer. )

Figure 10 Graphs of the Test Results

Flaps per second

Effic

ienc

y

0.7 1.2 1.7 2.2

70%

87%

Propeller-driven boat

Proteus


Draw ConclusionsAt the end of an investigation, you must draw a conclusion.You could conclude that your results supported your hypoth-esis, that your results did not support your hypothesis, or thatyou need more information. If you conclude that your resultssupport your hypothesis, you can ask further questions. If youconclude that your results do not support your hypothesis, youshould check your results or calcu-lations for errors. You may have tomodify your hypothesis or form anew one and conduct another inves-tigation. If you find that your resultsneither support nor disprove yourhypothesis, you may need to gathermore information, test your hypoth-esis again, or redesign the procedure.

The Proteus Conclusion AfterCzarnowski and Triantafyllou ana-lyzed the results of their test, theyconducted many more trials. Stillthey found that the penguinpropulsion system was more effi-cient than a propeller propulsionsystem. So they concluded thattheir hypothesis was supported,which led to more questions, as youcan see in Figure 11.

Communicate ResultsOne of the most important steps in any investigation is tocommunicate your results. You can write a scientific paper,make a presentation, or create a Web site. Telling otherswhat you learned is how science keeps going. Other scien-tists can conduct their own tests, modify your tests to learnsomething more specific, or study a new problem based onyour results.

Communicating About Proteus Czarnowski and Triantafylloupublished their results in academic papers, but they also dis-played their project and its results on the Internet. In addition,science magazines and newspapers have reported the work ofthese engineers. These reports allow you to conduct someresearch of your own about Proteus.


Figure 11 Could a penguin propulsion system be used on largeships, such as an oil tanker? The research continues!


Breaking the Mold of the Scientific MethodNot all scientists use the same scientific method, nor do theyalways follow the same steps in the same order. Why not?Sometimes you may have a clear idea about the question youwant to answer. Other times, you may have to revise yourhypothesis and test it again. While you should always take accu-rate measurements and record data correctly, you don’t alwayshave to follow the scientific method in a certain order. Figure 12shows you some other paths through the scientific method.

Building Scientific KnowledgeUsing the scientific method is a way to find answers to ques-tions and solutions to problems. But you should understand thatanswers are very rarely final answers. As our understanding ofscience grows, our understanding of the world around us changes.New ideas and new experiments teach us new things. Sometimes,however, an idea is supported again and again by many exper-iments and tests. When this happens, the idea can become atheory or even a law. As you will read on the next page, theo-ries and laws help to build new scientific knowledge.

Chapter 118

No

Yes

Draw Conclusions

Do they support your hypothesis?

MakeObservations Form a

Hypothesis

Test theHypothesis

Analyzethe Results

Ask a Question

CommunicateResults

Turn to page 33 to discover a tale of young Einstein’s

encounter with some otherscience heavyweights.

Figure 12 Scientific investiga-tions do not always proceed fromone step of the scientific methodto the next. Sometimes steps areskipped, and sometimes they arerepeated.


Scientific Theories You’ve probably heard a detectiveon a TV show say, “I’ve got a theory about who com-mitted the crime.” Does the detective have a scientifictheory? Probably not; it might be just a guess. A sci-entific theory is more complex than a simple guess.

In science, a theory is a unifying explanation fora broad range of hypotheses and observations thathave been supported by testing. A theory not onlycan explain an observation you’ve made but also canpredict an observation you might make in the future.Keep in mind that theories, like the one shown in Figure 13, can be changed or replaced as new observationsare made or as new hypotheses are tested.

Scientific Laws What do you think of when you hear theword law? Traffic laws? Federal laws? Well, scientific laws arenot like these laws. Scientific laws are determined by nature,and you can’t break a scientific law!

In science, a law is a summary of many experimental resultsand observations. A law tells you how things work. Laws arenot the same as theories because laws only tell you what hap-pens, not why it happens, as shown in Figure 14. Although alaw does not explain why something happens, the law tellsyou that you can expect the same thing to happen every time.

1. Name the steps that can be used in the scientific method.

2. How is a theory different from a hypothesis?

3. Analyzing Ideas Describe how our knowledge of sciencechanges over time.


Figure 14 Dropping a ball illustrates the law of conservation of energy. Although the ball doesn’t bounce back to its original height, energy is notlost—it is transferred to the ground.

REVIEW

WPS-P01-029-P

Figure 13 According to the big-bang theory, the universe wasonce a small, hot, and dense vol-ume of matter. About 10 to 20billion years ago, an event calledthe big bang sent matter in alldirections, forming the galaxiesand planets.

NSTA

TOPIC: The Scientific MethodGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP010

Examples of Models

Chapter 120

Using Models in Physical ScienceThink again about Proteus. How much like a penguin was it?Well, Proteus didn’t have feathers and wasn’t a living thing,but its “flippers” were designed to create the same kind ofmotion as a penguin’s flippers. The MIT engineers built Proteusto mimic the way a penguin swims so that they could gain agreater understanding about boat propulsion. In other words,they created a model.

What Is a Model?A model is a representation of an object or system. Models areused in science to describe or explain certain characteristics ofthings. Models can also be used for making predictions andexplaining observations. A model is never exactly like the realobject or system—if it were, it would no longer be a model.Models are particularly useful in physical science because manycharacteristics of matter and energy can be either hard to seeor difficult to understand. You can see some examples of sci-entific models below.

Section

3

model

Explain how models representreal objects or systems.

Give examples of different waysmodels are used in science.

You can’t see the tinyparts that make up matter, but you canmake a model thatshows how the parts fit together.

A cell diagram is amodel that lets youlook at all the parts ofa cell up close—withoutusing a microscope.

A model of a building can be designed on acomputer before moneyis spent constructingthe actual building.

A model rocket is muchsmaller than a real rocket,but launching one in yourbackyard can help youunderstand how real rock-ets blast off into space.



Models for Weather Forecasting

You’ve probably seen a weather report on television. Thinkabout the models that a weather reporter uses to tell youabout the weather: satellite pictures, color-coded maps,and live radar images. How are these models used torepresent the weather? Why do you think that sometimesweather forecasts are wrong?

Models Help You Visualize InformationWhen you’re trying to learn about something that you can’tsee or observe directly, a model can help you visualize it, orpicture it in your mind. Familiar objects or ideas can help youunderstand something a little less familiar.

Objects as Models When you use an objectas a model for something you cannot see, theobject must have characteristics similar tothose of the real thing. For example, a coiledspring toy is often used as a model of soundwaves. You’ve probably used this kind ofspring toy before, so it’s a familiar object.Sound waves are probably a little less famil-iar—after all, you can’t see them. But thespring toy behaves a lot like sound waves do.So using the spring toy as a model, as shownin Figure 15, can make the behavior of soundwaves easier to understand.

Ideas as Models When you’re trying tounderstand something but don’t have anobject to use as a model, you can create amodel from an idea. For example, when sugardissolves in iced tea, it seems to disappear. Totry to understand where the sugar goes, imag-ine a single drop of tea magnified until it isalmost as big as you are, with tiny spacesbetween the particles of water in the tea.Using this model, as shown in Figure 16, youcan understand that the sugar seems to dis-appear because the sugar particles fit intospaces between the water particles in the tea.


Figure 15 A coiled spring toy can show youhow air particles crowd together in parts ofa sound wave.

Figure 16 Just by imagining a big drop oftea, you are creating a model!


Models Are Just the Right SizeHow can you observe how the phases of the moon occur?That’s a tough problem, because you’re on Earth and you can’teasily get off of the Earth to observe the moon going aroundit. But you can observe a model of the moon, Earth, and sun,as shown in Figure 17. As you can see, models can representthings that are too large to easily observe.

Models are also useful for under-standing things that are too small to

see. For example, you can tell just bylooking that a grain of salt has a definite

shape, but you may not know why. A modelof the structure of salt, as shown in Figure 18,

can help you understand how the arrangementof tiny particles accounts for its shape.

Models Build Scientific KnowledgeModels not only can represent scientific ideas and objects butalso can be tools that you can use to conduct investigationsand illustrate theories.

Testing Hypotheses The MIT engineers were trying to testtheir hypothesis that a boat that mimics the way a penguinswims would be more efficient than a boat powered by pro-pellers. How did they test this hypothesis? By building a model,Proteus. When using the scientific method to develop newtechnology, testing a hypothesis often requires building amodel. By conducting tests with Proteus, the MIT engineerstested their hypothesis and found out what factors affectedthe model’s efficiency. Using the data they collected, theycould consider building a full-sized penguin boat.

Chapter 122

Figure 17 Using this model, you can seehow the Earth’s rotation, in addition to themoon’s revolution around the Earth as theEarth revolves around the sun, results inthe different phases of the moon.

Build a model car and test itsspeed on page 627 in the

LabBook.

Figure 18 The particles of matter in a grain of salt connect in a continuous pattern that forms a cube. That’s why a grain of salt has a cubic shape.


Illustrating Theories Recall that a theory explainswhy things happen the way they do. Sometimes,however, a theory is hard to picture. That’s wheremodels come in handy. A model is different froma theory, but a model can present a picture of whatthe theory explains when you cannot actually observeit. You can see an example of this in Figure 19.

Models Can Save Time and MoneyWhen creating technology, scientists often create a model firstso that they can test its characteristics and improve its designbefore building the real thing. You may recall that Proteus wasn’tbig enough to carry even a single passenger. Why didn’t theMIT engineers begin by building a full-sized boat? Imagine ifthey had gone to all that trouble and found out that theirdesign didn’t work. What a waste! Models allow you to testideas without having to spend the time and money necessaryto make the real thing. In Figure 20, you can see another exam-ple of how models save time and money.

1. What is the purpose of a model?

2. Give three examples of models that you see every day.

3. Interpreting Models Both a globe and a flat world mapmodel certain features of the Earth. Give an example ofwhen you would use a globe and an example of whenyou would use a flat map.

Figure 20 Car engineers canconduct cyber-crashes, in whichcomputer-simulated cars crashin various ways. Engineers usethe results to determine whichsafety features to install on thecar—all without damaging a single automobile.


REVIEW

Figure 19 This model illustratesthe atomic theory, which statesthat all matter is made of tinyparticles called atoms.

NSTA

TOPIC: Using Models in Physical Science

GO TO: www.scilinks.orgsciLINKS NUMBER: HSTP015

Chapter 124

Measurement and Safety inPhysical ScienceHundreds of years ago, different countries used different sys-tems of measurement. In England, the standard for an inchused to be three grains of barley placed end to end. Otherstandardized units of the modern English system, which isused in the United States, used to be based on parts of thebody, such as the foot. Such units were not very accuratebecause they were based on objects that varied in size.

Eventually people recognized that there was a need for asingle measurement system that was simple and accurate. Inthe late 1700s, the French Academy of Sciences began todevelop a global measurement system, now known as theInternational System of Units, or SI.

The International System of UnitsToday most scientists in almost all countries use the InternationalSystem of Units. One advantage of using SI measurements isthat it helps scientists share and compare their observations andresults. Another advantage of SI is that all units are based onthe number 10, which makes conversions from one unit toanother easy to do. The table in Figure 21 contains the com-monly used SI units for length, volume, mass, and temperature.

Common SI Units

Figure 21 Prefixes are usedwith SI units to convert themto larger or smaller units. Forexample kilo means 1,000times, and milli indicates1/1,000 times. The prefix useddepends on the size of theobject being measured.

Length

Volume

Mass

Temperature

meter (m)kilometer (km)decimeter (dm)centimeter (cm)millimeter (mm)micrometer (µm)nanometer (nm)

cubic meter (m3)cubic centimeter (cm3)liter (L)milliliter (mL)

kilogram (kg)gram (g)milligram (mg)

Kelvin (K)Celsius (C)

1 km 1,000 m1 dm 0.1 m1 cm 0.01 m1 mm 0.001 m1 µm 0.000 001 m1 nm 0.000 000 001 m

1 cm3 0.000 001 m3

1 L 1 dm3 0.001 m3

1 mL 0.001 L 1 cm3

1 g 0.001 kg1 mg 0.000 001 kg

0C 273 K100C 373 K

Section

4

meter temperaturevolume areamass density

Explain the importance of theInternational System of Units.

Determine the appropriate units to use for particular measurements.

Describe how area and densityare derived quantities.


Length How long is an Olympic-sized swimming pool? Todescribe its length, a physical scientist would use meters (m),the basic SI unit of length. Other SI units of length are largeror smaller than the meter by multiples of 10. For example, 1 kilometer (km) equals 1,000 meters. If you divide 1 m into1,000 parts, each part equals 1 mm. This means that 1 mm isone-thousandth of a meter. Although that seems pretty small,some objects are so tiny that even smaller units must be used.To describe the length of a grain of salt, micrometers (m) ornanometers (nm) are used.

Volume Imagine that you need to move some lenses to alaser laboratory. How many lenses will fit into a crate? Thatdepends on the volume of the crate and the volume of eachlens. Volume is the amount of space that something occupies.

Volumes of liquids are expressed in liters (L). Liters arebased on the meter. A cubic meter (1 m3) is equal to 1,000 L.So 1,000 L will fit into a box 1 m on each side. A milliliter(mL) will fit into a box 1 cm on each side. So 1 mL = 1 cm3.Graduated cylinders are used to measure the volume of liquids.

Volumes of solid objects are expressed in cubic meters (m3).Volumes of smaller objects can be expressed with cubic cen-timeters (cm3) or cubic millimeters (mm3). To find the volumeof a crate, or any other rectangular shape, multiply the lengthby the width by the height. To find the volume of an irregu-larly shaped object, measure how much liquid that object dis-places. You can see how this works in Figure 22.

Figure 22 When the rock is added, the water level rises from 70 mL to 80 mL. Because the rock displaces 10 mL of water, andbecause 1 mL = 1 cm3, the volume of the rock is 10 cm3.


a b

70 mL 80 mL

Pick an object to use as aunit of measure. It could be apencil, your hand, or anythingelse. Find how many unitswide your desk is, and com-pare your measurement withthose of your classmates.What were some of the unitsthat your classmates used?


Mass How many cars can a bridge support? That depends onthe strength of the bridge and the mass of the cars. Mass isthe amount of matter that something is made of. The kilo-gram (kg) is the basic SI unit for mass and would be used toexpress the mass of a car. Grams (one-thousandth of a kilo-

gram) are used to express the mass of smallobjects. A medium-sized apple has a massof about 100 g. Masses of very large objectsare expressed in metric tons. A metric tonequals 1,000 kg.

Temperature How hot is melted iron? Toanswer this question, a physical scientistwould measure the temperature of the liq-uid metal. Temperature is a measure of howhot (or cold) something is. You are prob-ably used to expressing temperature withdegrees Fahrenheit (F). Scientists often usedegrees Celsius (C), but the kelvin (K) is theSI unit for temperature. The thermometer inFigure 23 compares F with C, the unit youwill most often see in this book.

Derived QuantitiesSome quantities are formed from combinations of other meas-urements. Such quantities are called derived quantities. Botharea and density are derived quantities.

Area How much carpet would cover the floor of your class-room? It depends on the area of the floor. Area is a measureof how much surface an object has. To calculate the area of arectangular surface, measure the length and width, then usethis equation:

Area length width

The units for area are called square units, such as m2, cm2,and km2. The area of the rectangle in Figure 24 is 20 cm2.

Figure 24 If you count thesmaller squares within therectangle, you’ll count 20squares that each measure1 cm2.

Chapter 126

Figure 23 Measuring Temperature

212°F 100°CWater boils Water boils

98.6°F 37°CNormal body Normal bodytemperature temperature

32°F 0°CWater freezes Water freezes

Using Area to Find VolumeArea can be used to find thevolume of an object accord-ing to the following equation:

Volume Area height

1. What is the volume of abox 5 cm tall whose lidhas an area of 9 cm2?

2. A crate has a volume of 48 m3. The area of its bot-tom side is 16 m2. What isthe height of the crate?

3. A cube with a volume of8,000 cm3 has a height of20 cm. What is the area ofone of its sides?

MATH BREAK

˚F ˚C

-20

110

-100

020406080

100120140160180200220

102030405060708090100

5 cm

4 cm


Density Another derived quantity is density. Density is massper unit volume. So an object’s density is the amount of mat-ter it has in a given space. To find density (D), first measuremass (m) and volume (V ). Then use the following equation:

D mV

For example, suppose you want to know the density of the gear shown at right. Its mass is 75 g and its volume is 20 cm3. You can calculate the gear’s density like this:

D mV

75 g

20 cm3 3.75 g/cm3

Safety Rules!Physical science is exciting and fun, but it can also be dan-gerous. So don’t take any chances! Always follow your teacher’sinstructions, and don’t take shortcuts—even when you thinkthere is little or no danger.

Before starting an experiment, get your teacher's permis-sion and read the lab procedures carefully. Pay particular atten-tion to safety information and caution statements. The chartbelow shows the safety symbols used in this book. Get to knowthese symbols and what they mean by reading the safety infor-mation on page 622. This is important! If you are still unsureabout what a safety symbol means, ask your teacher.


Stay on the safe side by readingthe safety information on page622. You must do this beforedoing any experiment!

1. Why is SI important?

2. Which SI unit would you use to express the height ofyour desk? Which SI unit would you use to express thevolume of this textbook?

3. Comparing Concepts How is area different from volume?

REVIEW

Safety Symbols

Eye protection

Heating safety

Chemical safety

Clothing protection

Electric safety

Animal safety

Hand safety

Sharp object

Plant safety

NSTA

TOPIC: SI UnitsGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP020


Chapter Highlights

Chapter 128

SECTION 1 SECTION 2

Vocabularyphysical science (p. 7)

Section Notes

• Science is a process of mak-ing observations and askingquestions about thoseobservations.

• Physical science is the studyof matter and energy and isoften divided into physicsand chemistry.

• Physical science is part of many other areas of science.

• Many different careersinvolve physical science.

Vocabularyscientific method (p. 11)

technology (p. 11)

observation (p. 12)

hypothesis (p. 14)

data (p. 16)

theory (p. 19)

law (p. 19)

Section Notes

• The scientific method is aseries of steps that scientistsuse to answer questions andsolve problems.

• Any information you gatherthrough your senses is anobservation. Observationsoften lead to questions orproblems.

• A hypothesis is a possibleexplanation or answer to aquestion. A good hypothesisis testable.

• After you test a hypothesis,you should analyze yourresults and draw conclusionsabout whether your hypothe-sis was supported.

• Communicating your find-ings allows others to verifyyour results or continue toinvestigate your problem.

• A scientific theory is theresult of many investigationsand many hypotheses.Theories can be changed ormodified by new evidence.

• A scientific law is a summaryof many experimental resultsand hypotheses that havebeen supported over time.

LabsExploring the Unseen (p. 626)

Skills CheckVisual UnderstandingSCIENTIFIC METHOD To answer a question in science, you can use the scientific method.Review the flowchart on page 18 to see that thescientific method does not have to follow aspecific order.

MODELS A model is a representation of an object or system.Look back at the exampleson page 20 to learn moreabout different models.

Math ConceptsAREA To calculate the area of a rectangular surface, first measure its length and width, thenmultiply those values. The area of a piece ofnotebook paper with a length of 28 cm and awidth of 21.6 cm can be calculated as follows:

Area length width

28 cm 21.6 cm

604.8 cm2


Visit the National Science Teachers Association on-line Website for Internet resources related to this chapter. Just type inthe sciLINKS number for more information about the topic:

TOPIC: Matter and Energy sciLINKS NUMBER: HSTP005

TOPIC: The Scientific Method sciLINKS NUMBER: HSTP010

TOPIC: Using Models in Physical Science sciLINKS NUMBER: HSTP015

TOPIC: SI Units sciLINKS NUMBER: HSTP020

GO TO: go.hrw.com GO TO: www.scilinks.org

Visit the HRW Web site for a variety oflearning tools related to this chapter. Just type in the keyword:

KEYWORD: HSTWPS

29The World of Physical Science

SECTION 3 SECTION 4

Vocabularymodel (p. 20)

Section Notes

• Scientific models arerepresentations of objects orsystems. Models makedifficult concepts easier tounderstand.

• Models can represent thingstoo small to see or too largeto observe directly.

• Models can be used to testhypotheses and illustratetheories.

LabsOff to the Races! (p. 627)

Vocabularymeter (p. 25)

volume (p. 25)

mass (p. 26)

temperature (p. 26)

area (p. 26)

density (p. 27)

Section Notes

• The International System ofUnits is the standard systemof measurement used by sci-entists around the world.

• Length, volume, mass, andtemperature are quantities ofmeasurement. Each quantityof measurement is expressedwith a particular SI unit.

• Area is a measure of howmuch surface an object has.Density is a measure of massper unit volume.

• Safety rules are importantand must be followed at alltimes during scientificinvestigations.

LabsMeasuring Liquid Volume (p. 628)

Coin Operated (p. 629)


Chapter ReviewUSING VOCABULARY

For each pair of terms, explain the differencein their meanings.

1. science/technology

2. observation/hypothesis

3. theory/law

4. model/theory

5. volume/mass

6. area/density

UNDERSTANDING CONCEPTS

Multiple Choice

7. Physical science is the study of a. matter and motion.b. matter and energy.c. energy and motion.d. matter and composition.

8. 10 m is equal to a. 100 cm. c. 10,000 mm.b. 1,000 cm. d. Both (b) and (c)

9. For a hypothesis to be valid, it must be a. testable.b. supported by evidence.c. made into a law.d. Both (a) and (b)

10. The statement “Sheila has a stain on her shirt” is an exampleof a(n) a. law.b. hypothesis.c. observation.d. prediction.

11. A hypothesis is often developed out of a. observations. c. laws.b. experiments. d. Both (a) and (b)

12. How many milliliters are in 3.5 kL? a. 3,500 c. 3,500,000b. 0.0035 d. 35,000

13. A map of Seattle is an example of a a. law. c. model.b. quantity. d. unit.

14. Which of the following is an example oftechnology? a. massb. physical sciencec. screwdriverd. none of the above

Short Answer

15. Name two areas of science other thanchemistry and physics, and describe howphysical science has a role in those areasof science.

16. Explain why the results of one experimentare never really final results.

17. Explain why area and density are calledderived quantities.

18. If a hypothesis is not testable, does thatmean that it is wrong? Explain.

Concept Mapping

19. Use the following terms to create aconcept map: science, scientificmethod, hypothesis,problems, questions,experiments,observations.


MATH IN SCIENCE

24. The cereal box at right has a mass of 340 g. Its dimensions are 27 cm 19 cm 6 cm.a. What is the volume

of the box?b. What is its density?c. What is the area of

the front side of the box?

INTERPRETING GRAPHICS

Examine the picture below, and answer thequestions that follow:

25. How similar to the real object is thismodel?

26. What characteristics of the real objectdoes this model not show?

27. Why might this model be useful?

CRITICAL THINKING AND PROBLEM SOLVING

20. A tailor is someone who makes or altersitems of clothing. Why might a standardsystem of measurement be helpful to atailor?

21. Two classmates are having a debate aboutwhether a spatula is an example of tech-nology. Using what you know about sci-ence, technology, and spatulas, write acouple of sentences that will help yourclassmates settle their debate.

22. Imagine that you are conducting anexperiment in which you are testing theeffects of the height of a ramp on thespeed at which a toy car goes down theramp. What is the variable in this experi-ment? What factors must be controlled?

23. Suppose a classmate says, “I don’t need to study physical science because I’m notgoing to be a scientist, and scientists arethe only people who use physical sci-ence.” How would you respond? (Hint: In your answer, give several examples ofcareers that use physical science.)


Take a minute to reviewyour answers to the Pre-Reading Questionsfound at the bottom

of page 4. Have your answers changed? If necessary, revise your answers based on whatyou have learned since you began this chapter.

ReadingCheck-up


32

T he white light we see every day is actually composed of allthe colors of the spectrum. A laser emits a very small portion

of this spectrum. That is why there are blue lasers, red lasers, andso on. High-voltage sources called laser “pumps” cause lasermaterials to emit certain wavelengths of light, depending on thematerial used. A laser material, such as helium neon gas, emitsradiation (light) as a result of changes in the electron energylevels of its atoms. This process gives lasers their name: LightAmplification of the Stimulated Emission of Radiation.

Using Scientific ModelsJulie Williams-Byrd uses scientific models to predict the nature ofdifferent aspects of laser design. Different laser materials emitradiation at different wavelengths, and specific pump sourcesmust be used to induce “lasing.” “Researchers at LSB use lasermodels to predict output energy, wavelength, efficiency, and ahost of other properties of the laser system,” Williams-Byrd says.

New TechnologiesHer most challenging project has been building a laser-transmitter that will be used to measure winds in the atmos-phere. This system, called Lidar, is very much like radar exceptthat it uses light waves instead of sound waves to bounce offobjects. To measure winds, a laser beam is transmitted into theatmosphere, where it illuminates particles. A receiver looks atthese particles over a period of time and determines the changes

Julie Williams-Byrd uses her knowledge of physics todevelop better lasers. Shestarted working with lasers as a graduate student atHampton University, inVirginia. Today Williams-Byrdworks as an electronics engi-neer in the Laser SystemsBranch (LSB) of NASA. Shedesigns and builds lasers thatare used to monitor phenom-ena in the atmosphere, such as wind and ozone.

ELECTRON ICS ENG INEER

in position of the particles. Wind velocity is then determinedfrom this information. This new technology is expected to beused in a space shuttle mission called Sparcle.

Lasers All Around UsAlthough Williams-Byrd works with high-tech lasers, shepoints out that lasers are a part of daily life for manypeople. For example, lasers are used in scanners at manyretail stores. Ophthalmologists use lasers to correct near-sightedness. Some metal workers use them to cut metal.And lasers are even used to create spectacular light shows!

Going Further Can you think of any new uses for lasers? Make a list inyour ScienceLog, and then do some research to find out ifany of your ideas already exist.

Julie Williams-Byrd useslaser generators like thisone in her work at NASA.


33

“Inspiration”by Ben Bova

No matter where you are on the face ofthe Earth, you can pinpoint your loca-tion. Most of the time, you use map

coordinates, or latitude and longitude readings.And you can give your distance above sea level.With modern technology, you can give an accu-rate, three-dimensional description of whereyou are. But what about a fourth dimension?Consider for a moment traveling in time. Notjust getting through today and into tomorrowbut actually being able to leap back and forththrough time.

Novelist H. G. Wells imagined such a possi-bility in his novelette The Time Machine. Whenthe story was published in 1895, most physi-cists said that the notion of traveling in timewas nonsense and against all the laws ofphysics that govern the universe. The idea thattime was similar to length, width, or height wasfoolishness. Or so they thought.

It was up to Albert Einstein, in 1905, to pro-pose a different view of the universe. However,when Wells’s story was first published, Einsteinwas just 16 and not a very good student. Whatif Einstein had been discouraged and had notpursued his interest in physics? But Einstein didlook at the universe and maybe, just maybe, hehad an inspiration.

Ben Bova’s story “Inspiration” describes justsuch a possibility. Young Einstein meets Wellsand the great physicist of the time, Lord Kelvin.But was the meeting just a lucky coincidence or something else entirely? Escape to the Holt Anthology of Science Fiction, and read“Inspiration” to find out.


34 Chapter 2

What Is Matter? . . . . . . 36QuickLab . . . . . . . . . . . 36MathBreak . . . . . . . . . . 38Biology Connection. . . . 40Apply . . . . . . . . . . . . . . 42Internet Connect . . . . . 42

Describing Matter . . . . . 43MathBreak . . . . . . . . . . 45Apply . . . . . . . . . . . . . . 46QuickLab . . . . . . . . . . . 49Environment

Connection . . . . . . . . . 51Internet Connect . . . . . 51

Chapter Review . . . . . . . . . . 54

Feature Articles . . . . . . . 56, 57

LabBook . . . . . . . . . . . 630–635

The Propertiesof MatterThe Propertiesof Matter

Nice IceYou’ve seen water in many forms: steam rising from a kettle, dew collecting on grass, and tiny crystals of frostforming on the windows in winter. But no matter what itsform, water is still water. In this chapter, you’ll learn moreabout the many different properties of matter, such aswater. You’ll also learn about changes in matter that takeplace all around you.


1. What is matter? 2. What is the difference

between a physicalproperty and a chemicalproperty?

3. What is the differencebetween a physicalchange and a chemicalchange?


35

SACK SECRETSIn this activity, you will test yourskills in determining the identity ofan object based on its properties.

Procedure

1. You and two or three of yourclassmates will receive a sealedpaper sack containing a mysteryobject. Do not open the sack!

2. For 5 minutes, make as manyobservations as you can about theobject. You may touch, smell, orlisten to the object through thesack; shake the sack; and so on.Be sure to record yourobservations.

Analysis

3. At the end of 5 minutes, discussyour findings with your partners.

4. In your ScienceLog, list the object’sproperties. Make a conclusionabout the object’s identity.

5. Share your observations, your listof properties, and your conclusionwith the class. Now you are readyto open the sack.

6. Did you properly identify theobject? If so, how? If not, why not? Write your answers in yourScienceLog. Share them with the class.

The Properties of MatterCopyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 236

What Is Matter?Here’s a strange question: What doyou have in common with a toaster?

Give up? Okay, here’s anotherquestion: What do you have in com-mon with a steaming bowl of soup ora bright neon sign?

You are probably thinking these are trickquestions. After all, it is hard to imagine thata human—you—has anything in common witha kitchen appliance, some hot soup, or a glowingneon sign.

Everything Is Made of MatterFrom a scientific point of view you have at least one charac-teristic in common with these things. You, the toaster, thebowl, the soup, the steam, the glass tubing, and the glowinggas are all made of matter. But what is matter exactly? If somany different kinds of things are made of matter, you mightexpect the definition of the word matter to be complicated.But it is really quite simple. Matter is anything that has vol-ume and mass.

Matter Has VolumeAll matter takes up space. The amount of space taken up, oroccupied, by an object is known as the object’s volume. Thesun, shown in Figure 1, has volume because it takes up spaceat the center of our solar system. Your fingernails, the Statueof Liberty, the continent of Africa, and a cloud all have vol-ume. And because these things have volume, they cannotshare the same space at the same time. Even the tini-est speck of dust takes up space, and there’s noway another speck of dust can fit into thatspace without somehow bumping the firstspeck out of the way. Try the QuickLabon this page to see for yourself thatmatter takes up space.

Figure 1 The volume of the sunis about 1,000,000 (1 million)times larger than the volume ofthe Earth.

Section

1

matter gravityvolume weightmeniscus newtonmass inertia

Name the two properties of allmatter.

Describe how volume and massare measured.

Compare mass and weight. Explain the relationship between

mass and inertia.

Space Case

1. Crumple a piece of paper,and fit it tightly in thebottom of a cup so that itwon’t fall out.

2. Turn the cup upside down.Lower the cup straightdown into a large beakeror bucket half-filled withwater until the cup is allthe way underwater.

3. Lift the cup straight out ofthe water. Turn the cupupright and observe thepaper. Record your obser-vations in your ScienceLog.

4. Now punch a small hole in the bottom of the cupwith the point of a pencil.Repeat steps 2 and 3.

5. How do these results showthat air has volume?Record your explanation inyour ScienceLog.



Liquid Volume Lake Erie, the smallest of the Great Lakes, hasa volume of approximately 483,000,000,000,000 (483 trillion)liters of water. Can you imagine that much liquid? Well, thinkof a 2 liter bottle of soda. The water in Lake Erie could fillmore than 241 trillion of those bottles. That’s a lot of water!On a smaller scale, a can of soda has a volumeof only 355 milliliters, which is approximatelyone-third of a liter. You can read the volumeprinted on the soda can. Or you can checkthe volume by pouring the soda into a largemeasuring cup from your kitchen, as shownin Figure 2.

Measuring the Volume of Liquids In your sci-ence class, you’ll probably use a graduated cylinder tomeasure the volume of liquids. Keep in mind that thesurface of a liquid in a graduated cylinder is not flat.The curve that you see at the liquid’s surface has a spe-cial name—the meniscus (muh NIS kuhs). When youmeasure the volume of a liquid, you must look at thebottom of the meniscus, as shown in Figure 3. (A liquidin any container, including a measuring cup or a largebeaker, has a meniscus. The meniscus is just too flat to seein a wider container.)

Liters (L) and milliliters (mL) are the units used mostoften to express the volume of liquids. The volume of anyamount of liquid, from one raindrop to a can of soda to anentire ocean, can be expressed in these units.

The Properties of Matter 37

Figure 2 If the measurementis accurate, the volume

measured should bethe same as the

volume printedon the can.

The volume of a typicalraindrop is approximately0.09 mL, which means that it would take almost 4,000raindrops to fill a soda can.

Meniscus

Figure 3 To measure volume correctly, read the scale at thelowest part of the meniscus (as indicated) at eye level.


Solid Volume The volume of any solid object is expressedin cubic units. Cubic means “having three dimensions.” Onecubic unit, a cubic meter, is shown in Figure 4. In science,cubic meters (m3) and cubic centimeters (cm3) are the unitsmost often used to express the volume of solid items. The 3in these unit abbreviations shows that three quantities weremultiplied to get the final result. For a rectangular object, thesethree quantities are length, width, and height. Try this foryourself in the MathBreak at left.

Comparing Solid and Liquid Volumes Suppose you wantto determine whether the volume of an ice cube is equal tothe volume of water that is left when the ice cube melts.Because 1 mL is equal to 1 cm3, you can express the volumeof the water in cubic centimeters and compare it with the vol-ume of the ice cube. The volume of any liquid can be expressedin cubic units in this way. (However, in SI, volumes of solidsare never expressed in liters or milliliters.)

Measuring the Volume of Gases How do you measure thevolume of a gas? You can’t hold a ruler up to a gas, and youcan’t pour a gas into a graduated cylinder. So it’s impossible,right? Wrong! A gas expands to fill its container, so if youknow the volume of the container the gas is in, then youknow the volume of the gas.

Matter Has MassAnother characteristic of all matter is mass. Mass is the amountof matter that something is made of. For example, the Earthis made of a very large amount of matter and therefore hasa large mass. A peanut is made of a much smaller amount ofmatter and thus has a smaller mass. Remember, even some-thing as small as a speck of dust is made of matter and there-fore has mass.

38

Calculating VolumeA typical compact disc (CD)case has a length of 14.2 cm,a width of 12.4 cm, and aheight of 1.0 cm. The volumeof the case is the lengthmultiplied by the width multi-plied by the height:

14.2 cm 12.4 cm 1.0 cm 176.1 cm3

Now It’s Your Turn1. A book has a length of

25 cm, a width of 18 cm,and a height of 4 cm. Whatis its volume?

2. What is the volume of asuitcase with a length of95 cm, a width of 50 cm,and a height of 20 cm?

3. For additional practice, find the volume of otherobjects that have square orrectangular sides. Compareyour results with those ofyour classmates.

MATH BREAK

How would you measurethe volume of this

strangely shapedobject? To find out,

turn to page 630in the LabBook.

1m

1 m

1 m

Chapter 2

Figure 4 A cubic meterhas a height of 1 m, alength of 1 m, and a widthof 1 m, so its volume is 1 m 1 m 1 m 1 m3.1 m3


Is a Puppy Like a Bowling Ball? An object’smass can be changed only by changing theamount of matter in the object. Consider thebowling ball shown in Figure 5. Its mass is con-stant because the amount of matter in the bowlingball never changes (unless you use a sledgehammerto remove a chunk of it!). Now consider the puppy.Does its mass remain constant? No, because thepuppy is growing. If you measured the puppy’smass next year or even next week, you’d findthat it had increased. That’s because morematter—more puppy—would be present.

The Difference Between Mass and WeightWeight is different from mass. To understand this difference,you must first understand gravity. Gravity is a force of attrac-tion between objects that is due to their masses. This attrac-tion causes objects to exert a pull on other objects. Because allmatter has mass, all matter experiences gravity. The amount ofattraction between objects depends on two things—the massesof the objects and the distance between them, as shown inFigure 6.

Gravitational force is smaller between objects with smallermasses that are close together than between objects with largemasses that are close together (as shown in a).

An increase in distance reduces gravitational force between twoobjects. Therefore, gravitational force between objects with largemasses (such as those in a) is less if they are far apart.


Figure 6 How Mass and Distance Affect Gravity Between Objects

Gravitational force (represented by the width of the arrows) islarge between objects with large masses that are close together.

a

b

c

Figure 5 The mass of thebowling ball does notchange. The mass of thepuppy increases as morematter is added—that is, asthe puppy grows.

Imagine the following itemsresting side by side on atable: an elephant, a tennisball, a peanut, a bowling ball,and a housefly. In yourScienceLog, list these items inorder of their attraction tothe Earth due to gravity, fromleast to greatest amount ofattraction. Follow your listwith an explanation of whyyou arranged the items in theorder that you did.


May the Force Be with You Gravitational force is experi-enced by all objects in the universe all the time. But the ordi-nary objects you see every day have masses so small (relativeto, say, planets) that their attraction toward each other is hardto detect. Therefore, the gravitational force experienced byobjects with small masses is very slight. However, the Earth’smass is so large that the gravitational force between objects,such as our atmosphere or the space shuttle, and the Earth isgreat. Gravitational force is what keeps you and everything elseon Earth from floating into space.

So What About Weight? A measure of the gravitational forceexerted on an object is called weight. Consider the brick inFigure 7. The brick has mass. The Earth also has mass. Therefore,the brick and the Earth are attracted to each other. A force isexerted on the brick because of its attraction to the Earth. Theweight of the brick is a measure of this gravitational force.

Now look at the sponge in Figure 7.The sponge is the same size as the brick, but its mass is much less. Therefore, the

sponge’s attraction toward the Earth isnot as great, and the gravitational

force on the sponge is not as great.Thus, the weight of the sponge isless than the weight of the brick.

At a Distance The attractionbetween objects decreases as thedistance between them increases.As a result, the gravitational forceexerted on objects also decreases asthe distance increases. For this rea-son, a brick floating in space wouldweigh less than it does resting onEarth’s surface. However, the brick’smass would stay the same.

Massive Confusion Back on Earth, the gravitational forceexerted on an object is about the same everywhere, so anobject’s weight is also about the same everywhere. Becausemass and weight remain constant everywhere on Earth, theterms mass and weight are often used as though they meanthe same thing. But using the terms interchangeably can leadto confusion. So remember, weight depends on mass, butweight is not the same thing as mass.

Chapter 240


The mineral calcium is stored inbones, and it accounts for about 70percent of the mass of the humanskeleton. Calcium strengthens bones,helping the skeleton to remainupright against the strong force ofgravity pulling it toward the Earth.

Figure 7 This brick and sponge may be the same size, but their masses, and therefore their weights, arequite different.

Measuring Mass and WeightThe SI unit of mass is the kilogram (kg), but mass is oftenexpressed in grams (g) and milligrams (mg) as well. These unitscan be used to express the mass of any object, from a singlecell in your body to the entire solar system. Weight is a meas-ure of gravitational force and must be expressed in units offorce. The SI unit of force is the newton (N). So weight isexpressed in newtons.

A newton is approximately equal to the weight of a 100 gmass on Earth. So if you know the mass of an object, you cancalculate its weight on Earth. Conversely, if you know theweight of an object on Earth, you can determine its mass.Figure 8 summarizes the differences between mass and weight.


Mass is . . . a measure of the amount of

matter in an object.

always constant for an objectno matter where the object isin the universe.

measured with a balance(shown below).

expressed in kilograms (kg),grams (g), and milligrams (mg).

Weight is . . . a measure of the gravitational

force on an object.

varied depending on wherethe object is in relation to theEarth (or any other large bodyin the universe).

measured with a spring scale(shown above).

expressed in newtons (N).

Figure 8 Differences Between Mass and Weight

Self-CheckIf all of your schoolbooks combined havea mass of 3 kg, what istheir total weight innewtons? Rememberthat 1 kg = 1,000 g.(See page 724 to checkyour answer.)



Mass Is a Measure of InertiaImagine trying to kick a soccer ball that has the mass of a

bowling ball. It would be painful! The reason has to dowith inertia (in UHR shuh). Inertia is the tendency of

all objects to resist any change in motion. Because ofinertia, an object at rest will remain at rest untilsomething causes it to move. Likewise, a movingobject continues to move at the same speed andin the same direction unless something acts on itto change its speed or direction.

Mass is a measure of inertia because an objectwith a large mass is harder to start in motion andharder to stop than an object with a smaller mass.

This is because the object with the large mass hasgreater inertia. For example, imagine that you are

going to push a grocery cart that has only one potatoin it. No problem, right? But suppose the grocery cart

is filled with potatoes, as in Figure 9. Now the total mass—and the inertia—of the cart full of potatoes is much greater.

It will be harder to get the cart moving and harder to stopit once it is moving.

1. What are the two properties of all matter?

2. How is volume measured? How is mass measured?

3. Analyzing Relationships Do objects with large massesalways have large weights? Explain your reasoning.

Chapter 242

Mass, Weight, and Bathroom Scales

Ordinary bathroom scales are spring scales. Many scalesavailable today show a reading in both pounds (a com-mon, though not SI, unit of weight) and kilograms. Howdoes such a reading contribute to the confusionbetween mass and weight?

REVIEW

Figure 9 Why is a cartload ofpotatoes harder to get movingthan a single potato? Because of inertia, that’s why!

NSTA

TOPIC: What Is Matter?GO TO: www.scilinks.orgsciLINKS NUMBER: HSTP030



Describing MatterHave you ever heard of the game called “20 Questions”? Inthis game, your goal is to determine the identity of an objectthat another person is thinking of by asking questions aboutthe object. The other person can respond with only a “yes”or a “no.” If you can identify the object after asking 20 orfewer questions, you win! If you still can’t figure out the object’sidentity after asking 20 questions, you may not be asking theright kinds of questions.

What kinds of questions should you ask? You might findit helpful to ask questions about the properties of the object.Knowing the properties of an object can help you determinethe object’s identity, as shown below.

Physical PropertiesSome of the questions shown above help the asker gatherinformation about color (Is it orange?), odor (Does it have anodor?), and mass and volume (Could I hold it in my hand?).Each of these properties is a physical property of matter. Aphysical property of matter can be observed or measured with-out changing the identity of the matter. For example, youdon’t have to change what the apple is made of to see that itis red or to hold it in your hand.

Could I hold it in my hand?

Yes.

Does it have an odor? Yes.

Is it safeto eat?

Yes.

Yes.Is it anapple?

No. No. Yes.

Is it orange?Yellow? Red?

With a partner, play a gameof 20 Questions. One personwill think of an object, andthe other person will askyes/no questions about it.Write the questions in yourScienceLog as you go along.Put a check mark next to thequestions asked about physi-cal properties. When theobject is identified or whenthe 20 questions are up,switch roles. Good luck!

Section

2

physical property physical changedensity chemical changechemical property

Give examples of matter’s differ-ent properties.

Describe how density is used toidentify different substances.

Compare physical and chemicalproperties.

Explain what happens to matterduring physical and chemicalchanges.


Physical Properties Identify Matter You rely on physicalproperties all the time. For example, physical properties helpyou determine whether your socks are clean (odor), whetheryou can fit all your books into your backpack (volume), orwhether your shirt matches your pants (color). The table belowlists some more physical properties that are useful in describ-ing or identifying matter.

Spotlight on Density Density is a very helpful propertywhen you need to distinguish different substances. Look

at the definition of density in the table above—mass per unit volume. If you think back to

what you learned in Section 1, you candefine density in other terms: density isthe amount of matter in a given space,or volume, as shown in Figure 10.

44

Definition

the ability to transferthermal energy fromone area to another

the physical form inwhich a substanceexists, such as a solid,liquid, or gas

the ability to bepounded into thinsheets

the ability to be drawnor pulled into a wire

the ability to dissolve in another substance

mass per unit volume

Example

Plastic foam is a poorconductor, so hotchocolate in a plastic-foam cup will not burnyour hand.

Ice is water in its solidstate.

Aluminum can berolled or pounded intosheets to make foil.

Copper is often used to make wiring.

Sugar dissolves in water.

Lead is used to makesinkers for fishing linebecause lead is moredense than water.

Physical property

Thermal conductivity

State

Malleability (MAL ee uh BIL uh tee)

Ductility(duhk TIL uh tee)

Solubility(SAHL yoo BIL uh tee)

Density

Chapter 2

More Physical Properties

Figure 10 A golf ballis more dense thana table-tennis ballbecause the golf ball contains morematter in a similar volume.


To find an object’s density (D), first measure its mass (m)and volume (V). Then use the following equation:

D = mV

Units for density are expressed using a mass unit divided bya volume unit, such as g/cm3, g/mL, kg/m3, and kg/L.

Using Density to Identify Substances Density is a usefulproperty for identifying substances for two reasons. First, thedensity of a particular substance is always the same at a givenpressure and temperature. For example, the helium in a hugeairship has a density of 0.0001663 g/cm3 at 20C and normalatmospheric pressure. You can calculate the density of anyother sample of helium at that same temperature and pres-sure—even the helium in a small balloon—and you will get0.0001663 g/cm3. Second, the density of one substance is usu-ally different from that of another substance. Check out thetable below to see how density varies among substances.

Do you remember your imaginaryattempt at gold prospecting? To makesure you hadn’t found more fool’sgold (iron pyrite), you could comparethe density of a nugget from yoursample, shown in Figure 11, with theknown densities for gold and ironpyrite at the same temperature andpressure. By comparing densities,you’d know whether you’d actuallystruck gold or been fooled again.


DensityYou can rearrange the equa-tion for density to find massand volume as shown below:

D mV

m D V V mD

1. Find the density of a sub-stance with a mass of 5 kgand a volume of 43 m3.

2. Suppose you have a leadball with a mass of 454 g.What is its volume? (Hint:Use the table at left.)

3. What is the mass of a 15 mL sample of mercury?(Hint: Use the table at left.)

MATH BREAK

Pennies minted before 1982are made mostly of copperand have a density of 8.85 g/cm3. In 1982, apenny’s worth of copperbegan to cost more thanone cent, so the U.S.Department of the Treasurybegan producing penniesusing mostly zinc with acopper coating. Penniesminted after 1982 have adensity of 7.14 g/cm3.Check it out for yourself!

Density*Substance (g/cm3)

Helium (gas) 0.00001663

Oxygen (gas) 0.001331

Water (liquid) 1.00

Iron pyrite (solid) 5.02

Zinc (solid) 7.13

Density*Substance (g/cm3)

Copper (solid) 8.96

Silver (solid) 10.50

Lead (solid) 11.35

Mercury (liquid) 13.55

Gold (solid) 19.32

Figure 11 Did youfind gold or fool’s gold?

Density(g/cm3)

0.0001663

0.001331

1.00

5.02

7.13

Density(g/cm3)

8.96

10.50

11.35

13.55

19.32

* at 20C and normal atmospheric pressure

Densities of Common Substances*

Mass = 96.6 gVolume = 5.0 cm3


Density and Grease Separators

The grease separator shown here is a kitchen device that cooks use tocollect the best meat juices for makinggravies. Based on what you know about density, describe how a grease separator works. Be sure to explain why the spout is at the bottom.

Liquid Layers What do you think causes the liquid inFigure 12 to look the way it does? Is it magic? Is it trickphotography? No, it’s differences in density! There are actu-ally four different liquids in the jar. Each liquid has a differ-ent density. Because of these differences in density, the liquidsdo not mix together but instead separate into layers, with thedensest layer on the bottom and the least dense layer on top.The order in which the layers separate helps you determinehow the densities of the liquids compare with one another.

The Density Challenge Imagine that you could put a lid onthe jar in the picture and shake up the liquids. Would the dif-ferent liquids mix together so that the four colors would blendinto one interesting color? Maybe for a minute or two. But ifthe liquids are not soluble in one another, they would startto separate, and eventually you’d end up with the same four layers.

The same thing happens when you mix oil and vinegar tomake salad dressing. When the layers separate, the oil is ontop. But what do you think would happen if you added moreoil? What if you added so much oil that there was severaltimes as much oil as there was vinegar? Surely the oil wouldget so heavy that it would sink below the vinegar, right? Wrong!No matter how much oil you have, it will always be less densethan the vinegar, so it will always rise to the top. The sameis true of the four liquids shown in Figure 12. Even if you addmore yellow liquid than all of the other liquids combined, allof the yellow liquid will rise to the top. That’s because den-sity does not depend on how much of a substance you have.

Chapter 246

REVIEW

1. List three physical prop-erties of water.

2. Why does a golf ball feelheavier than a table-tennisball?

3. Describe how you can deter-mine the relative densitiesof liquids.

4. Applying Concepts Howcould you determine thata coin is not pure silver?

Figure 12 The yellow liquid isthe least dense, and the greenliquid is the densest.

Chemical PropertiesPhysical properties are not the only properties that describematter. Chemical properties describe a substance based on itsability to change into a new substance with different proper-ties. For example, a piece of wood can be burned to createnew substances (ash and smoke) with properties different fromthe original piece of wood. Wood has the chemical propertyof flammability—the ability to burn. A substance that does notburn, such as gold, has the chemical property of nonflamma-bility. Other common chemical properties include reactivitywith oxygen, reactivity with acid, and reactivity with water.(The word reactivity just means that when two substances gettogether, something can happen.)

Observing Chemical Properties Chemical properties can beobserved with your senses. However, chemical properties aren’tas easy to observe as physical properties. For example, you canobserve the flammability of wood only while the wood is burn-ing. Likewise, you can observe the nonflammability of goldonly when you try to burn it and it won’t burn. But a sub-stance always has its chemical properties. A piece of wood isflammable even when it’s not burning.

Some Chemical Properties of Car Maintenance Look atthe old car shown in Figure 13. Its owner calls it Rust Bucket.Why has this car rusted so badly while some other cars thesame age remain in great shape? Knowing about chemicalproperties can help answer this question.

Most car bodies are made from steel, which is mostly iron. Iron has many desirable physicalproperties, including strength, malleability,and a high melting point. Iron also hasmany desirable chemical properties,including nonreactivity with oil andgasoline. All in all, steel is a goodmaterial to use for car bodies. It’s notperfect, however, as you can proba-bly tell from the car shown here.

Figure 13 Rust BucketOne unfavorable chemical property of iron is its reactivitywith oxygen. When iron isexposed to oxygen, it rusts.

The Properties of Matter 47Copyright © by Holt, Rinehart and Winston. All rights reserved.

This bumper is rust free because it is coated with a barrier ofchromium, which is nonreactivewith oxygen.

Paint doesn’t react withoxygen, so it provides abarrier between oxygen and the iron in the steel.

This hole started as a small chip in thepaint. The chipexposed the iron in the car’s body tooxygen. The ironrusted and eventuallycrumbled away.


Physical Vs. Chemical PropertiesYou can describe matter by both physical and chemical prop-

erties. The properties that are most useful in identifying asubstance, such as density, solubility, and reactivity

with acids, are its characteristic properties. Thecharacteristic properties of a substance are always

the same whether the sample you’re observ-ing is large or small. Scientists rely on char-acteristic properties to identify and classifysubstances. Figure 14 describes some physi-cal and chemical properties.

It is important to remember the differencesbetween physical and chemical properties. For

example, you can observe physical propertieswithout changing the identity of the substance.

You can observe chemical properties only in situationsin which the identity of the substance could change.

Physical Changes Don’t Form New SubstancesA physical change is a change that affects one or more physi-cal properties of a substance. For example, if you break a pieceof chalk in two, you change its physical properties of size andshape. But no matter how many times you break it, chalk isstill chalk. The chemical properties of the chalk remainunchanged. Each piece of chalk would still produce bubbles ifyou placed it in vinegar.

Chapter 248

Helium is used in airshipsbecause it is less dense thanair and is nonflammable.

If you add bleach to waterthat is mixed with red foodcoloring, the red color willdisappear.

Figure 14 Substances havedifferent physical and chemicalproperties.

a

b

Substance Physical property Chemical property

Helium less dense than air nonflammable

Wood grainy texture flammable

Baking soda white powder reacts with vinegar to produce bubbles

Powdered sugar white powder does not react with vinegar

Rubbing alcohol clear liquid flammable

Red food coloring red color reacts with bleach andloses color

Iron malleable reacts with oxygen

Comparing Physical and Chemical Properties


Changing Change

1. Place a folded papertowel in a small pieplate.

2. Pour vinegar intothe pie plate untilthe entire papertowel is damp.

3. Place two or three shinypennies on top of thepaper towel.

4. Put the pie plate in a placewhere it won’t be both-ered, and wait 24 hours.

5. Describe the chemicalchange that took place.

6. Write your observations inyour ScienceLog.

Examples of Physical Changes Melting isa good example of a physical change, as youcan see in Figure 15. Still another physicalchange occurs when a substance dissolvesinto another substance. If you dissolvesugar in water, the sugar seems todisappear into the water. But theidentity of the sugar does notchange. If you taste thewater, you will also stilltaste the sugar. The sugarhas undergone a physicalchange. See the chart be-low for more examples ofphysical changes.

Can Physical Changes Be Undone? Because physicalchanges do not change the identity of substances, they areoften easy to undo. If you leave butter out on a warm counter,it will undergo a physical change—it will melt. Putting it backin the refrigerator will reverse this change. Likewise, if you cre-ate a figure from a lump of clay, you change the clay’s shape,causing a physical change. But because the identity of the claydoes not change, you can crush your creation and form theclay back into its previous shape.

Chemical Changes Form New SubstancesA chemical change occurs when one or more substances arechanged into entirely new substances with different proper-ties. Chemical changes will or will not occur as described bythe chemical properties of substances. But chemical changesand chemical properties are not the same thing. A chemicalproperty describes a substance’s ability to go through a chemi-cal change; a chemical change is the actual process in whichthat substance changes into another substance. You can observechemical properties only when a chemical change might occur.


Freezing water for ice cubes

Sanding a piece of wood

Cutting your hair

Crushing an aluminum can

Bending a paper clip

Mixing oil and vinegar

Figure 15 A physicalchange turned a stick ofbutter into the liquid butterthat makes popcorn sotasty, but the identity ofthe butter did not change.

More Examples of Physical Changes

Examples of Chemical Changes

A fun (and delicious) way to see what happens during chemi-cal changes is to bake a cake. When you bakea cake, you combine eggs, flour, sugar, but-ter, and other ingredients as shown inFigure 16. Each ingredient has its own setof properties. But if you mix themtogether and bake the batter in theoven, you get something com-pletely different. The heat ofthe oven and the interactionof the ingredients cause achemical change. As shownin Figure 17, you get a cakethat has properties com-pletely different to any of theingredients. Some more exam-ples of chemical changes areshown below.

Figure 16 Each of these ingredi-ents has different physical andchemical properties.

The hot gas formed whenhydrogen and oxygen join tomake water helps blast thespace shuttle into orbit.

The Statue of Liberty is made of shiny, orange-brown copper.But the metal’s interaction withcarbon dioxide and water hasformed a new substance, coppercarbonate, and made this land-mark lady green over time.

Chapter 250

Figure 17 Chemical changes produce newsubstances with different properties.

Soured milk smells badbecause bacteria haveformed new substancesin the milk.

Effervescent tablets bubblewhen the citric acid and bakingsoda in them react with water.



Clues to Chemical Changes Look back at the bottom ofthe previous page. In each picture, there is at least one cluethat signals a chemical change. Can you find the clues? Here’sa hint: chemical changes often cause color changes, fizzing orfoaming, heat, or the production of sound, light, or odor.

In the cake example, you would probably smell the sweetaroma of the cake as it baked. If you looked into the oven,you would see the batter rise and turn brown. When you cutthe finished cake, you would see the spongy texture createdby gas bubbles that formed in the batter (if you baked it right,that is!). All of these yummy clues are signals of chemicalchanges. But are the clues and the chemical changes the samething? No, the clues just result from the chemical changes.

Can Chemical Changes Be Undone? Because new sub-stances are formed, you cannot reverse chemical changes usingphysical means. In other words, you can’t uncrumple or ironout a chemical change. Imagine trying to un-bake the cakeshown in Figure 18 by pulling out each ingredient.No way! Most of the chemical changes yousee in your daily life, such as a cake bak-ing or milk turning sour, would be dif-ficult to reverse. However, somechemical changes can be reversedunder the right conditions byother chemical changes. Forexample, the water formed inthe space shuttle’s rocketscould be split back intohydrogen and oxygenusing an electric current.

1. Classify each of the following properties as either physi-cal or chemical: reacts with water, dissolves in acetone,is blue, does not react with hydrogen.

2. List three clues that indicate a chemical change might betaking place.

3. Comparing Concepts Describe the difference betweenphysical changes and chemical changes in terms of whathappens to the matter involved in each kind of change.


REVIEW


When fossil fuels are burned, achemical change takes place involv-ing sulfur (a substance in fossil fuels)and oxygen (from the air). Thischemical change produces sulfurdioxide, a gas. When sulfur dioxideenters the atmosphere, it undergoesanother chemical change by interact-ing with water and oxygen. Thischemical change produces sulfuricacid, a contributor to acid precipita-tion. Acid precipitation can kill treesand make ponds and lakes unable tosupport life.

Figure 18 Looking forthe original ingredi-

ents? You won’t findthem—their identitieshave changed.

NSTA

TOPIC: Describing MatterGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP035

Chapter Highlights

Chapter 252

SECTION 1

Vocabularymatter (p. 36)

volume (p. 36)

meniscus (p. 37)

mass (p. 38)

gravity (p. 39)

weight (p. 40)

newton (p. 41)

inertia (p. 42)

Section Notes

• Matter is anything that hasvolume and mass.

• Volume is the amount ofspace taken up by an object.

• The volume of liquids isexpressed in liters and milliliters.

• The volume of solid objectsis expressed in cubic units,such as cubic meters.

• Mass is the amount of matterthat something is made of.

• Mass and weight are not thesame thing. Weight is a meas-ure of the gravitational forceexerted on an object, usuallyin relation to the Earth.

• Mass is usually expressed inmilligrams, grams, and kilograms.

• The newton is the SI unit offorce, so weight is expressedin newtons.

• Inertia is the tendency of allobjects to resist any changein motion. Mass is a measureof inertia. The more massivean object is, the greater itsinertia.

LabsVolumania! (p. 630)

Skills CheckMath ConceptsDENSITY To calculate an object’s density,divide the mass of the object by its volume. Forexample, the density of an object with a massof 45 g and a volume of 5.5 cm3 is calculated asfollows:

D mV

D 5.455cmg

3

D 8.2 g/cm3

Visual UnderstandingMASS AND WEIGHTMass and weight arerelated, but they’re not thesame thing. Look back atFigure 8 on page 41 tolearn about the differencesbetween mass and weight.

PHYSICAL AND CHEMICAL PROPERTIES Allsubstances have physical and chemical proper-ties. You can compare some of those propertiesby reviewing the table on page 48.



TOPIC: What Is Matter? sciLINKS NUMBER: HSTP030

TOPIC: Describing Matter sciLINKS NUMBER: HSTP035

TOPIC: Dark Matter sciLINKS NUMBER: HSTP040

TOPIC: Building a Better Body sciLINKS NUMBER: HSTP045



KEYWORD: HSTMAT

53The Properties of Matter

SECTION 2

Vocabularyphysical property (p. 43)

density (p. 44)

chemical property (p. 47)

physical change (p. 48)

chemical change (p. 49)

Section Notes

• Physical properties of mattercan be observed withoutchanging the identity of thematter.

• Density is the amount ofmatter in a given space, orthe mass per unit volume.

• The density of a substance isalways the same at a givenpressure and temperatureregardless of the size of thesample of the substance.

• Chemical properties describea substance based on itsability to change into a newsubstance with differentproperties.

• Chemical properties can beobserved only when one sub-stance might become a newsubstance.

• The characteristic propertiesof a substance are always thesame whether the sampleobserved is large or small.

• When a substance undergoesa physical change, its iden-tity remains the same.

• A chemical change occurswhen one or more sub-stances are changed into new substances with dif-ferent properties.

LabsDetermining Density (p. 632)

Layering Liquids (p. 633)

White Before Your Eyes (p. 634)




1. mass/volume

2. mass/weight

3. inertia/mass

4. volume/density

5. physical property/chemical property

6. physical change/chemical change


Multiple Choice

7. Which of these is not matter?a. a cloud c. sunshineb. your hair d. the sun

8. The mass of an elephant on the moonwould be a. less than its mass on Mars. b. more than its mass on Mars.c. the same as its weight on the moon.d. None of the above

9. Which of the following is not a chemicalproperty?a. reactivity with oxygenb. malleabilityc. flammabilityd. reactivity with acid

10. Your weight could beexpressed in which of thefollowing units?a. poundsb. newtonsc. kilogramsd. both (a) and (b)

11. You accidentally break your pencil in half.This is an example ofa. a physical change.b. a chemical change.c. density.d. volume.

12. Which of the following statements aboutdensity is true?a. Density depends on mass and volume.b. Density is weight per unit volume.c. Density is measured in milliliters.d. Density is a chemical property.

13. Which of the following pairs of objectswould have the greatest attraction towardeach other due to gravity?a. a 10 kg object and a 10 kg object,

4 m apart b. a 5 kg object and a 5 kg object,

4 m apart c. a 10 kg object and a 10 kg object,

2 m apartd. a 5 kg object and a 5 kg object,

2 m apart

14. Inertia increases as ? increases. a. time c. massb. length d. volume

Short Answer

15. In one or two sentences, explain the dif-ferent processes in measuring the volumeof a liquid and measuring the volume of a solid.

16. In one or two sentences,explain the relationshipbetween mass and inertia.

17. What is the formula forcalculating density?

18. List three characteristicproperties of matter.

54 Chapter 2Copyright © by Holt, Rinehart and Winston. All rights reserved.

Concept Mapping

19. Use the followingterms to create aconcept map: matter,mass, inertia, vol-ume, milliliters,cubic centimeters,weight, gravity.


20. You are making breakfast for your pickyfriend, Filbert. You make him scrambledeggs. He asks, “Would you please takethese eggs back to the kitchen and poachthem?” What scientific reason do yougive Filbert for not changing his eggs?

21. You look out your bedroom window andsee your new neighbors moving in. Yourneighbor bends over to pick up a smallcardboard box, but he cannot lift it. Whatcan you conclude about the item(s) in thebox? Use the terms mass and inertia toexplain how you came to this conclusion.

22. You may sometimes hear on the radio oron television that astronauts are “weight-less” in space. Explain why this is nottrue.

23. People commonly use the term volume todescribe the capacity of a container. Howdoes this definition of volume differ fromthe scientific definition?

MATH IN SCIENCE

24. What is the volume of a book with thefollowing dimensions: a width of 10 cm, alength that is two times the width, and aheight that is half the width? Rememberto express your answer in cubic units.

25. A jar contains 30 mL of glycerin (mass =37.8 g) and 60 mL of corn syrup (mass =82.8 g). Which liquid is on top? Showyour work, and explain your answer.


Examine the photograph below, and answerthe following questions:

26. List three physical properties of this can.

27. Did a chemical change or a physicalchange cause the change in this can’sappearance?

28. How does the density of the metal in thecan compare before and after the change?

29. Can you tell what the chemical propertiesof the can are just by looking at the pic-ture? Explain.


Poach these,please!



ReadingCheck-up


P H Y S I C A L S C I E N C E • A S T R O N O M Y

In the Dark About Dark Matter

56

What is the universe made of?Believe it or not, whenastronomers try to answer thisquestion, they still find them-selves in the dark. Surprisingly,there is more to the universethan meets the eye.

A Matter of GravityAstronomers noticed some-thing odd when studying themotions of galaxies in space.They expected to find a lot ofmass in the galaxies. Instead,they discovered that the massof the galaxies was not greatenough to explain the large gravitational forcecausing the galaxies’ rapid rotation. So whatwas causing the additional gravitational force?Some scientists think the universe containsmatter that we cannot see with our eyes or ourtelescopes. Astronomers call this invisible mat-ter dark matter.

Dark matter doesn’t reveal itself by givingoff any kind of electromagnetic radiation, suchas visible light, radio waves, or gamma radia-tion. According to scientific calculations, darkmatter could account for between 90 and 99percent of the total mass of the universe! Whatis dark matter? Would you believe MACHOs and WIMPs?

MACHOsScientists recently proved the existence ofMAssive Compact Halo Objects (MACHOs) inour Milky Way galaxy by measuring their gravi-tational effects. Even though scientists knowMACHOs exist, they aren’t sure what MACHOsare made of. Scientists suggest that MACHOsmay be brown dwarfs, old white dwarfs, neu-tron stars, or black holes. Others suggest they

are some type of strange, newobject whose properties stillremain unknown. Even thoughthe number of MACHOs isapparently very great, they stilldo not represent enough miss-ing mass. So scientists offeranother candidate for darkmatter—WIMPs.

WIMPsTheories predict that WeaklyInteracting Massive Particles(WIMPs) exist, but scientistshave never detected them.WIMPs are thought to be mas-

sive elementary particles that do not interactstrongly with normal matter (which is why scientists have not found them).

More Answers NeededSo far, evidence supports the existence ofMACHOs, but there is little or no solid evidenceof WIMPs or any other form of dark matter.Scientists who support the idea of WIMPs areconducting studies of the particles that makeup matter to see if they can detect WIMPs.Other theories are that gravity acts differentlyaround galaxies or that the universe is filledwith things called “cosmic strings.” Scientistsadmit they have a lot of work to do before theywill be able to describe the universe—and allthe matter in it.

On Your Own What is microlensing, and what does it haveto do with MACHOs? How might the neutrinoprovide valuable information to scientists whoare interested in proving the existence ofWIMPs? Find out on your own!

The Large MagellanicCloud, located 180,000light-years from Earth


57

Have you ever broken anarm or a leg? If so, youprobably wore a cast

while the bone healed. Butwhat happens when a bone istoo badly damaged to heal? Insome cases, a false bone madefrom a metal called titaniumcan take the original bone’splace. Could using titaniumbone implants be the first stepin creating bionic body parts?Think about it as you readabout some of titanium’samazing properties.

Imitating the OriginalWhy would a metal like titanium be used toimitate natural bone? Well, it turns out that atitanium implant passes some key tests forbone replacement. First of all, real bones areincredibly lightweight and sturdy, and healthybones last for many years. Therefore, a bone-replacement material has to be lightweight butalso very durable. Titanium passes this testbecause it is well known for its strength, and it is also lightweight.

Second, the human body’s immune systemis always on the lookout for foreign substances.If a doctor puts a false bone in place and thepatient’s immune system attacks it, an infectioncan result. Somehow, the false bone must beable to chemically trick the body into thinkingthat the bone is real. Does titanium pass thistest? Keep reading!

Accepting ImitationBy studying the human body’s immune system,scientists found that the body accepts certainmetals. The body almost always accepts onemetal in particular. Yep, you guessed it—tita-nium! This turned out to be quite a discovery.

Doctors could implant pieces oftitanium into a person’s bodywithout triggering an immunereaction. A bond can even formbetween titanium and existingbone tissue, fusing the bone tothe metal!

Titanium is shaping up tobe a great bone-replacementmaterial. It is lightweight andstrong, is accepted by the body,can attach to existing bone,and resists chemical changes,such as corrosion. But scientistshave encountered a slight prob-lem. Friction can wear away

titanium bones, especially those used near thehips and elbows.

Real SuccessAn unexpected surprise, not from the field ofmedicine but from the field of nuclear physics,may have solved the problem. Researchershave learned that by implanting a special formof nitrogen on the surface of a piece ofmetal, they can create a surface layer onthe metal that is especially durable andwear-resistant. When this form of nitrogenis implanted in titanium bones, the bonesretain all the properties of pure titaniumbones but also become very wear-resistant.The new bones should last through decadesof heavy use without needing to be replaced.

Think About It What will the future hold? As time goes by, doctors become more successful atimplanting titanium bones. What do youthink would happen if the titanium boneswere to eventually become better than real bones?

Building a Better Body

Titanium bones—evenbetter than the real thing?


58 Chapter 3

Four States of Matter . . 60Internet Connect . . . . . 64MathBreak . . . . . . . . . . 66Apply . . . . . . . . . . . . . . 67Internet Connect. . . . . . 67

Changes of State . . . . . 68QuickLab . . . . . . . . . . . 71Meteorology

Connection . . . . . . . . 71Internet Connect . . . . . 73

Chapter Review . . . . . . . . . . 76

Feature Articles. . . . . . . . 78, 79

LabBook . . . . . . . . . . . 636–639

States ofMatterStates ofMatter

It Takes Mettle to Melt MetalIf you wanted to make a flavored ice pop, you would pourjuice into a mold and freeze it. You are able to make the ice pop into the desired shape because, unlike solids, liquids will take the shape of their container. Metal workersapply this important property of liquids when they createmetal parts that have complicated shapes. They melt themetal at extremely high temperatures and then pour it into a mold. In this chapter, you will find out more aboutthe properties of different states of matter.


1. What are the four mostfamiliar states of matter?

2. Compare the motion ofparticles in a solid, a liquid, and a gas.

3. Name three ways matterchanges from one stateto another.


59

VANISHING ACTIn this activity, you will use rubbingalcohol to investigate a change ofstate.

Procedure

1. Pour rubbing alcohol into a small plastic cup until the alcohol just covers the bottomof the cup.

2. Moisten the tip of a cotton swabby dipping it into the alcohol inthe cup.

3. Rub the cotton swab on the palmof your hand.

4. Record your observations in yourScienceLog.

5. Wash your hands thoroughly.

Analysis

6. Explain what happened to thealcohol.

7. Did you feel a sensation of hot orcold? If so, how do you explainwhat you observed?

8. Record your answers in yourScienceLog.

States of MatterCopyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 360

Four States of MatterFigure 1 shows a model of theearliest known steam engine,invented about A.D. 60 byHero, a scientist who lived inAlexandria, Egypt. This modelalso demonstrates the fourmost familiar states of matter:solid, liquid, gas, and plasma.The states of matter are thephysical forms in which a sub-stance can exist. For example,water commonly exists inthree different states of mat-ter: solid (ice), liquid (water),and gas (steam).

Moving Particles Make Up All MatterMatter consists of tiny particles called atoms and molecules(MAHL i KYOOLZ) that are too small to see without an amazinglypowerful microscope. These atoms and molecules are always inmotion and are constantly bumping into one another. The stateof matter of a substance is determined by how fast the particlesmove and how strongly the particles are attracted to one another.Figure 2 illustrates three of the states of matter—solid, liquid,and gas—in terms of the speed and attraction of the particles.

Figure 1 This model of Hero’ssteam engine spins as steamescapes through the nozzles.

Particles of a solid do not movefast enough to overcome thestrong attraction between them,so they are held tightly in place.The particles vibrate in place.


Particles of a gas move fastenough to overcome nearlyall of the attraction betweenthem. The particles moveindependently of one another.


Gas

Solid

Liquid

Plasma

Section

1

states of matter pressuresolid Boyle’s lawliquid Charles’s lawgas plasma

Describe the properties sharedby particles of all matter.

Describe the four states of mat-ter discussed here.

Describe the differencesbetween the states of matter.

Predict how a change in pres-sure or temperature will affectthe volume of a gas.



Figure 4 Differing arrangements of particles in crys-talline solids and amorphous solids lead to differentproperties. Imagine trying to hit a home run with arubber bat!

Solids Have Definite Shape and VolumeLook at the ship in Figure 3. Even in a bottle, it keepsits original shape and volume. If you moved theship to a larger bottle, the ship’s shape and vol-ume would not change. Scientifically, the statein which matter has a definite shape and vol-ume is solid. The particles of a substance in asolid are very close together. The attractionbetween them is stronger than the attractionbetween the particles of the same substance inthe liquid or gaseous state. The atoms or mol-ecules in a solid move, but not fast enough toovercome the attraction between them. Each parti-cle vibrates in place because it is locked in positionby the particles around it.

Two Types of Solids Solids are often divided into two cat-egories—crystalline and amorphous (uh MOHR fuhs). Crystallinesolids have a very orderly, three-dimensional arrangement ofatoms or molecules. That is, the particles are arranged in arepeating pattern of rows. Examples of crystalline solids includeiron, diamond, and ice. Amorphous solids are composed ofatoms or molecules that are in no particular order. That is, eachparticle is in a particular spot, but the particles are in no organ-ized pattern. Examples of amorphous solids include rubber andwax. Figure 4 illustrates the differences in the arrangement ofparticles in these two solids.

States of Matter 61

The particles in anamorphous soliddo not have anorderly arrangement.

The particles in acrystalline solidhave a very orderlyarrangement.

Figure 3 Because this ship is asolid, it does not take the shapeof the bottle.

Imagine that you are a parti-cle in a solid. Your position inthe solid is your chair. In yourScienceLog, describe the dif-ferent types of motion thatare possible even though youcannot leave your chair.


Liquids Change Shape but Not VolumeA liquid will take the shape of whatever container it is put in.You are reminded of this every time you pour yourself a glassof juice. The state in which matter takes the shape of its con-

tainer and has a definite volume is liquid. The atoms ormolecules in liquids move fast enough to overcome

some of the attractions between them. The parti-cles slide past each other until the liquid takesthe shape of its container. Figure 5 shows howthe particles in juice might look if they werelarge enough to see.

Even though liquids change shape, they donot readily change volume. You know that acan of soda contains a certain volume of liquidregardless of whether you pour it into a largecontainer or a small one. Figure 6 illustrates thispoint using a beaker and a graduated cylinder.

Chapter 362

The Boeing 767 Freighter, atype of commercial airliner,has 187 km (116 mi) ofhydraulic tubing.

Figure 6 Even when liquidschange shape, they don’t changevolume.

The Squeeze Is On Because the particles in liquids are closeto one another, it is difficult to push them closer together. Thismakes liquids ideal for use in hydraulic (hie DRAW lik) sys-tems. For example, brake fluid is the liquid used in the brakesystems of cars. Stepping on the brake pedal applies a force tothe liquid. The particles in the liquid move away rather thansqueezing closer together. As a result, the fluid pushes the brakepads outward against the wheels, which slows the car.

Figure 5 Particles in a liquidslide past one another untilthe liquid conforms to theshape of its container.


A Drop in the Bucket Two other important properties ofliquids are surface tension and viscosity (vis KAHS uh tee). Surfacetension is the force acting on the particles at the surface of a liquid that causes the liquid to form spherical drops, as shown in Figure 7. Different liquids have different surfacetensions. For example, rubbing alcohol has a lower surface tension than water, but mercury has a higher surface tensionthan water.

Viscosity is a liquid’s resistance to flow. In general, thestronger the attractions between a liquid’s particles are, themore viscous the liquid is. Think of the difference betweenpouring honey and pouring water. Honey flows more slowlythan water because it has a higher viscosity than water.

Gases Change Both Shape and VolumeHow many balloons can be filled from a single metal cylin-der of helium? The number may surprise you. One cylindercan fill approximately 700 balloons. How is this possible?After all, the volume of the metal cylinder is equal to thevolume of only about five inflated balloons.

It’s a Gas! Helium is a gas. Gas is thestate in which matter changes in bothshape and volume. The atoms or mol-ecules in a gas move fast enough tobreak away completely from oneanother. Therefore, the particles of asubstance in the gaseous state have lessattraction between them than particlesof the same substance in the solid orliquid state. In a gas, there is emptyspace between particles.

The amount of empty space in a gascan change. For example, the heliumin the metal cylinder consists of atomsthat have been forced very closetogether, as shown in Figure 8. As thehelium fills the balloon, the atomsspread out, and the amount of emptyspace in the gas increases. As you con-tinue reading, you will learn how thisempty space is related to pressure.

63

Figure 7 Liquids formspherical drops as a resultof surface tension.

Figure 8 The particles of the gas in thecylinder are much closer together thanthe particles of the gas in the balloons.


Gas Under PressurePressure is the amount of force exerted on a given area. Youcan think of this as the number of collisions of particles againstthe inside of the container. Compare the basketball with thebeach ball in Figure 9. The balls have the same volume andcontain particles of gas (air) that constantly collide with oneanother and with the inside surface of the balls. Notice, how-ever, that there are more particles in the basketball than inthe beach ball. As a result, more particles collide with theinside surface of the basketball than with the inside surface ofthe beach ball. When the number of collisions increases, theforce on the inside surface of the ball increases. This increasedforce leads to increased pressure.

Chapter 364

Figure 9 Both balls shown here are full of air, but the pressure inthe basketball is higher than the pressure in the beach ball.

1. List two properties that all particles of matter have incommon.

2. Describe solids, liquids, and gases in terms of shape andvolume.

3. Why can the volume of a gas change?

4. Applying Concepts Explain what happens inside the ballwhen you pump up a flat basketball.

The beach ball has a lower pressurethan the basketball because the lessernumber of particles of gas are fartherapart. Therefore, they collide with theinside of the ball at a slower rate.

The basketball has a higher pressurethan the beach ball because the greaternumber of particles of gas are closertogether. Therefore, they collide withthe inside of the ball at a faster rate.

REVIEW

Self-CheckHow would an increasein the speed of theparticles affect thepressure of gas in ametal cylinder? (Seepage 724 to check youranswer.)

NSTA

TOPIC: Solids, Liquids, and GasesGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP060


Laws Describe Gas BehaviorEarlier in this chapter, you learned about the atoms and mol-ecules in both solids and liquids. You learned that comparedwith gas particles, the particles of solids and liquids are closelypacked together. As a result, solids and liquids do not changevolume very much. Gases, on the other hand, behave differ-ently; their volume can change by a large amount.

It is easy to measure the volume of a solid or liquid, buthow do you measure the volume of a gas? Isn’t the volume ofa gas the same as the volume of its container? The answer isyes, but there are other factors, such as pressure, to consider.

Boyle’s Law Imagine a diver at a depth of 10 m blowing abubble of air. As the bubble rises, its volume increases. By thetime the bubble reaches the surface, its original volume willhave doubled due to the decrease in pressure. The relation-ship between the volume and pressure of a gas is known asBoyle’s law because it was first described by Robert Boyle, aseventeenth-century Irish chemist. Boyle’s law states that fora fixed amount of gas at a constant temperature, the volumeof a gas increases as its pressure decreases. Likewise, the vol-ume of a gas decreases as its pressure increases. Boyle’s law isillustrated by the model in Figure 10.

States of Matter 65

Releasing the plunger allowsthe gas to change to an inter-mediate volume and pressure.

Pushing the plunger increasesthe pressure of the gas. Theparticles of gas are forcedcloser together. The volume of the gas decreases as thepressure increases.

Lifting the plunger decreasesthe pressure of the gas. Theparticles of gas spread fartherapart. The volume of the gasincreases as the pressuredecreases.

Figure 10 Boyle’s LawEach illustration shows the same piston and thesame amount of gas at the same temperature.


Weather balloons demonstrate a practical use of Boyle’slaw. A weather balloon carries equipment into the atmosphereto collect information used to predict the weather. This balloonis filled with only a small amount of gas because the pressureof the gas decreases and the volume increases as the balloonrises. If the balloon were filled with too much gas, it wouldpop as the volume of the gas increased.

Charles’s Law An inflated balloon will also pop when it getstoo hot, demonstrating another gas law—Charles’s law.Charles’s law states that for a fixed amount of gas at a con-stant pressure, the volume of the gas increases as its tempera-ture increases. Likewise, the volume of the gas decreases as itstemperature decreases. Charles’s law is illustrated by the modelin Figure 11. You can see Charles’s law in action by puttingan inflated balloon in the freezer. Wait about 10 minutes, andsee what happens!

Chapter 366

Gas Law GraphsEach graph below illustratesa gas law. However, the vari-able on one axis of eachgraph is not labeled. Answerthe following questions foreach graph:

1. As the volume increases,what happens to the miss-ing variable?

2. Which gas law is shown?

3. What label belongs on theaxis?

4. Is the graph linear or non-linear? What does this tellyou?

MATH BREAK

Graph A

Graph B

?

Volu

me

?

Volu

me

See Charles’s law in action foryourself using a balloon

on page 636 of theLabBook.

Lowering the temperature of the gas causes the particles to movemore slowly. They hit the sides of the piston less often and with lessforce. As a result, the volume of the gas decreases.

Raising the temperature of the gas causes the particles to movemore quickly. They hit the sides of the piston more often and withgreater force. As a result, the volumeof the gas increases.

Figure 11 Charles’s LawEach illustration shows the same piston and thesame amount of gas at the same pressure.


PlasmasScientists estimate that more than 99 percent of the knownmatter in the universe, including the sun and other stars, ismade of a state of matter called plasma. Plasma is the state ofmatter that does not have a definite shape or volume andwhose particles have broken apart.

Plasmas have some properties that are quite different fromthe properties of gases. Plasmas conduct electric current, whilegases do not. Electric and magnetic fields affect plasmas butdo not affect gases. In fact, strongmagnetic fields are used to con-tain very hot plasmas that woulddestroy any other container.

Natural plasmas are found inlightning, fire, and the incrediblelight show in Figure 12, called theaurora borealis (ah ROHR uh BOHR

ee AL is). Artificial plasmas, foundin fluorescent lights and plasmaballs, are created by passing elec-tric charges through gases.

States of Matter 67

1. When scientists record the volume of a gas, why do theyalso record the temperature and the pressure?

2. List two differences between gases and plasmas.

3. Applying Concepts What happens to the volume of aballoon left on a sunny windowsill? Explain.

Figure 12 Auroras, like theaurora borealis seen here, formwhen high-energy plasma col-lides with gas particles in theupper atmosphere.

Charles’s Law and Bicycle Tires

One of your friends overinflated thetires on her bicycle. Use Charles’s law to explain why she should let out some of the air before going for a ride on a hot day.

REVIEW

NSTA

TOPIC: Natural and Artificial PlasmaGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP065

Chapter 3

Changes of StateA change of state is the conversion of a substance from onephysical form to another. All changes of state are physicalchanges. In a physical change, the identity of a substance doesnot change. In Figure 13, the ice, liquid water, and steam areall the same substance—water. In this section, you will learnabout the four changes of state illustrated in Figure 13 as wellas a fifth change of state called sublimation (SUHB li MAY shuhn).

Energy and Changes of StateDuring a change of state, the energy of a substance changes.The energy of a substance is related to the motion of its par-ticles. The molecules in the liquid water in Figure 13 movefaster than the molecules in the ice. Therefore, the liquid waterhas more energy than the ice.

If energy is added to a substance, its particles move faster.If energy is removed, its particles move slower. The tempera-ture of a substance is a measure of the speed of its particlesand therefore is a measure of its energy. For example, steamhas a higher temperature than liquid water, so particles insteam have more energy than particles in liquid water. A trans-fer of energy, known as heat, causes the temperature of a sub-stance to change, which can lead to a change of state.

Freezing

Vapo

riza

tion

Melting

Cond

ensa

tio

n

Figure 13 The terms in the arrows arechanges of state. Water commonly goesthrough the changes of state shown here.

Want to learn how to get

power fromchanges ofstate? Steam

ahead topage 79.

68

Section

2

change of state boilingmelting evaporationfreezing condensationvaporization sublimation

Describe how substances changefrom state to state.

Explain the difference betweenan exothermic change and anendothermic change.

Compare the changes of state.



Melting: Solids to LiquidsMelting is the change of state from a solid to a liquid. This iswhat happens when an ice cube melts. Figure 14 shows a metalcalled gallium melting. What is unusual about this metal isthat it melts at around 30°C. Because your normal body tem-perature is about 37°C, gallium will melt right in your hand!

The melting point of a substance is the temperature at whichthe substance changes from a solid to a liquid. Melting pointsof substances vary widely. The melting point of gallium is 30°C. Common table salt, however, has a melting point of 801°C.

Most substances have a unique melting point that can beused with other data to identify them. Because the meltingpoint does not change with different amounts of the sub-stance, melting point is a characteristic property of a substance.

Absorbing Energy For a solid to melt, particles must over-come some of their attractions to each other. When a solid isat its melting point, any energy it absorbs increases the motionof its atoms or molecules until they overcome the attractionsthat hold them in place. Melting is an endothermic changebecause energy is absorbed by the substance as it changes state.

Freezing: Liquids to SolidsFreezing is the change of state from a liquid to a solid. Thetemperature at which a liquid changes into a solid is its freez-ing point. Freezing is the reverse process of melting, so freez-ing and melting occur at the sametemperature, as shown in Figure 15.

Removing Energy For a liquid tofreeze, the motion of its atoms ormolecules must slow to the pointwhere attractions between them over-come their motion. If a liquid is atits freezing point, removing moreenergy causes the particles to beginlocking into place. Freezing is anexothermic change because energy isremoved from, or taken out of, thesubstance as it changes state.

States of Matter 69

Figure 14 Even though galliumis a metal, it would not be veryuseful as jewelry!

Figure 15 Liquid waterfreezes at the sametemperature that icemelts—0°C.

If energy is added at0°C, the ice will melt.

If energy is removedat 0°C, the liquidwater will freeze.


Vaporization: Liquids to GasesOne way to experience vaporization (VAY puhr i ZAY shuhn) isto iron a shirt—carefully!—using a steam iron. You will noticesteam coming up from the iron as the wrinkles are eliminated.

This steam results from the vaporization of liquid water bythe iron. Vaporization is simply the change of state froma liquid to a gas.

Boiling is vaporization that occurs throughout a liquid.The temperature at which a liquid boils is called its boilingpoint. Like the melting point, the boiling point is a char-acteristic property of a substance. The boiling point of wateris 100°C, whereas the boiling point of liquid mercury is357°C. Figure 16 illustrates the process of boiling and a sec-

ond form of vaporization—evaporation (ee VAP uh RAY shuhn).Evaporation is vaporization that occurs at the surface of a

liquid below its boiling point, as shown in Figure 16. Whenyou perspire, your body is cooled through the process of evapo-ration. Perspiration is mostly water. Water absorbs energy fromyour skin as it evaporates. You feel cooler because your bodytransfers energy to the water. Evaporation also explains whywater in a glass on a table disappears after several days.

Chapter 370

Figure 16 Both boilingand evaporation changea liquid to a gas.

Self-CheckIs vaporization anendothermic orexothermic change?(See page 724 to checkyour answer.)

Boilingpoint

Boilingpoint

Boiling occurs in a liquid at its boiling point.As energy is added to the liquid, particlesthroughout the liquid move fast enough tobreak away from the particles around themand become a gas.

Evaporation occurs in a liquid belowits boiling point. Some particles at thesurface of the liquid move fast enoughto break away from the particlesaround them and become a gas.


Boiling Water Is Cool

1. Remove the capfrom a syringe.

2. Place the tip of thesyringe in the warmwater provided byyour teacher. Pull theplunger out until you have10 mL of water in thesyringe.

3. Tightly cap the syringe.

4. Hold the syringe, andslowly pull the plunger out.

5. Observe any changes yousee in the water. Recordyour observations in yourScienceLog.

6. Why are you not burned bythe boiling water in thesyringe?

Pressure Affects Boiling Point Earlier you learned that waterboils at 100C. In fact, water only boils at 100C at sea levelbecause of atmospheric pressure. Atmospheric pressure is causedby the weight of the gases that make up the atmosphere.Atmospheric pressure varies depending on where you are inrelation to sea level. Atmospheric pressure is lower at higherelevations. The higher you go above sea level, the less air thereis above you, and the lower the atmospheric pressure is. If youwere to boil water at the top of a mountain, the boiling pointwould be lower than 100C. For example, Denver, Colorado, is1.6 km (1 mi) above sea level and water boils there at about95C. You can make water boil at an even lower temperatureby doing the QuickLab at right.

Condensation: Gases to LiquidsLook at the cool glass of lemonade in Figure 17. Notice thebeads of water on the outside of the glass. These form asa result of condensation. Condensation is the change ofstate from a gas to a liquid. The condensation point of asubstance is the temperature at which the gas becomes aliquid and is the same temperature as the boiling point ata given pressure. Thus, at sea level, steam condenses to form water at 100C—the same temperature at which water boils.

For a gas to become a liquid,large numbers of atoms or mol-ecules must clump together.Particles clump together whenthe attraction between themovercomes their motion. For thisto occur, energy must be re-moved from the gas to slow the particles down. Therefore,condensation is an exothermicchange.

71States of Matter


The amount of gaseous water thatair can hold decreases as the tem-perature of the air decreases. As theair cools, some of the gaseous watercondenses to form small drops ofliquid water. These drops formclouds in the sky and fog near theground.

Figure 17 Gaseous water inthe air will become liquid whenit contacts a cool surface.


Sublimation: Solids Directly to GasesLook at the solids shown in Figure 18. The solid on the left isice. Notice the drops of liquid collecting as it melts. On theright, you see carbon dioxide in the solid state, also called dryice. It is called dry ice because instead of melting into a liquid,

it goes through a change of state called subli-mation. Sublimation is the change of state froma solid directly into a gas. Dry ice is colder thanice, and it doesn't melt into a puddle of liquid.It is often used to keep food, medicine, andother materials cold without getting them wet.

For a solid to change directly into a gas, theatoms or molecules must move from being verytightly packed to being very spread apart. Theattractions between the particles must be com-pletely overcome. Because this requires the addi-tion of energy, sublimation is an endothermicchange.

Comparing Changes of StateAs you learned in Section 1 of this chapter, thestate of a substance depends on how fast its atomsor molecules move and how strongly they areattracted to each other. A substance may undergoa physical change from one state to another byan endothermic change (if energy is added) oran exothermic change (if energy is removed).The table below shows the differences betweenthe changes of state discussed in this section.

Chapter 372

Summarizing the Changes of State

Ice melts into liquid water at 0C.

Liquid water freezes into ice at 0C.

Liquid water vaporizes into steamat 100°C.

Steam condenses into liquid water at 100C.

Solid dry ice sublimes into a gas at –78C.

Melting solid liquid endothermic

Freezing liquid solid exothermic

Vaporization liquid gas endothermic

Condensation gas liquid exothermic

Sublimation solid gas endothermic

Change of state Direction Example

Figure 18 Ice melts, but dry ice, on the right,turns directly into a gas.

Endothermic or exothermic?


Temperature Change Versus Change of StateWhen most substances lose or absorb energy, one of two thingshappens to the substance: its temperature changes or its statechanges. Earlier in the chapter, you learned that the temper-ature of a substance is a measure of the speed of the particles.This means that when the temperature of a substance changes,the speed of the particles also changes. But while a substancechanges state, its temperature does not change until the changeof state is complete, as shown in Figure 19.

States of Matter 73

Boiling point

Melting point

Time

Tem

pera

ture

( C

)

100

0

o

ENER

GY

ADDED ENER

GY ADDED

ENER

GY ADDED ENERGY

ADD

ED

1. Compare endothermic and exothermic changes.

2. Classify each change of state (melting, freezing, vapor-ization, condensation, and sublimation) as endothermicor exothermic.

3. Describe how the motion and arrangement of particleschange as a substance freezes.

4. Comparing Concepts How are evaporation and boilingdifferent? How are they similar?

REVIEW

Figure 19 Changing the State of Water

Temperature remains atthe melting point until allof the solid has melted.

Temperature remains atthe boiling point until allof the liquid has boiled.

NSTA

TOPIC: Changes of StateGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP070

Chapter Highlights

Chapter 374

SECTION 1

Vocabularystates of matter (p. 60)

solid (p. 61)

liquid (p. 62)

gas (p. 63)

pressure (p. 64)

Boyle’s law (p. 65)

Charles’s law (p. 66)

plasma (p. 67)

Section Notes

• The states of matter are thephysical forms in which asubstance can exist. The fourmost familiar states are solid,liquid, gas, and plasma.

• All matter is made of tinyparticles called atoms andmolecules that attract eachother and move constantly.

• A solid has a definite shapeand volume.

• A liquid has a definitevolume but not a definiteshape.

• A gas does not have adefinite shape or volume. A gas takes the shape andvolume of its container.

• Pressure is a force per unitarea. Gas pressure increasesas the number of collisionsof gas particles increases.

• Boyle’s law states that thevolume of a gas increases asthe pressure decreases if thetemperature does notchange.

• Charles’s law states that thevolume of a gas increases asthe temperature increases if the pressure does notchange.

• Plasmas are composed ofparticles that have brokenapart. Plasmas do not have a definite shape or volume.

LabsFull of Hot Air! (p. 636)

Skills CheckMath ConceptsGRAPHING DATA The relation-ship between measured valuescan be seen by plotting the dataon a graph. The top graph showsthe linear relationship describedby Charles’s law—as the tempera-ture of a gas increases, its volumeincreases. The bottom graphshows the nonlinear relationshipdescribed by Boyle’s law—as thepressure of a gas increases, its volume decreases.

Visual UnderstandingPARTICLE ARRANGEMENT Many of theproperties of solids, liquids, and gases are dueto the arrangement of the atoms or moleculesof the substance. Review the models in Figure 2on page 60 to study the differences in particlearrangement between the solid, liquid, andgaseous states.

SUMMARY OF THE CHANGES OF STATEReview the table on page 72 to study the direc-tion of each change of state and whether energyis absorbed or removed during each change.

Temperature

Volu

me

Pressure

Volu

me


SECTION 2

Vocabularychange of state (p. 68)

melting (p. 69)

freezing (p. 69)

vaporization (p. 70)

boiling (p. 70)

evaporation (p. 70)

condensation (p. 71)

sublimation (p. 72)

Section Notes

• A change of state is the con-version of a substance fromone physical form to an-other. All changes of state are physical changes.

• Exothermic changes releaseenergy. Endothermic changesabsorb energy.

• Melting changes a solid to aliquid. Freezing changes aliquid to a solid. The freez-ing point and melting pointof a substance are the sametemperature.

• Vaporization changes aliquid to a gas. There are twokinds of vaporization: boilingand evaporation.

• Boiling occurs throughout aliquid at the boiling point.

• Evaporation occurs at thesurface of a liquid, at a tem-perature below the boilingpoint.

• Condensation changes a gas to a liquid.

• Sublimation changes a solid directly to a gas.

• Temperature does not change during a change of state.

LabsCan Crusher (p. 637)

A Hot and Cool Lab (p. 638)


TOPIC: Forms and Uses of Glass sciLINKS NUMBER: HSTP055

TOPIC: Solids, Liquids, and Gases sciLINKS NUMBER: HSTP060

TOPIC: Natural and Artificial Plasma sciLINKS NUMBER: HSTP065

TOPIC: Changes of State sciLINKS NUMBER: HSTP070

TOPIC: The Steam Engine sciLINKS NUMBER: HSTP075



KEYWORD: HSTSTA

75States of MatterCopyright © by Holt, Rinehart and Winston. All rights reserved.


For each pair of terms, explain the differencein meaning.

1. solid/liquid

2. Boyle’s law/Charles’s law

3. evaporation/boiling

4. melting/freezing


Multiple Choice

5. Which of the following best describes theparticles of a liquid?a. The particles are far apart and moving

fast.b. The particles are close together but

moving past each other.c. The particles are far apart and moving

slowly.d. The particles are closely packed and

vibrate in place.

6. Boiling points and freezing points areexamples ofa. chemical properties. c. energy.b. physical properties. d. matter.

7. During which change of state do atoms ormolecules become more ordered?a. boiling c. meltingb. condensation d. sublimation

8. Which of the following describes whathappens as the temperature of a gas in aballoon increases?a. The speed of the particles

decreases.b. The volume of the gas

increases and the speed of the particles increases.

c. The volume decreases.d. The pressure decreases.

9. Dew collects on a spider web in the earlymorning. This is an example ofa. condensation. c. sublimation.b. evaporation. d. melting.

10. Which of the following changes of state isexothermic?a. evaporation c. freezingb. sublimation d. melting

11. What happens to the volume of a gasinside a piston if the temperature doesnot change but the pressure is reduced?a. increasesb. stays the samec. decreasesd. not enough information

12. The atoms and molecules in mattera. are attracted to one another.b. are constantly moving.c. move faster at higher temperatures.d. All of the above

13. Which of the following contains plasma?a. dry ice c. a fireb. steam d. a hot iron

Short Answer

14. Explain why liquid water takes the shapeof its container but an ice cube does not.

15. Rank solids, liquids, and gases in order ofdecreasing particle speed.

16. Compare the density of iron in the solid,liquid, and gaseous states.


Concept Mapping

17. Use the followingterms to create a con-cept map: states ofmatter, solid, liquid,gas, plasma, changesof state, freezing,vaporization, conden-sation, melting.


18. After taking a shower, you notice thatsmall droplets of water cover the mirror.Explain how this happens. Be sure todescribe where the water comes from andthe changes it goes through.

19. In the photo below, water is being split toform two new substances, hydrogen andoxygen. Is this a change of state? Explainyour answer.

20. To protect their crops during freezing tem-peratures, orange growers spray wateronto the trees and allow it to freeze. Interms of energy lost and energy gained,explain why this practice protects theoranges from damage.

21. At sea level, water boils at 100°C, whilemethane boils at –161°C. Which of thesesubstances has a stronger force of attrac-tion between its particles? Explain yourreasoning.

MATH IN SCIENCE

22. Kate placed 100 mL of water in fivedifferent pans, placed the pans on awindowsill for a week, and measured howmuch water evaporated. Draw a graph ofher data, shown below, with surface areaon the x-axis. Is the graph linear ornonlinear? What does this tell you?

23. Examine the graph below, and answer thefollowing questions:a. What is the boiling point of the sub-

stance? What is the melting point?b. Which state is present at 30°C?c. How will the substance change if

energy is added to the liquid at 20°C?

80

Tem

pera

ture

(ºC

)

0

20

40

60

Energy

States of Matter 77

Pan number 1 2 3 4 5

Surface 44 82 20 30 65area (cm2)

Volume 42 79 19 29 62evaporated (mL)



ReadingCheck-up


78

Guiding Lightning

By the time you finish reading this sen-tence, lightning will have flashed morethan 500 times around the world. This

common phenomenon can have devastatingresults. Each year in the United States alone,lightning kills almost a hundred people andcauses several hundred million dollars in dam-age. While controlling this awesome outburst ofMother Nature may seem impossible, scientistsaround the world are searching for ways toreduce the destruction caused by lightning.

Behind the BoltsScientists have learned that during a normallightning strike several events occur. First, elec-tric charges build up at the bottom of a cloud.The cloud then emits a line of negativelycharged air particles that zigzags toward theEarth. The attraction between these negativelycharged air particles and positively charged par-ticles from objects on the ground forms aplasma channel. This channel is the pathwayfor a lightning bolt. As soon as the plasmachannel is complete, BLAM!—between 3 and 20lightning bolts separated by thousandths of asecond travel along it.

A Stroke of GeniusArmed with this information, scientists havebegun thinking of ways to redirect these

naturally occurring plasma channels. One ideais to use laser beams. In theory, a laser beamdirected into a thundercloud can charge the airparticles in its path, causing a plasma channelto develop and forcing lightning to strike.

By creating the plasma channels themselves, scientists can, in a way, catch a bolt of lightningbefore it strikes and direct it to a safe area ofthe ground. So scientists simply use lasers todirect naturally occurring lightning to strikewhere they want it to.

A Bright Future?Laser technology is not without its problems,however. The machines that generate laserbeams are large and expensive, and they canthemselves be struck by misguided lightningbolts. Also, it is not clear whether creatingthese plasma channels will be enough to pre-vent the devastating effects of lightning.

Find Out for Yourself Use the Internet or an electronic database tofind out how rockets have been used in light-ning research. Share your findings with the class.

Sometime in the future, a laser like thismight be used to guide lightning awayfrom sensitive areas.


79

Full Steam Ahead!

I t was huge. It was 40 m long, about 5 mhigh, and it weighed 245 metric tons. Itcould pull a 3.28 million kilogram train at

100 km/h. It was a 4-8-8-4 locomotive, called aBig Boy, delivered in 1941 to the Union PacificRailroad in Omaha, Nebraska. It was also oneof the final steps in a 2,000-year search to har-ness steam power.

A Simple ObservationFor thousands of years, people used wind,water, gravity, dogs, horses, and cattle toreplace manual labor. But until about 300 yearsago, they had limited success. Then in 1690,Denis Papin, a French mathematician and physi-cist, observed that steam expanding in a cylin-der pushed a piston up. As the steam thencooled and contracted, the piston fell. Watchingthe motion of the piston, Papin had an idea:attach a water-pump handle to the piston. Asthe pump handle rose and fell with the piston,water was pumped.

More Uplifting IdeasEight years later, an English naval captainnamed Thomas Savery made Papin’s devicemore efficient by using water to cool andcondense the steam. Savery’s improved pumpwas used in British coal mines. As good as

Savery’s pump was, the development of steampower didn’t stop there!

In 1712, an English blacksmith namedThomas Newcomen improved Savery’s device byadding a second piston and a horizontal beamthat acted like a seesaw. One end of the beamwas attached to the piston in the steam cylin-der. The other end of the beam was attached tothe pump piston. As the steam piston moved upand down, it created a vacuum in the pumpcylinder and sucked water up from the mine.Newcomen’s engine was the most widely usedsteam engine for more than 50 years.

Watt a Great Idea!In 1764, James Watt, a Scottish technician, wasrepairing a Newcomen engine. He realized thatheating the cylinder, letting it cool, then heatingit again wasted an enormous amount of energy.Watt added a separate chamber where thesteam could cool and condense. The two cham-bers were connected by a valve that let thesteam escape from the boiler. This improvedthe engine’s efficiency—the boiler could stay hotall the time!

A few years later, Watt turned the wholeapparatus on its side so that the piston wasmoving horizontally. He added a slide valve thatadmitted steam first to one end of the chamber(pushing the piston in one direction) and thento the other end (pushing the piston back). Thischanged the steam pump into a true steamengine that could drive a locomotive the size ofBig Boy!

Explore Other Inventions Watt’s engine helped trigger the IndustrialRevolution as many new uses for steam powerwere found. Find out more about the manyother inventors, from tinkerers to engineers,who harnessed the power of steam.


80 Chapter 4

Elements . . . . . . . . . . . 82Internet Connect . . . . . 85

Compounds . . . . . . . . . 86QuickLab . . . . . . . . . . . 87Physics Connection . . . 88Internet Connect . . . . . 89

Mixtures . . . . . . . . . . . 90MathBreak . . . . . . . . . . 94Biology Connection . . . 96Apply . . . . . . . . . . . . . 96Internet Connect . . . . . 97

Chapter Review . . . . . . . . 100

Feature Articles . . . . . 102, 103

LabBook . . . . . . . . . . . 640–645

Elements,Compounds,and Mixtures

Elements,Compounds,and Mixtures

A Groovy Kind of MixtureWhen you look at these lamps, you can easily see two dif-ferent liquids inside them. This mixture is composed ofmineral oil, wax, water, and alcohol. The water and alcohol mix, but they remain separated from the globs ofwax and oil. In this chapter, you will learn not only aboutmixtures but also about the elements and compounds that can form mixtures.


1. What is an element?2. What is a compound?

How are compounds andmixtures different?

3. What are the componentsof a solution called?


81

MYSTERY MIXTURE In this activity, you will separate the different dyes found in an inkmixture.

Procedure

1. Tear a strip of paper (about 3 cm 15 cm) from a coffee filter.Wrap one end of the strip arounda pencil so that the other end willjust touch the bottom of a clearplastic cup. Use tape to attach thepaper to the pencil.

2. Take the paper out of the cup.Using a water-soluble blackmarker, make a small dot in thecenter of the strip about 2 cmfrom the bottom.

3. Pour water in the cup to a depthof 1 cm. Carefully lower the paperinto the cup. Be sure the dot is notunder water.

4. Remove the paper when the water is1 cm from the top. Record your ob-servations in your ScienceLog.

Analysis

5. Infer what happened as the filterpaper soaked up the water.

6. Which colors were mixed to makeyour black ink?

7. Compare your results with those ofyour classmates. Record yourobservations.

8. Infer whether the process used tomake the ink involved a physical orchemical change. Explain.

Elements, Compounds, and MixturesCopyright © by Holt, Rinehart and Winston. All rights reserved.

Section

1

element nonmetalspure substance metalloidsmetals

Describe pure substances. Describe the characteristics of

elements, and give examples. Explain how elements can be

identified. Classify elements according to

their properties.

Chapter 482

ElementsImagine you are working as a lab technician for the Break-It-Down Corporation. Your job is to break down materialsinto the simplest substances you can obtain. One day a ma-terial seems particularly difficult to break down. You crushand grind it. You notice that the resulting pieces are smaller,but they are still the same material. You try other physicalchanges, including melting, boiling, and filtering it, but thematerial does not change into anything simpler.

Next you try some chemical changes. You pass an elec-tric current through the material but it still does not becomeany simpler. After recording your observations, you analyzethe results of your tests. You then draw a conclusion: thesubstance must be an element. An element is a pure sub-stance that cannot be separated into simpler substances byphysical or chemical means, as shown in Figure 1.

An Element Has Only One Type of ParticleA pure substance is a substance in which there is only onetype of particle. Because elements are pure substances, eachelement contains only one type of particle. For example, everyparticle (atom) in a 5 g nugget of the element gold is likeevery other particle of gold. The particles of a pure substanceare alike no matter where that substance is found, as shownin Figure 2. Although a meteorite might travel more than 400 million kilometers (about 248 million miles) to reach Earth,the particles of iron in a meteorite are identical to the parti-cles of iron in objects around your home!

Figure 1 No matterwhat kind of physical orchemical change youattempt, an elementcannot be changed intoa simpler substance!

Figure 2 The atoms of theelement iron are alike whetherthey are in a meteorite or in acommon iron skillet.


Every Element Has a Unique Set of PropertiesEach element has a unique set of properties that allows youto identify it. For example, each element has its own charac-teristic properties. These properties do not depend on the amountof material present in a sample of the element. Characteristicproperties include some physical properties, such as boilingpoint, melting point, and density, as well as chemical prop-erties, such as reactivity with acid. The elements helium andkrypton are unreactive gases. However, the density (mass perunit volume) of helium is less than the density of air. Therefore,a helium-filled balloon will float up if it is released. Kryptonis more dense than air, so a krypton-filled balloon will sink tothe ground if it is released.

Identifying Elements by TheirProperties Look at the elementscobalt, iron, and nickel, shown inFigure 3. Even though these threeelements have some similar prop-erties, each can be identified byits unique set of properties.

Notice that the physical prop-erties for the elements in Figure 3include melting point and den-sity. Other physical properties,such as color, hardness, and tex-ture, could be added to the list.Also, depending on the elementsbeing identified, other chemicalproperties might be useful. Forexample, some elements, such ashydrogen and carbon, are flam-mable. Other elements, such assodium, react immediately withoxygen. Still other elements, suchas zinc, are reactive with acid.

Elements, Compounds, and Mixtures 83

Figure 3 Like all other elements,cobalt, iron, and nickel can be identified by their unique combinationof properties.

Melting point is 1,495°C.Density is 8.9 g/cm3.Conducts electric current andthermal energy.Unreactive with oxygen in the air.

Cobalt

Melting point is 1,535°C.Density is 7.9 g/cm3.Conducts electric current andthermal energy.Combines slowly with oxygenin the air to form rust.

Iron

Melting point is 1,455°C.Density is 8.9 g/cm3.Conducts electric current andthermal energy.Unreactive with oxygen in the air.

Nickel


Elements Are Classified by Their PropertiesConsider how many different breeds of dogs thereare. Consider also how you tell one breed fromanother. Most often you can tell just by their appear-

ance, or what might be called physical proper-ties. Figure 4 shows several breeds of dogs,

which all happen to be terriers. Many ter-riers are fairly small in size and have shorthair. Although not all terriers are exactlyalike, they share enough common prop-erties to be classified in the same group.

Elements Are Grouped into CategoriesElements are classified into groups accord-ing to their shared properties. Recall theelements iron, nickel, and cobalt. All threeare shiny, and all three conduct thermalenergy and electric current. Using theseshared properties, scientists have groupedthese three elements, along with othersimilar elements, into one large groupcalled metals. Metals are not all exactlyalike, but they do have some propertiesin common.

If You Know the Category, You Know the Properties Ifyou have ever browsed at a music store, you know that the CDsare categorized by type of music. If you like rock-and-roll, youwould go to the rock-and-roll section. You might not recognizea particular CD, but you know that it must have the character-istics of rock-and-roll for it to be in this section.

Likewise, you can predict some of theproperties of an unfamiliar element byknowing the category to which it belongs.As shown in the concept map in Figure 5,elements are classified into three cat-egories—metals, nonmetals, and metal-loids. Cobalt, iron, and nickel are classifiedas metals. If you know that a particularelement is a metal, you know that it sharescertain properties with iron, nickel, andcobalt. The chart on the next page showsexamples of each category and describesthe properties that identify elements ineach category.

Chapter 484

Figure 4 Even though these dogs are differentbreeds, they have enough in common to be classifiedas terriers.

Metals Nonmetals Metalloids

are divided into

Elements

Figure 5 Elements are divided into three categories:metals, nonmetals, and metalloids.



1. What is a pure substance?

2. List three properties that can be used to classify elements.

3. Applying Concepts Which category of element would be the least appropriate choice for making a containerthat can be dropped without shattering? Explain yourreasoning.

REVIEW

NSTA

TOPIC: ElementsGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP085

MetalloidsMetalloids, also called semiconductors, are elementsthat have properties of both metals and nonmetals.Some metalloids are shiny, while others are dull.Metalloids are somewhat malleable and ductile. Somemetalloids conduct thermal energy and electric currentwell. Silicon is used to make computer chips. However,other elements must be added to silicon to make aworking chip.

MetalsMetals are elements that are shiny and aregood conductors of thermal energy and elec-tric current. They are malleable (they can behammered into thin sheets) and ductile (theycan be drawn into thin wires). Iron has manyuses in building and automobile construction.Copper is used in wires and coins.

The Three Major Categories of Elements

Sulfur

NonmetalsNonmetals are elements that are dull (not shiny) andthat are poor conductors of thermal energy and elec-tric current. Solid nonmetals tend to be brittle andunmalleable. Few familiar objects are made of onlynonmetals. The neon used in lights is a nonmetal, asis the graphite (carbon) used in pencils.

Neon

TinCopper

Silicon

Antimony

Lead

Bromine

Boron


Section

2

compound

Describe the properties of compounds.

Identify the differences betweenan element and a compound.

Give examples of common compounds.

Chapter 486

CompoundsMost elements take part in chemical changes fairly easily, sofew elements are found alone in nature. Instead, most elementsare found combined with other elements as compounds.

A compound is a pure substance composed of two or moreelements that are chemically combined. In a compound, a par-ticle is formed when atoms of two or more elements jointogether. In order for elements to combine, they must react, orundergo a chemical change, with one another. In Figure 6, yousee magnesium reacting with oxygen to form a compound calledmagnesium oxide. The compound is a new pure substance thatis different from the elements that reacted to form it. Mostsubstances you encounter every day are compounds. The tableat left lists some familiar examples.

Elements Combine in a Definite Ratio to Form a CompoundCompounds are not random combinations of elements. Whena compound forms, the elements join in a specific ratio accord-ing to their masses. For example, the ratio of the mass of hydro-gen to the mass of oxygen in water is always the same—1 gof hydrogen to 8 g of oxygen. This mass ratio can be writtenas 1:8 or as the fraction 1/8. Every sample of water has this1:8 mass ratio of hydrogen to oxygen. If a sample of a com-pound has a different mass ratio of hydrogen to oxygen, thecompound cannot be water.

table salt—sodium and chlorine

water—hydrogen and oxygen

sugar—carbon, hydrogen, and oxygen

carbon dioxide—carbon and oxygen

baking soda—sodium, hydrogen, carbon, and oxygen

Familiar Compounds Figure 6 As magnesium burns, it reacts with oxygenand forms the compound magnesium oxide.


Every Compound Has a Unique Set of PropertiesEach compound has a unique set of properties that allows youto distinguish it from other compounds. Like elements, eachcompound has its own physical properties, such as boilingpoint, melting point, density, and color. Compounds can alsobe identified by their different chemical properties. Some com-pounds, such as the calcium carbonate found in chalk, reactwith acid. Others, such as hydrogen peroxide, react whenexposed to light. You can see how chemical properties can beused to identify compounds in the QuickLab at right.

A compound has different properties from the elementsthat form it. Did you know that ordinary table salt is a com-pound made from two very dangerous elements? Table salt—sodium chloride—consists of sodium (which reacts violentlywith water) and chlorine (which is poisonous). Together, how-ever, these elements form a harmless compound with uniqueproperties. Take a look at Figure 7. Because a compound hasdifferent properties from the elements that react to form it,sodium chloride is safe to eat and dissolves (without explod-ing!) in water.


Self-CheckDo the properties of pure water from a glacier andfrom a desert oasis differ? (See page 724 to checkyour answer.)

Figure 7 Table salt is formed when theelements sodium and chlorine join. Theproperties of salt are different from theproperties of sodium and chlorine.

Chlorine is a poisonous,greenish yellow gas.

Sodium is a soft, silverywhite metal that reactsviolently with water.

Sodium chloride, or table salt, isa white solid that dissolves easilyin water and is safe to eat.

Compound Confusion

1. Measure 4 g (1 tsp)of compound A,and place it in aclear plastic cup.

2. Measure 4 g (1 tsp)of compound B,and place it in asecond clear plastic cup.

3. Observe the color andtexture of each compound.Record your observations.

4. Add 5 mL (1 tsp) ofvinegar to each cup.Record your observations.

5. Baking soda reacts withvinegar, while powderedsugar does not. Which ofthese compounds iscompound A, and which iscompound B?


Compounds Can Be Broken Down intoSimpler SubstancesSome compounds can be broken down into elements throughchemical changes. Look at Figure 8. When the compound mer-cury(II) oxide is heated, it breaks down into the elements mer-cury and oxygen. Likewise, if an electric current is passedthrough melted table salt, the elements sodium and chlorineare produced.

Other compounds undergo chemical changes to form sim-pler compounds. These compounds can be broken down intoelements through additional chemical changes. For example,carbonic acid is a compound that helps to give carbonated bev-erages their “fizz,” as shown in Figure 9. The carbon dioxideand water that are formed can be further broken down intothe elements carbon, oxygen, and hydrogen through additionalchemical changes.

Compounds Cannot Be Broken Down by Physical ChangesThe only way to break down a compound is through a chemi-cal change. If you pour water through a filter, the water willpass through the filter unchanged. Filtration is a physicalchange, so it cannot be used to break down a compound.Likewise, a compound cannot be broken down by being groundinto a powder or by any other physical process.

Chapter 488

The process of using electric currentto break compounds into simplercompounds and elements is knownas electrolysis. Electrolysis can beused to separate water into hydro-gen and oxygen. The elementsaluminum and copper and thecompound hydrogen peroxide are important industrial productsobtained through electrolysis.

PhysicsC O N N E C T I O N

Figure 8 Heating mercury(II)oxide causes a chemical changethat separates it into the el-ements mercury and oxygen.

Oxygen

Mercury

Mercury(II) oxide

Figure 9 Opening a carbonated drink can be messy as carbonicacid breaks down into two simplercompounds—carbon dioxide and water.


Compounds in Your WorldYou are always surrounded by compounds.Compounds make up the food you eat, theschool supplies you use, the clothes youwear—even you!

Compounds in Nature Proteins are com-pounds found in all living things. The el-ement nitrogen is needed to make proteins.Figure 10 shows how some plants get thenitrogen they need. Other plants use nitro-gen compounds that are in the soil. Animalsget the nitrogen they need by eating plantsor by eating animals that have eaten plants.As an animal digests food, the proteins inthe food are broken down into smaller com-pounds that the animal’s cells can use.

Another compound that plays an impor-tant role in life is carbon dioxide. You exhalecarbon dioxide that was made in your body.Plants take in carbon dioxide and use it tomake other compounds, including sugar.

Compounds in Industry The element nitrogen is combinedwith the element hydrogen to form a compound called ammo-nia. Ammonia is manufactured for use in fertilizers. Plants canuse ammonia as a source of nitrogen for their proteins. Othermanufactured compounds are used in medicines, food preser-vatives, and synthetic fabrics.

The compounds found in nature are usually not the rawmaterials needed by industry. Often, these compounds mustbe broken down to provide elements used as raw material. Forexample, the element aluminum, used in cans, airplanes, andbuilding materials, is not found alone in nature. It is producedby breaking down the compound aluminum oxide.


1. What is a compound?

2. What type of change is needed to break down a compound?

3. Analyzing Ideas A jar contains samples of the elementscarbon and oxygen. Does the jar contain a compound?Explain.

REVIEW

Figure 10 The bumps on theroots of this pea plant are hometo bacteria that form compoundsfrom atmospheric nitrogen. Thepea plant makes proteins fromthese compounds.

NSTA

TOPIC: CompoundsGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP090



Section

3

mixture concentrationsolution solubilitysolute suspensionsolvent colloid

Describe the properties of mixtures.

Describe methods of separatingthe components of a mixture.

Analyze a solution in terms of its solute, solvent, and concentration.

Compare the properties of solu-tions, suspensions, and colloids.

Chapter 490

MixturesHave you ever madeyour own pizza? Youroll out the dough, adda layer of tomato sauce,then add toppings likegreen peppers, mushrooms,and olives—maybe even somepepperoni! Sprinkle cheese ontop, and you’re ready to bake. Youhave just created not only a pizza butalso a mixture—and a delicious one at that!

Properties of MixturesAll mixtures—even pizza—share certain properties. A mixtureis a combination of two or more substances that are not chemi-cally combined. Two or more materials together form a mix-ture if they do not react to form a compound. For example,cheese and tomato sauce do not react when they are used tomake a pizza.

Substances in a Mixture Retain TheirIdentity Because no chemical changeoccurs, each substance in a mixturehas the same chemical makeup it had

before the mixture formed. That is, eachsubstance in a mixture keeps its iden-tity. In some mixtures, such as the pizzaabove or the piece of granite shown inFigure 11, you can even see the indi-vidual components. In other mixtures,

such as salt water, you cannot see allthe components.

Mixtures Can Be Physically Separated If you don’t likemushrooms on your pizza, you can pick them off. This is aphysical change of the mixture. The identities of the sub-stances did not change. In contrast, compounds can be bro-ken down only through chemical changes.

Not all mixtures are as easy to separate as a pizza. You can-not simply pick salt out of a saltwater mixture, but you canseparate the salt from the water by heating the mixture. Whenthe water changes from a liquid to a gas, the salt remainsbehind. Several common techniques for separating mixturesare shown on the following page.

Figure 11 Colorless quartz, pink feldspar, and black micamake up the mixture granite.



1 2 3

Distillation is a process that separates a mixturebased on the boiling points of the components.Here you see pure water being distilled from asaltwater mixture. In addition to water purifica-tion, distillation is used to separate crude oil intoits components, such as gasoline and kerosene.

A magnet can be used to separate a mixture of the

elements iron and aluminum. Iron isattracted to the

magnet, but aluminum is not.

The components that make up blood are separated using a machine called a centrifuge. This machine separates mixtures according to the densities of the components.

A mixture of the compoundsodium chloride (table salt)with the element sulfur requiresmore than one separation step.

The first step is to mix themwith another compound—water. Salt dissolves in water,but sulfur does not.

In the second step, the mix-ture is poured through a filter.The filter traps the solid sulfur.

In the third step, the sodiumchloride is separated from thewater by simply evaporatingthe water.

Common Techniques for Separating Mixtures


The Components of a Mixture Do Not Have a DefiniteRatio Recall that a compound has a specific mass ratio of theelements that form it. Unlike compounds, the components ofa mixture do not need to be combined in a definite ratio. Forexample, granite that has a greater amount of feldspar thanmica or quartz appears to have a pink color. Granite that hasa greater amount of mica than feldspar or quartz appears black. Regardless of which ratio is present, this combination ofmaterials is always a mixture—and it is always called granite.

Air is a mixture composed mostly of nitrogen and oxygen,with smaller amounts of other gases, such as carbon dioxideand water vapor. Some days the air has more water vapor, oris more humid, than on other days. But regardless of the ratioof the components, air is still a mixture.The chart at left sum-marizes the differences between mixtures and compounds.

SolutionsA solution is a mixture that appears to be a single substancebut is composed of particles of two or more substances thatare distributed evenly amongst each other. Solutions are oftendescribed as homogeneous mixtures because they have the sameappearance and properties throughout the mixture.

The process in which particles of substances separate andspread evenly throughout a mixture is known as dissolving. Insolutions, the solute is the substance that is dissolved, and thesolvent is the substance in which the solute is dissolved. Asolute is soluble, or able to dissolve, in the solvent. A substancethat is insoluble, or unable to dissolve, forms a mixture that isnot homogeneous and therefore is not a solution.

Salt water is a solution. Salt is soluble in water, meaningthat salt dissolves in water. Therefore, salt is the solute andwater is the solvent. When two liquids or two gases form asolution, the substance with the greater volume is the solvent.

Chapter 492

Mixtures vs. Compounds

Mixtures

Componentsare elements,compounds, or both

Componentskeep theiroriginal properties

Separated by physicalmeans

Formed usingany ratio ofcomponents

Compounds

Componentsare elements

Componentslose their origi-nal properties

Separated by chemicalmeans

Formed usinga set massratio of components

Many substances are solu-ble in water, including salt,sugar, alcohol, and oxygen.Water does not dissolveeverything, but it dissolvesso many different solutesthat it is often called theuniversal solvent.

REVIEW

1. What is a mixture?

2. Is a mixture separated by physical or chemical changes?

3. Applying Concepts Suggest a procedure to separate ironfilings from sawdust. Explain why this procedure works.

You may think of solutions as being liquids. And, in fact,tap water, soft drinks, gasoline, and many cleaning suppliesare liquid solutions. However, solutions may also be gases,such as air, and solids, such as steel. Alloys are solid solutionsof metals or nonmetals dissolved in metals. Brass is an alloyof the metal zinc dissolved in copper. Steel, including thatused to build the Titanic, is an alloy made of the nonmetalcarbon and other elements dissolved in iron. Look at the chartbelow for examples of the different states of matter used assolutes and solvents in solutions.

Particles in Solutions Are Extremely Small The particlesin solutions are so small that they never settle out, nor canthey be filtered out of these mixtures. In fact, the particles areso small, they don’t even scatter light. Look at Figure 12 andsee for yourself. The jar on the left contains a solution ofsodium chloride in water. The jar on the right contains a mix-ture of gelatin in water.

93

Figure 12 Both of these jarscontain mixtures. The mixture inthe jar on the left, however, is asolution. The particles in solu-tions are so small they don’tscatter light. Therefore, you can’tsee the path of light through it.

Self-CheckYellow gold is an alloymade from equal partscopper and silver com-bined with a greateramount of gold.Identify each compo-nent of yellow gold asa solute or solvent.(See page 724 to checkyour answer.)

Gas in gas Dry air (oxygen in nitrogen)

Gas in liquid Soft drinks (carbon dioxide in water)

Liquid in liquid Antifreeze (alcohol in water)

Solid in liquid Salt water (salt in water)

Solid in solid Brass (zinc in copper)

Examples of Different States in Solutions



Concentration: How Much Solute Is Dissolved? A meas-ure of the amount of solute dissolved in a solvent is concentration. Concentration can be expressed in grams ofsolute per milliliter of solvent. Knowing the exact concentra-tion of a solution is very important in chemistry and medi-cine because using the wrong concentration can be dangerous.

Solutions can be described as being concentrated or dilute.Look at Figure 13. Both solutions have the same amount ofsolvent, but the solution on the left contains less solute thanthe solution on the right. The solution on the left is dilutewhile the solution on the right is concentrated. Keep in mindthat the terms concentrated and dilute do not specify the amountof solute that is actually dissolved. Try your hand at calculat-ing concentration and describing solutions as concentrated ordilute in the MathBreak at left.

A solution that contains all the solute it can hold at a giventemperature is said to be saturated. An unsaturated solution con-tains less solute than it can hold at a given temperature. Moresolute can dissolve in an unsaturated solution.

Solubility: How Much Solute Can Dissolve? If you addtoo much sugar to a glass of lemonade, not all of the sugarcan dissolve. Some of the sugar collects on the bottom of theglass. To determine the maximum amount of sugar that candissolve, you would need to know the solubility of sugar. Thesolubility of a solute is the amount of solute needed to makea saturated solution using a given amount of solvent at a cer-tain temperature. Solubility is usually expressed in grams ofsolute per 100 mL of solvent. Figure 14 on the next page showsthe solubility of several different substances in water at dif-ferent temperatures.

Chapter 494

Figure 13 The dilute solution on the left contains less solute than the concentrated solution on the right.

Calculating ConcentrationMany solutions are colorless.Therefore, you cannot alwayscompare the concentrations ofsolutions by looking at thecolor—you have to comparethe actual calculated concen-trations. One way to calculatethe concentration of a liquidsolution is to divide the gramsof solute by the milliliters ofsolvent. For example, the con-centration of a solution inwhich 35 g of salt is dissolvedin 175 mL of water is

17535

mgL

swal

atter 0.2 g/mL

Now It’s Your TurnCalculate the concentrationsof each solution below.Solution A has 55 g of sugardissolved in 500 mL of water.Solution B has 36 g of sugardissolved in 144 mL of water.Which solution is the moredilute one? Which is themore concentrated?

MATH BREAK

Smelly solutions? Follow your nose and learn

more on page 102.


Unlike the solubility of most solids in liquids, the solubil-ity of gases in liquids decreases as the temperature is raised.Bubbles of gas appear in hot water long before the water beginsto boil. The gases that are dissolved in the water cannot remaindissolved as the temperature increases because the solubilityof the gases is lower at higher temperatures.

What Affects How Quickly Solids Dissolve in Liquids?Many familiar solutions are formed when a solid solute isdissolved in water. Several factors affect how fast the solidwill dissolve. Look at Figure 15 to see three methods used tomake a solute dissolve faster. You can see why you will enjoya glass of lemonade sooner if you stir granulated sugar intothe lemonade before adding ice!


Figure 15 Mixing, heating, and crushing iron(III) chlorideincrease the speed at which it will dissolve.

200

240

160

120

80

40

0 80 10020 40 60

Temperature (ºC)

Solu

bilit

y (g

/100

mL

of w

ater

)

Sodium chloride

Sodium nitrate

Cerium sulfate

Potassium bromide

Sodium chlorate

Figure 14 Solubility of Different Substances

The solubility of most solids increases as thetemperature gets higher. Thus, more solute can dissolve at higher temperatures. However,some solids, such as cerium sulfate, are lesssoluble at higher temperatures.

Mixing by stirring or shakingcauses the solute particles to separate from one another andspread out more quickly amongthe solvent particles.

Heating causes particles tomove more quickly. The solventparticles can separate the soluteparticles and spread them outmore quickly.

Crushing the solute increasesthe amount of contact betweenthe solute and the solvent. Theparticles of solute mix with thesolvent more quickly.



Blood is a suspension. The sus-pended particles, mainly red bloodcells, white blood cells, and platelets,are actually suspended in a solutioncalled plasma. Plasma is 90 percentwater and 10 percent dissolvedsolutes, including sugar, vitamins,and proteins.

SuspensionsWhen you shake up a snow globe, youare mixing the solid snow particleswith the clear liquid. When you stopshaking the globe, the snow parti-cles settle to the bottom of the globe.This mixture is called a suspension.A suspension is a mixture in whichparticles of a material are dispersedthroughout a liquid or gas but arelarge enough that they settle out.The particles are insoluble, so theydo not dissolve in the liquid or gas.Suspensions are often described asheterogeneous mixtures because thedifferent components are easily seen.Other examples of suspensions includemuddy water and Italian salad dressing.

The particles in a suspension are fairly large, and theyscatter or block light. This often makes a suspension difficultto see through. But the particles are too heavy to remainmixed without being stirred or shaken. If a suspension isallowed to sit undisturbed, the particles will settle out, as ina snow globe.

A suspension can be separated by passing it through a filter.The liquid or gas passes through, but the solid particles arelarge enough to be trapped by the filter, as shown in Figure 16.

Figure 16 Dirty air is a suspension that could damagea car’s engine. The air filter ina car separates dust from airto keep the dust from gettinginto the engine.

Chapter 496

Shake Well Before Use

Many medicines, such as reme-dies for upset stomach, are sus-pensions. The directions on thelabel instruct you to shake thebottle well before use. Why mustyou shake the bottle? What prob-lem could arise if you don’t?


ColloidsSome mixtures have properties of both solutionsand suspensions. These mixtures are known ascolloids (KAWL OYDZ). A colloid is a mixture inwhich the particles are dispersed throughoutbut are not heavy enough to settle out. Theparticles in a colloid are relatively small and arefairly well mixed. Solids, liquids, and gases can beused to make colloids. You might be surprised atthe number of colloids you encounter each day. Milk,mayonnaise, stick deodorant—even the gelatin andwhipped cream in Figure 17—are colloids. The materi-als that compose these products do not separatebetween uses because their particles do not settle out.

Although the particles in a colloid are much smaller thanthe particles in a suspension, they are still large enough to scat-ter a beam of light shined through the colloid, as shown inFigure 18. Finally, unlike a suspension, a colloid cannot be sepa-rated by filtration. The particles are small enough to passthrough a filter.


Figure 17 This dessert

includes two delicious exam-

ples of colloids—fruity gelatin and

whipped cream.

1. List two methods of making a solute dissolve faster.

2. Identify the solute and solvent in a solution made from15 mL of oxygen and 5 mL of helium.

3. Comparing Concepts What are three differences betweensolutions and suspensions?

REVIEW

Make a colloid found in yourkitchen on page 643 of the

LabBook.

NSTA

TOPIC: MixturesGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP095

Figure 18 The particles in the col-loid fog scatter light, making it dif-ficult for drivers to see the roadahead.

Chapter Highlights

Chapter 498

SECTION 1 SECTION 2

Skills Check

SECTION 2

Vocabularyelement (p. 82)

pure substance (p. 82)

metals (p. 85)

nonmetals (p. 85)

metalloids (p. 85)

Section Notes

• A substance in which all theparticles are alike is a puresubstance.

• An element is a pure sub-stance that cannot be bro-ken down into anythingsimpler by physical orchemical means.

• Each element has a uniqueset of physical and chemicalproperties.

• Elements are classified asmetals, nonmetals, ormetalloids, based on theirproperties.

Vocabularycompound (p. 86)

Section Notes

• A compound is a pure sub-stance composed of two ormore elements chemicallycombined.

• Each compound has aunique set of physical andchemical properties that aredifferent from the propertiesof the elements that com-pose it.

• The elements that form acompound always combinein a specific ratio accordingto their masses.

• Compounds can be brokendown into simpler sub-stances by chemicalchanges.

LabsFlame Tests (p. 640)

Visual UnderstandingTHREE CATEGORIES OF ELEMENTSElements are classified as metals,nonmetals, or metalloids, based ontheir properties. The chart on page 85provides a summary of the properties that distinguish each category.

SEPARATING MIXTURES Mixtures can beseparated through physical changes based ondifferences in the physical properties of theircomponents. Review the illustrations on page91 for some techniques for separating mixtures.

Math ConceptsCONCENTRATION The concentration of asolution is a measure of the amount of solutedissolved in a solvent. For example, a solutionis formed by dissolving 85 g of sodium nitratein 170 mL of water. The concentration of thesolution is calculated as follows:

85 g sodium nitrate= 0.5 g/mL

170 mL water


Visit the National Science Teachers Association on-lineWeb site for Internet resources related to this chapter. Justtype in the sciLINKS number for more information about thetopic:

TOPIC: The Titanic sciLINKS NUMBER: HSTP080

TOPIC: Elements sciLINKS NUMBER: HSTP085

TOPIC: Compounds sciLINKS NUMBER: HSTP090

TOPIC: Mixtures sciLINKS NUMBER: HSTP095



KEYWORD: HSTMIX

99Elements, Compounds, and Mixtures

SECTION 3

Vocabularymixture (p. 90)

solution (p. 92)

solute (p. 92)

solvent (p. 92)

concentration (p. 94)

solubility (p. 94)

suspension (p. 96)

colloid (p. 97)

Section Notes

• A mixture is a combinationof two or more substances,each of which keeps its owncharacteristics.

• Mixtures can be separatedby physical means, such asfiltration and evaporation.

• The components of a mix-ture can be mixed in anyproportion.

• A solution is a mixture thatappears to be a single sub-stance but is composed of asolute dissolved in a solvent.Solutions do not settle, can-not be filtered, and do notscatter light.

• Concentration is a measureof the amount of solute dis-solved in a solvent.

• The solubility of a solute is the amount of soluteneeded to make a saturatedsolution using a givenamount of solvent at a certain temperature.

• Suspensions are hetero-geneous mixtures that con-tain particles large enoughto settle out, be filtered, andblock or scatter light.

• Colloids are mixtures thatcontain particles too smallto settle out or be filteredbut large enough to scatterlight.

LabsA Sugar Cube Race! (p. 642)

Making Butter (p. 643)

Unpolluting Water (p. 644)


Chapter Review

Chapter 4100

Complete the following sentences by choos-ing the appropriate term from the vocabularylist to fill in each blank:

1. A ? has a definite ratio of components.

2. The amount of solute needed to form asaturated solution is the ? of thesolute.

3. A ? can be separated by filtration.

4. A pure substance must be either a(n) ? or a(n) ? .

5. Elements that are brittle and dull are ? .

6. The substance that dissolves to form asolution is the ? .


Multiple Choice

7. Which of the following increases the solu-bility of a gas in a liquid?a. increasing the temperatureb. stirringc. decreasing the temperatured. decreasing the amount of liquid

8. Which of the following best describeschicken noodle soup?a. element c. compoundb. mixture d. solution

9. Which of the following doesnot describe elements?a. all the particles are alikeb. can be broken down into simpler

substancesc. have unique sets of propertiesd. can join together to form compounds

10. A solution that contains a large amountof solute is best described asa. unsaturated. c. dilute.b. concentrated. d. weak.

11. Which of the following substances can beseparated into simpler substances only bychemical means?a. sodium c. waterb. salt water d. gold

12. Which of the following would not in-crease the rate at which a solid dissolves?a. decreasing the temperatureb. crushing the solidc. stirringd. increasing the temperature

13. An element that conducts thermal energywell and is easily shaped is aa. metal.b. metalloid.c. nonmetal.d. None of the above

14. In which classification of matter are thecomponents chemically combined?a. alloy c. compoundb. colloid d. suspension

Short Answer

15. What is the difference between an element and a compound?

16. When nail polish is dissolved in acetone,which substance is the solute and whichis the solvent?

100

USING VOCABULARY



101Elements, Compounds, and Mixtures

Concept Mapping

17. Use the followingterms to create aconcept map: matter, element,compound, mixture,solution, suspension,colloid.

18. Describe a procedure to separate a mixtureof salt, finely ground pepper, and pebbles.

19. A light green powder isheated in a test tube. Agas is given off, whilethe solid becomes black.In which classificationof matter does the greenpowder belong? Explainyour reasoning.

20. Why is it desirable to know the exact concentration of solutionsrather than whether they are concentratedor dilute?

21. Explain the three properties of mixturesusing a fruit salad as an example.

22. To keep the “fizz” in carbonated beveragesafter they have been opened, should youstore them in a refrigerator or in a cabi-net? Explain.

MATH IN SCIENCE

23. What is the concentration of a solutionprepared by mixing 50 g of salt with 200 mL of water?

24. How many grams of sugar must be dis-solved in 150 mL of water to make a solu-tion with a concentration of 0.6 g/mL?


25. Use Figure 14 on page 67 to answer thefollowing questions:a. Can 50 g of sodium chloride dissolve in

100 mL of water at 60°C?b. How much cerium sulfate is needed to

make a saturated solution in 100 mL ofwater at 30°C?

c. Is sodium chloride or sodium nitratemore soluble in water at 20°C?

26. Dr. Sol Vent tested the solubility of acompound. The data below was collectedusing 100 mL of water. Graph Dr. Vent’sresults. To increase the solubility, wouldyou increase or decrease the temperature?Explain.

27. What type of mixture is shown in thephoto below? Explain.

Temperature (°C) 10 25 40 60 95

Dissolved solute (g) 150 70 34 25 15

101


MATH IN SCIENCE




ReadingCheck-up


102

Perfume: Fragrant Solutions

Making perfume is an ancient art. It waspracticed, for example, by the ancientEgyptians, who rubbed their bodies

with a substance made by soaking fragrantwoods and resins in water and oil. From certainreferences and formulas in the Bible, we knowthat the ancient Israelites also practiced the artof perfume making. Other sources indicate thatthis art was also known to the early Chinese,Arabs, Greeks, and Romans.

Only the E-scent-ialsOver time, perfume making has developed intoa complicated art. A fine perfume may containmore than 100 different ingredients. The mostfamiliar ingredients come from fragrant plantsor flowers, such as sandalwood or roses. Theseplants get their pleasant odor from their essen-tial oils, which are stored in tiny, baglike partscalled sacs. The parts of plants that are used forperfumes include the flowers, roots, and leaves.Other perfume ingredients come from animalsand from man-made chemicals.

Making ScentsPerfume makers first remove essential oils fromthe plants using distillation or reactions withsolvents. Then the essential oils are blendedwith other ingredients to create perfumes.Fixatives, which usually come from animals,make the other odors in the perfume lastlonger. Oddly enough, most natural fixativessmell awful! For example, civet musk is a foul-smelling liquid that the civet cat sprays on itsenemies.

Taking NotesWhen you take a whiff from a bottle of per-fume, the first odor you detect is called the topnote. It is a very fragrant odor that evaporatesrather quickly. The middle note, or modifier,adds a different character to the odor of thetop note. The base note, or end note, is theodor that lasts the longest.

Smell for Yourself Test a number of different perfumes andcolognes to see if you can identify three differ-ent notes in each.

Perfumes have been found in the tombs of Egyptians who lived more than 3,000 years ago.

Not all perfume ingredients smell good. Thefoul-smelling oil from the African civet catis used as a fixative in some perfumes.


103

“The Strange Case of Dr. Jekyll and

Mr. Hyde”by Robert Louis Stevenson

Avicious, detestable man murders an old gentleman. A wealthy and respectablescientist commits suicide. Are these two

tragedies connected in some way?Dr. Henry Jekyll is an admirable member of

society. He is a doctor and a scientist. Althoughwild as a young man, Jekyll has become coldand analytical as he has aged and has pursuedhis scientific theories. Now he wants to under-stand the nature of human identity. He wants toexplore the different parts of the human person-ality that usually fit together smoothly to make acomplete person. His theory is that if he canseparate his personality into “good” and “evil”parts, he can get rid of his evil side and lead ahappy, useful life. So Jekyll develops a chemicalmixture that will allow him to test his theory.The results are startling!

Who is the mysterious Mr. Hyde? He is not ascientist. He is a man of action and anger, whosparks fear in the hearts of those he comes incontact with. Where did he come from? Whatdoes he do? How can local residents be pro-tected from his wrath?

Robert Louis Stevenson’s story of the decentdoctor Henry Jekyll and the violent Edward Hydeis a classic science-fiction story. When Jekyllmixes his “salts” and drinks his chemical mix-ture, he changes his life—and Edward Hyde’s—completely. To find out more, read Stevenson’s“The Strange Case of Dr. Jekyll and Mr. Hyde” inthe Holt Anthology of Science Fiction.


T I M E L I N E

U N I T Motion and Forces

Unit 2104

2t’s hard to imagine aworld where nothing

ever moves. Withoutmotion or forces tocause motion, lifewould be very dull!The relationshipbetween force andmotion is the subjectof this unit. You willlearn how to describethe motion of objects,how forces affectmotion, and how fluids exert force. Thistimeline shows someevents and discoveriesthat have occurred asscientists have workedto understand themotion of objects hereon Earth and in space.

I

Around

250 B.C.Archimedes, a Greek mathematician,develops the principle that bears hisname. The principle relates the buoy-

ant force on an object in a fluid to theamount of fluid the object displaces.

1905While employed as a patent clerk, German

physicist Albert Einstein publishes his special theory of relativity. The theory

states that the speed of light is constant, no matter what the reference point is.

1921Bessie Coleman becomes the firstAfrican-American woman licensed

to fly an airplane.

1947While flying a Bell X-1 rocket-poweredairplane, American pilot Chuck Yeager

becomes the first human to travelfaster than the speed of sound.

Around

240 B.C.Chinese astronomers are

the first to record a sightingof Halley’s Comet.


105Motion and Forces

1687Sir Isaac Newton, a British

mathematician and scientist,publishes Principia, abook describing hislaws of motion andthe law of universal

gravitation.

1846After determining that the orbit

of Uranus is different from what ispredicted from the law of

universal gravitation, scientists discover Neptune, shown here,

whose gravitational force is causingUranus’s unusual orbit.

1990The Magellan spacecraft beginsorbiting Venus for a four-year

mission to map the planet. Thespacecraft uses the sun’s gravita-tional force to propel it to Venus

without burning much fuel.

1971American astronaut

Alan Shepard takes abreak from gatheringlunar data to play golfon the moon during

the Apollo 14 mission.

1999NASA launches the MarsPolar Lander spacecraft, one of a series sent to

explore Mars.

1764In London, Wolfgang

Amadeus Mozartcomposes his firstsymphony—at the

age of 9.

1519Portuguese explorer Ferdinand

Magellan begins the first voyagearound the world.


106 Chapter 5

Measuring Motion . . . 108MathBreak . . . . . 109, 113Internet Connect . . . . 114

What Is a Force? . . . . 115

Friction: A Force ThatOpposes Motion . . . . 119

QuickLab . . . . . . . . . . 120Apply . . . . . . . . . . . . . 124Internet Connect . . . . 124

Gravity: A Force ofAttraction . . . . . . . . . . 125

Biology Connection . . 125Astronomy Connection . . . . . . . . 127

Internet Connect . . . . 129

Chapter Review . . . . . . . . . . 132

Feature Articles . . . . . . 134, 135

LabBook . . . . . . . . . . . 646–651

Matter in MotionMatter in Motion

Swoosh!!Have you ever watched a speed skating race during theWinter Olympics? Speed skaters are extremely fast. In fact,some speed skaters have been known to skate at a rate of12 meters per second! Speed skaters, like the one you see inthis photograph, must have a great deal of athletic skill andability. First of all, they have to be very strong in order toexert the force needed to move so fast. Secondly, speedskaters skate on ice, which is very slippery. These athletesmust be able to overcome the lack of friction between theirskates and the ice—so they won’t fall during the race! Inthis chapter, you will learn more about motion, includingspeed and acceleration, and the forces that affect motion,such as friction and gravity.


1. How is motion measured? 2. What is a force?3. How does friction affect

motion? 4. How does gravity affect

objects?


107

THE DOMINO DERBYSpeed is the rate at which an objectmoves. In this activity, you willdetermine the factors that affect the speed of falling dominoes.

Procedure

1. Set up 25 dominoes in a straightline. Try to keep equal spacingbetween the dominoes.

2. Using a meterstick, measure the total length of your row ofdominoes, and write it down.

3. Using a stopwatch, time how long it takes for the entire row of dominoes to fall. Record thismeasurement.

4. Repeat steps 2 and 3 severaltimes, using distances between the dominoes that are smaller andlarger than the distance used inyour first setup.

Analysis

5. Calculate the average speed foreach trial by dividing the totaldistance (the length of the dominorow) by the time taken to fall.

6. How did the spacing betweendominoes affect the averagespeed? Is this result what youexpected? If not, explain.

Matter in MotionCopyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 5108

Measuring MotionLook around you—you’re likely to see something in motion.Your teacher may be walking across the room, or perhaps abird is flying outside a window. Even if you don’t see any-thing moving, motion is still occurring all around you. Tinyair particles are whizzing around, the moon is circling theEarth, and blood is traveling through your veins and arteries!

Observing Motion You might think that the motion of an object is easy to detect—you just observe the object. But you actually must observe theobject in relation to another object that appears to stay inplace. The object that appears to stay in place is a referencepoint. When an object changes position over time when com-pared with a reference point, the object is in motion. Whenan object is in motion, you can describe the direction of itsmotion with a reference direction, such as north, south, east,west, or up and down.

Common Reference Points The Earth’s surface is a com-mon reference point for determining position and motion.Nonmoving objects on Earth’s surface, such as buildings, trees,and mountains, are also useful reference points, as shown inFigure 1.

A moving object can also be used as a reference point. Forexample, if you were on the hot-air balloon shown below, youcould watch a bird fly by and see that it was changing posi-tion in relation to your moving balloon. Furthermore, Earthitself is a moving reference point—it is moving around the sun.

Figure 1 During the time ittook for these pictures to betaken, the hot-air balloonchanged position comparedwith a reference point—themountain.

Section

1

motion velocityspeed acceleration

Identify the relationship between motion and a reference point.

Identify the two factors thatspeed depends on.

Determine the differencebetween speed and velocity.

Analyze the relationship ofvelocity to acceleration.

Interpret a graph showing acceleration.


Speed Depends on Distance and TimeThe rate at which an object moves is its speed. Speed dependson the distance traveled and the time taken to travel that dis-tance. Look back at Figure 1. Suppose the time interval betweenthe pictures was 10 seconds and the balloon traveled 50 m inthat time. The speed (distance divided by time) of the balloonis 50 m/10 s, or 5 m/s.

The SI unit for speed is meters per second (m/s). Kilometersper hour, feet per second, and miles per hour are other unitscommonly used to express speed.

Determining Average Speed Most of the time, objects donot travel at a constant speed. For example, you probably donot walk at a constant speed from one class to the next.Therefore, it is very useful to calculate average speed using thefollowing equation:

Average speed

Recognizing Speed on a Graph Suppose a person drivesfrom one city to another. The blue line in the graph belowshows the distance traveled every hour. Notice that the dis-tance traveled every hour is different. This is because the speed(distance/time) is not constant—the driver changes speed oftenbecause of weather, traffic, or varying speed limits. The aver-age speed can be calculated by adding up the total distanceand dividing it by the total time:

Average speed 90 km/h

The red line shows the average distance traveled each hour.The slope of this line is the average speed.

360 km

4 h

total distance

total time

Matter in Motion 109

AverageDistance

Time (h)

400

300

200

100

0 1 2 3 4

Dis

tanc

e (k

m)

Distance

A Graph Showing Distance over Time

Calculating Average SpeedPractice calculating averagespeed in the problems listedbelow:

1. If you walk for 1.5 hoursand travel 7.5 km, what isyour average speed?

2. A bird flies at a speed of15 m/s for 10 s, 20 m/sfor 10 s, and 25 m/s for 5 s. What is the bird’s average speed?

MATH BREAK

The list below shows a com-parison of some interestingspeeds:

Cockroach . . . . . . 1.25 m/s

Kangaroo . . . . . . . . . 15 m/s

Cheetah (the fastest land animal) . . . . . . . 27 m/s

Sound (in air) . . . . . 343 m/s

Space shuttle . . . 10,000 m/s

Light . . . . . 300,000,000 m/s

A Graph Showing Distance over Time



Velocity: Direction Matters

Have you figured it out? The birds traveled at the samespeeds for the same amounts of time, but they did not end upat the same place because they went in different directions. In

other words, they had differentvelocities. The speed of an objectin a particular direction is theobject’s velocity (vuh LAHS uh tee).

Be careful not to confuse theterms speed and velocity; they donot mean the same thing. Becausevelocity must include direction, itwould not be correct to say thatan airplane’s velocity is 600 km/h.However, you could say theplane’s velocity is 600 km/hsouth. Velocity always includes a reference direction. Figure 2further illustrates the differencebetween speed and velocity.

Velocity Changes as Speed or Direction Changes You canthink of velocity as the rate of change of an object’s position.An object’s velocity is constant only if its speed and directiondon’t change. Therefore, constant velocity is always along astraight line. An object’s velocity will change if either its speedor direction changes. For example, if a bus traveling at 15 m/s south speeds up to 20 m/s, a change in velocity hasoccurred. But a change in velocity also occurs if the bus con-tinues to travel at the same speed but changes direction totravel east.

Chapter 5110

Here’s a riddle for you: Two birds leave the sametree at the same time. They both fly at 10 km/hfor 1 hour, 15 km/h for 30 minutes, and 5 km/h for 1 hour. Why don’t they end up at the same destination?

Figure 2 The speeds of thesecars may be similar, but theirvelocities are different becausethey are going in different directions.

Self-CheckWhich of the following are examples of velocity?

1. 25 m/s forward 3. 55 m/h south

2. 1,500 km/h 4. all of the above

(See page 724 to check your answer.)


Combining Velocities If you’re riding in a bus traveling eastat 15 m/s, you and all the other passengers are also travelingat a velocity of 15 m/s east. But suppose you stand up andwalk down the bus’s aisle while it is moving. Are you still moving at the same velocity as the bus? No! Figure 3shows how you can combine velocities to determine the resultant velocity.


1. What is a reference point?

2. What two things must you know to determine speed?

3. What is the difference between speed and velocity?

4. Applying Concepts Explain why it is important to knowa tornado’s velocity and not just its speed.

When you combinetwo velocities that arein the same direction,add them together tofind the resultantvelocity.

When you combinetwo velocities that arein opposite directions,subtract the smallervelocity from the largervelocity to find theresultant velocity. Theresultant velocity is inthe direction of thelarger velocity.

The space shuttle is alwayslaunched in the same direc-tion that the Earth rotates,thus taking advantage of theEarth’s rotational velocity(over 1,500 km/h east). Thisallows the shuttle to use lessfuel to reach space than if ithad to achieve such a greatvelocity on its own.

REVIEW

Person’s resultant velocity

15 m/s east + 1 m/s east = 16 m/s east

Person’s resultant velocity

15 m/s east – 1 m/s west = 14 m/s east

Figure 3 Determining Resultant Velocity

1 m/s east

1 m/s west

15 m/s east

15 m/s east


Acceleration: The Rate at WhichVelocity ChangesImagine that you are in-line skating and you see a large rockin your path. You slow down and swerve to avoid the rock.

A neighbor sees you and exclaims, “That was greatacceleration! I’m amazed that you could slow

down and turn so quickly!” You’re puzzled.Doesn’t accelerate mean to speed up? But

you didn’t speed up—you slowed downand turned. So how could you have accelerated?

Defining Acceleration Althoughthe word accelerate is commonlyused to mean “speed up,” there’smore to its meaning scientifically.Acceleration (ak SEL uhr AY shuhn)is the rate at which velocity changes.To accelerate means to change veloc-ity. You just learned that velocitychanges if speed changes, direction

changes, or both. So your neighborwas right! Your speed and direction

changed, so you accelerated.Keep in mind that acceleration is not

just how much velocity changes. It is alsohow fast velocity changes. The faster velocity

changes, the greater the acceleration is.

Calculating Acceleration You can calculate acceleration byusing the following equation:

Acceleration

Velocity is expressed in meters per second (m/s), and timeis expressed in seconds (s). Therefore, acceleration is expressedin meters per second per second (m/s/s).

Suppose you get on your bicycle and accelerate southwardat a rate of 1 m/s/s. (Like velocity, acceleration has size anddirection.) This means that every second, your southward veloc-ity increases by 1 m/s, as shown in Figure 4 on the next page.

final velocity starting velocitytime it takes to change velocity

Chapter 5112

Use this simpledevice to “see”acceleration onpage 647 of theLabBook.


After 1 second, you have a velocity of 1 m/s south, as shownin Figure 4. After 2 seconds, you have a velocity of 2 m/s south. After 3 seconds, you have a velocity of 3 m/ssouth, and so on. If your final velocity after 5 seconds is 5 m/s south, your acceleration can be calculated as follows:

Acceleration 1 m/s/s south

You can practice calculating acceleration by doing theMathBreak shown here.

Examples of Acceleration In the example above, your veloc-ity was originally zero and then it increased. Because yourvelocity changed, you accelerated. Acceleration in which veloc-ity increases is sometimes called positive acceleration.

Acceleration also occurs when velocity decreases. In theskating example, you accelerated because you slowed down.Acceleration in which velocity decreases is sometimes callednegative acceleration or deceleration.

Remember that velocity has direction, so velocity willchange if your direction changes. Therefore, a change in direc-tion is acceleration, even if there is no change in speed. Somemore examples of acceleration are shown in the chart below.

5 m/s 0 m/s

5s


Figure 4 Acceleration at 1 m/s/s South

1 m/s 2 m/s 3 m/s 4 m/s 5 m/s

A plane taking off Increase in speed

A car stopping at a stop sign Decrease in speed

Jogging on a winding trail Change in direction

Driving around a corner Change in direction

Standing at Earth’s equator Change in direction

Calculating AccelerationUse the equation shown onthe previous page to do thefollowing problems. Be sureto express your answers inm/s/s and include direction.

1. A plane passes overPoint A with a velocity of 8,000 m/s north. Forty seconds later it passes over Point B at a velocityof 10,000 m/s north. Whatis the plane’s accelerationfrom A to B?

2. A coconut falls from thetop of a tree and reaches avelocity of 19.6 m/s whenit hits the ground. It takes2 seconds to reach theground. What is thecoconut’s acceleration?

MATH BREAK

Example of Acceleration How Velocity Changes


Circular Motion: Continuous Acceleration Does it surpriseyou to find out that standing at Earth’s equator is an exam-ple of acceleration? After all, you’re not changing speed, andyou’re not changing direction . . . or are you? In fact, you aretraveling in a circle as the Earth rotates. An object travelingin a circular motion is always changing its direction. Therefore,its velocity is always changing, so acceleration is occurring.The acceleration that occurs in circular motion is known ascentripetal (sen TRIP uht uhl) acceleration. Another example ofcentripetal acceleration is shown in Figure 5.

Recognizing Acceleration on a Graph Suppose that youhave just gotten on a roller coaster. The roller coaster movesslowly up the first hill until it stops at the top. Then you’reoff, racing down the hill! The graph below shows your acceleration for the 10 seconds coming down the hill. You cantell from this graph that your acceleration is positive becauseyour velocity increases as time passes. Because the graph is nota straight line, you can also tell that your acceleration is not constant for each second.

Chapter 5114

1. What is acceleration?

2. Does a change in direction affect acceleration? Explainyour answer.

3. Interpreting Graphics How do you think a graph of decel-eration would differ from the graph shown above? Explainyour reasoning.

REVIEW

Time (seconds)

25

20

15

10

5

0 1 2 3 4 5 6 7 8 9 10

Velo

city

(m

/s)

A Graph Showing Acceleration

Figure 5 The blades of this windmill are constantlychanging direction as theytravel in a circle. Thus, cen-tripetal acceleration isoccurring.

A Graph Showing Acceleration

NSTA

TOPIC: Measuring MotionGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP105

What Is a Force?You often hear the word force in everyday conversation:

“That storm had a lot of force!”“Our basketball team is a force to be reckoned with.”

“A flat tire forced me to stop riding my bicycle.”“The inning ended with a force-out at second base.”

But what exactly is a force? In science, a force is simply apush or a pull. All forces have both size and direction.

Forces are everywhere. In fact, any time you see somethingmoving, you can be sure that its motion was created by a force. Scientists express force using a unit called the newton (N). The more newtons, the greater the force.

Forces Act on ObjectsAll forces are exerted by one object on another object. For anypush to occur, something has to receive the push. You can’tpush nothing! The same is true for any pull. When doing school-work, you use your fingers to pull open books or to push thebuttons on a computer keyboard. In these examples, your fin-gers are exerting forces on the books and the keys. However,just because a force is being exerted by one object on anotherdoesn’t mean that motion will occur. For example, you areprobably sitting on a chair as you read this. But the force youare exerting on the chair does not cause the chair to move.

That’s because the Earth is also exerting aforce on the chair. In most cases, it is easyto determine where the push or pull is com-ing from, as shown in Figure 6.

Figure 6 It is obvious that the bulldozeris exerting a force on the pile of soil. Butdid you know that the pile of soil also

exerts a force, even whenit is just sitting on

the ground?


Section

2

force net forcenewton

Give examples of different kindsof forces.

Determine the net force on anobject.

Compare balanced and unbal-anced forces.



It is not always so easy to tell what is exertinga force or what is receiving a force, as shown in

Figure 7. You cannot see what exerts the force thatpulls magnets to refrigerators, and the air you breathe

is an unseen receiver of a force called gravity. You willlearn more about gravity later in this chapter.

Forces in CombinationOften more than one force is exerted on an object at thesame time. The net force is the force that results fromcombining all the forces exerted on an object. So how doyou determine the net force? The examples below canhelp you answer this question.

Forces in the Same Direction Suppose you and afriend are asked to move a piano for the music teacher.To do this, you pull on one end of the piano, and yourfriend pushes on the other end. Together, your forcesadd up to enough force to move the piano. This is becauseyour forces are in the same direction. Figure 8 shows thissituation. Because the forces are in the same direction,they can be added together to determine the net force.In this case, the net force is 45 N, which is plenty tomove a piano—if it is on wheels, that is!

Chapter 5116

Figure 8 When the forcesare in the same direction,you add the forces togetherto determine the net force.

Net force25 N 20 N 45 N

to the right

25 N 20 N

Figure 7Something unseen exerts a force that makes your socks cling together when they come out of the dryer. You have to exert a force to separate the socks.


Forces in Different Directions Consider two dogs playingtug of war with a short piece of rope. Each is exerting a force,but in opposite directions. Figure 9 shows this scene. Noticethat the dog on the left is pulling with a force of 10 N andthe dog on the right is pulling with a force of 12 N. Whichdog do you think will win the tug of war?

Because the forces are in opposite directions, the net forceis determined by subtracting the smaller force from the largerone. In this case, the net force is 2 N in the direction of thedog on the right. Give that dog a dog biscuit!

Unbalanced and Balanced ForcesIf you know the net force on an object, you can determinethe effect the force will have on the object’s motion. Why?The net force tells you whether the forces on the object arebalanced or unbalanced.

Unbalanced Forces Produce a Change in Motion In theexamples shown in Figures 8 and 9, the net force on the objectis greater than zero. When the net force on an object is notzero, the forces on the object are unbalanced. Unbalanced forcesproduce a change in motion (acceleration). In the two previ-ous examples, the receivers of the forces—the piano and therope—move. Unbalanced forces are necessary to cause a non-moving object to start moving.


Self-CheckWhat is the net forcewhen you combine aforce of 7 N north witha force of 5 N south?(See page 724 to checkyour answer.)

Net force12 N 10 N 2 N

to the right

10 N 12 N

Every moment, forces in severaldirections are exerted on the GoldenGate Bridge. For example, Earthexerts a powerful downward forceon the bridge while elastic forcespull and push portions of the bridgeup and down. To learn how thebridge stands up to these forces,turn to page 135.

ScienceC O N N E C T I O N

Figure 9 When the forces are in differ-ent directions, you subtract the smallerforce from the larger force to determinethe net force.


Unbalanced forces are also necessary to change the motionof moving objects. For example, consider a soccer game. Thesoccer ball is already moving when it is passed from one playerto another. When the ball reaches the second player, the playerexerts an unbalanced force—a kick—on the ball. After the kick,the ball moves in a new direction and with a new speed.

Keep in mind that an object can continue to move evenwhen the unbalanced forces are removed. A soccer ball, forexample, receives an unbalanced force when it is kicked.However, the ball continues to roll along the ground long afterthe force of the kick has ended.

Balanced Forces Produce No Change in Motion Whenthe forces applied to an object produce a net force of zero, theforces are balanced. Balanced forces do not cause a nonmov-ing object to start moving. Furthermore, balanced forces willnot cause a change in the motion of a moving object.

Many objects around you have only balanced forces act-ing on them. For example, a light hanging from the ceilingdoes not move because the force of gravity pulling downon the light is balanced by an elastic force due to tensionthat pulls the light up. A bird’s nest in a tree and a hatresting on your head are also examples of objects withonly balanced forces acting on them. Figure 10 shows

another case where the forces on an object arebalanced. Because all the forces are balanced,

the house of cards does not move.

Chapter 5118

REVIEW

1. Give four examples of a force being exerted.

2. Explain the difference between balanced and unbalancedforces and how each affects the motion of an object.

3. Interpreting Graphics In the picture at left, two bighornsheep push on each other’s horns. The arrow shows thedirection the two sheep are moving. Describe the forcesthe sheep are exerting and how the forces combine toproduce the sheep’s motion.

Figure 10 The forces on this house ofcards are balanced. An unbalanced forceon one of the cards would cause motion—and probably a mess!



Friction: A Force ThatOpposes MotionPicture a warm summer day. You are enjoying the day by wear-ing shorts and tossing a ball with your friends. By accident,one of your friends tosses the ball just out of your reach. Youhave to make a split-second decision to dive for it or not. Youlook down and notice that if you dove for it, you would mostlikely slide across pavement rather than the surrounding grass.What would you decide?

Unless you enjoy scraped knees, you probablywould not want to slide on the pavement.

The painful difference between slid-ing on grass and sliding on pave-

ment has to do with friction.Friction is a force that opposesmotion between two surfacesthat are touching.

The Source of FrictionFriction occurs because the surface of any object is rough. Evensurfaces that look or feel very smooth are actually covered withmicroscopic hills and valleys. When two surfaces are in con-tact, the hills and valleys of one surface stick to the hills andvalleys of the other surface, as shown in Figure 11. This con-tact causes friction even when the surfaces appear smooth.

The amount of friction between two surfaces depends onmany factors, including the roughness of the surfaces and theforce pushing the surfaces together.

Figure 11 When the hills and valleys ofone surface stick to the hills and valleysof another surface, friction is created.

Section

3

friction

Explain why friction occurs. List the types of friction, and

give examples of each. Explain how friction can be both

harmful and helpful.


Rougher Surfaces Create More Friction Rougher surfaceshave more microscopic hills and valleys. Thus, the rougherthe surface, the greater the friction. Think back to the exam-ple on the previous page. Pavement is much rougher thangrass. Therefore, more friction is produced when you slide onthe pavement than when you slide on grass. This increasedfriction is more effective at stopping your sliding, but it is alsomore painful! On the other hand, if the surfaces are smooth,there is less friction. If you were to slide on ice instead of ongrass, your landing would be even more comfortable—but alsomuch colder!

Greater Force Creates More Friction The amount of fric-tion also depends on the force pushing the surfaces together.If this force is increased, the hills and valleys of the surfacescan come into closer contact. This causes the friction betweenthe surfaces to increase. Less massive objects exert less forceon surfaces than more massive objects do, as illustrated inFigure 12. However, changing the amounts of the surfaces thattouch does not change the amount of friction.

Chapter 5120

Figure 12 Force and Friction

There is more frictionbetween the more massive book and the table than there is between the less massive book and thetable. A harder push is needed to overcome friction to move the more massive book.

Force of friction

Force needed to overcome friction

Force of friction

Force needed to overcome friction

Turning the more massive book on its edge does not change the amount of frictionbetween the table and the book.

a

b

The Friction 500

1. Make a short ramp out ofa piece of cardboard andone or two books on atable.

2. Put a toy car at the top ofthe ramp and let go. Ifnecessary, adjust the rampheight so that your cardoes not roll off the table.

3. Put the car at the top ofthe ramp again and let go.Record the distance the cartravels after leaving theramp. Do this three times,and calculate the averagefor your results.

4. Change the surface of thetable by covering it withsandpaper or cloth.Repeat step 3. Change thesurface one more time,and repeat step 3 again.

5. Which surface had themost friction? Why? Whatdo you predict would hap-pen if the car were heav-ier? Record your resultsand answers in yourScienceLog.


Types of Friction The friction you observe when sliding books across a tabletopis called sliding friction. Other types of friction include rollingfriction, fluid friction, and static friction. As you will learn,the name of each type of friction is a big clue as to the con-ditions where it can be found.

Sliding Friction If you push aneraser across your desk, the eraserwill move for a short distance andthen stop. This is an example of slid-ing friction. Sliding friction is veryeffective at opposing the movementof objects and is the force that causesthe eraser to stop moving. You canfeel the effect of sliding frictionwhen you try to move a heavydresser by pushing it along the floor.You must exert a lot of force to over-come the sliding friction, as shownin Figure 13.

You use sliding friction whenyou go sledding, when you applythe brakes on a bicycle or a car, or when you write with a piece of chalk.

Rolling Friction If the same heavydresser were on wheels, you wouldhave an easier time moving it. Thefriction between the wheels and thefloor is an example of rolling friction.The force of rolling friction is usu-ally less than the force of sliding fric-tion. Therefore, it is generally easierto move objects on wheels than itis to slide them along the floor, asshown at right.

Rolling friction is an importantpart of almost all means of trans-portation. Anything with wheels—bicycles, in-line skates, cars, trains,and planes—uses rolling frictionbetween the wheels and the groundto move forward.


Moving a heavy piece of furniture in your room can behard work because the forceof sliding friction is large.

Figure 13 Comparing Sliding Friction and Rolling Friction

It is easier to move a heavy pieceof furniture if you put it on wheels.The force of rolling friction issmaller and easier to overcome.


Fluid Friction Why is it harder to walk on afreshly mopped floor than on a dry floor? Thereason is that on the wet floor the sliding fric-tion between your feet and the floor is replacedby fluid friction between your feet and the water.In this case, fluid friction is less than slidingfriction, so the floor is slippery. The term fluidincludes liquids, such as water and milk, andgases, such as air and helium.

Fluid friction opposes the motion of objectstraveling through a fluid, as illustrated inFigure 14. For example, fluid friction betweenair and a fast moving car is the largest forceopposing the motion of the car. You can observethis friction by holding your hand out the window of a moving car.

Static Friction When a force is applied to anobject but does not cause the object to move,static friction occurs. The object does not movebecause the force of static friction balances theforce applied. Static friction disappears as soonas an object starts moving, and then anothertype of friction immediately occurs. Look atFigure 15 to understand when static frictionaffects an object.

Chapter 5122

There is no frictionbetween the blockand the table whenno force is appliedto the block tomove it.

If a small force—shown inblue—is exerted on the block,the block does not move. Theforce of static friction—shownin orange—exactly balancesthe force applied.

When the force exerted on the block isgreater than the force of static friction,the block starts moving. Once theblock starts moving, all static friction isgone, and the force applied opposessliding friction—shown in green.

Figure 15 Static Friction

Figure 14 Swimming provides a good workoutbecause you must exert force to overcome fluidfriction.

Self-CheckWhat type of friction was involved in the imaginarysituation at the beginning of this section? (See page724 to check your answer.)

Force applied

Static friction

Force applied

Sliding friction

a b c


Friction Can Be Harmful or HelpfulThink about how friction affects a car. Without friction, thetires could not push against the ground to move the car for-ward and the brakes could not stop the car. Without friction,a car is useless. However, friction can cause problems in a cartoo. Friction between moving engine parts increases their tem-perature and causes the parts to wear down. A liquid coolantis added to the engine to keep it from overheating, and engineparts need to be changed as they wear out.

Friction is both harmful and helpful to you and the worldaround you. Friction can cause holes in your socks and in theknees of your jeans. Friction by wind and water can cause ero-sion of the topsoil that nourishes plants. On the other hand,friction between your pencil and your paper is necessary forthe pencil to leave a mark. Without friction, you would justslip and fall when you tried to walk. Because friction can beboth harmful and helpful, it is sometimes necessary to reduceor increase friction.

Some Ways to Reduce Friction One way to reduce frictionis to use lubricants. Lubricants (LOO bri kuhnts) are substancesthat are applied to surfaces to reduce the friction between them.Some examples of common lubricants are motor oil, wax, andgrease. Figure 16 shows why lubricants are important to main-taining car parts.

Friction can also be reduced by switching from sliding fric-tion to rolling friction. Ball bearings are placed between thewheels and axles of in-line skates and bicycles to make it easierfor the wheels to turn by reducing friction.


Lubricants are usually liquids, but they can besolids or gases too.Graphite is a shiny blacksolid that is used in pencils.Graphite dust is very slip-pery and is often used as alubricant for ball bearingsin bicycle and skate wheels.An example of a gas lubri-cant is the air that comesout of the tiny holes of anair-hockey table.

Have some fun with friction!Investigate three types of

friction on page 650 of theLabBook.

Figure 16 Motor oil is used as a lubricant incar engines. Without oil, engine parts wouldwear down quickly, as the connecting rod on the bottom has.


Another way to reduce friction is to make surfaces that rubagainst each other smoother. For example, rough wood on apark bench is painful to slide across because there is a largeamount of friction between your leg and the bench. Rubbingthe bench with sandpaper makes it smoother and more com-fortable to sit on because the friction between your leg and thebench is reduced.

Some Ways to Increase Friction One way to increase fric-tion is to make surfaces rougher. For example, sand scatteredon icy roads keeps cars from skidding. Baseball players some-times wear textured batting gloves to increase the friction

between their hands and the bat so that the bat does notfly out of their hands.

Another way to increase friction is to increase the force pushing the surfaces together. For example, you

can ensure that your magazine will not blow away at the park by putting a heavy rock on it. The added

mass of the rock increases the friction between themagazine and the ground. Or if you are sanding a

piece of wood, you can sand the wood faster by press-ing harder on the sandpaper. Figure 17 shows another situ-

ation where friction is increased by pushing on an object.

Figure 17 No one enjoys clean-ing pans with baked-on food! To make this chore pass quickly,

press down with the scrubberto increase friction.

REVIEW

1. Explain why friction occurs.

2. Name two ways in which friction can be increased.

3. Give an example of each of the following types of fric-tion: sliding, rolling, and fluid.

4. Applying Concepts Name two ways that friction is harm-ful and two ways that friction is helpful to you when rid-ing a bicycle.

Chapter 5124

Friction and Tires

The tire shown here was used for more than 80,000 km. Whateffect did friction have on the rubber? What kind of friction ismainly responsible for the tire’s appearance? Why are car ownerswarned to change their car tires after using them for severalthousand kilometers?

NSTA

TOPIC: Force and FrictionGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP110



Gravity: A Force of AttractionIf you watch videotape of astronauts on the moon, you willnotice that when the astronauts tried to walk on the lunarsurface, they bounced around like beach balls instead.

Why did the astronauts—who were wearing heavy space-suits—bounce so easily on the moon (as shown in Figure 18),while you must exert effort to jump a few centimeters offEarth’s surface? The answer has to do with gravity. Gravity isa force of attraction between objects that is due to their masses.In this section, you will learn about gravity and the effects ithas on objects.

All Matter Is Affected by GravityAll matter has mass. Gravity is a result of mass. Therefore, allmatter experiences gravity. That is, all objects experience anattraction toward all other objects. This gravitational force“pulls” objects toward each other. Right now, because of grav-ity, you are being pulled toward this book, your pencil, andevery other object around you.

These objects are also being pulled toward you and towardeach other because of gravity. So why don’t you see the effectsof this attraction? In other words, why don’t you notice objectsmoving toward each other? The reason is that the mass ofmost objects is too small to cause an attraction large enoughto move objects toward each other. However, you are familiarwith one object that is massive enough to cause a noticeableattraction—the Earth.

Figure 18 Because gravity isless on the moon than on Earth,walking on the moon’s surfacewas a very bouncy experiencefor the Apollo astronauts.

Section

4

gravity massweight

Define gravity. State the law of universal

gravitation. Describe the difference between

mass and weight.


Scientists think seeds can “sense”gravity. The ability to sense gravity iswhat causes seeds to always sendroots down and the green shoot up.But scientists do not understand justhow seeds do this. Astronauts havegrown seedlings during space shuttlemissions to see how seeds respondto changes in gravity. So far, thereare no definite answers from theresults of these experiments.

Earth’s Gravitational Force Is Large Compared with allthe objects around you, Earth has an enormous mass. Therefore,Earth’s gravitational force is very large. You must apply forcesto overcome Earth’s gravitational force any time you lift objectsor even parts of your body.

Earth’s gravitational force pulls everything toward the cen-ter of Earth. Because of this, the books, tables, and chairs inthe room stay in place, and dropped objects fall to Earth ratherthan moving together or toward you.

The Law of Universal GravitationFor thousands of years, two very puzzling questions were “Whydo objects fall toward Earth?” and “What keeps the planets inmotion in the sky?” The two questions were treated as sepa-rate topics until a British scientist named Sir Isaac Newton(1642–1727) realized that they were two parts of the samequestion.

The Core of an Idea Legend has it that Newton made theconnection when he observed a falling apple during a sum-mer night, as shown in Figure 19. He knew that unbalancedforces are necessary to move or change the motion of objects.He concluded that there had to be an unbalanced force onthe apple to make it fall, just as there had to be an unbal-anced force on the moon to keep it moving around Earth. Herealized that these two forces are actually the same force—aforce of attraction called gravity.

A Law Is Born Newton generalized hisobservations on gravity in a law now

known as the law of universalgravitation. This law describes therelationships between gravita-

tional force, mass, and dis-tance. It is called universalbecause it applies to all objectsin the universe.

Chapter 5126

Figure 19Newton Makes the Connection

Self-CheckWhat is gravity? (Seepage 724 to check youranswer.)


The law of universal gravitation states the following: Allobjects in the universe attract each other through gravitationalforce. The size of the force depends on the masses of the objectsand the distance between them. The examples in Figure 20show the effects of the law of universal gravitation. It is easierto understand the law if you consider it in two parts.

Part 1: Gravitational Force Increases as Mass IncreasesImagine an elephant and a cat. Because an elephant has alarger mass than a cat, the amount of gravity between an el-ephant and Earth is greater than the amount of gravity betweena cat and Earth. That is why a cat is much easier to pick upthan an elephant! There is gravity between the cat and theelephant, but it is very small because the cat’s mass and theelephant’s mass are so much smaller than Earth’s mass.

The moon has less mass than Earth. Therefore, the moon’sgravitational force is less than Earth’s. Remember the astro-nauts on the moon? They bounced around as they walkedbecause they were not being pulled down with as much forceas they would have been on Earth.


Figure 20 The arrows indicatethe gravitational force betweenthe objects. The width of thearrows indicates the strength of the force.

Gravitational force is largerbetween objects withlarger masses.

If the distance between two objects is increased, thegravitational force pulling them together is reduced.

Gravitational force is smallbetween objects withsmall masses.

a

b

c


Black holes are 10 times to 1 billiontimes more massive than our sun.Thus, their gravitational force isincredibly large. The gravity of a blackhole is so large that an object thatenters a black hole can never get out.Even light cannot escape from a blackhole. Because black holes do not emit light, they cannot be seen—hencetheir name.


Part 2: Gravitational Force Decreases asDistance Increases The gravity between youand Earth is large. Whenever you jump up, youare pulled back down by Earth’s gravitationalforce. On the other hand, the sun is more than300,000 times more massive than Earth. So whydoesn’t the sun’s gravitational force affect youmore than Earth’s does? The reason is that thesun is so far away.

You are approximately 150 million kilometersaway from the sun. At this distance, the gravitybetween you and the sun is very small. If therewere some way you could stand on the sun (andnot burn up), you would find it impossible to jumpor even walk. The gravitational force acting onyou would be so great that your muscles couldnot lift any part of your body!

Although the sun’s gravitational force does nothave much of an effect on your body here, it doeshave a big effect on Earth itself and the otherplanets, as shown in Figure 21. The gravity betweenthe sun and the planets is large because the objectshave large masses. If the sun’s gravitational forcedid not have such an effect on the planets, theplanets would not stay in orbit around the sun.

Weight Is a Measure of Gravitational ForceYou have learned that gravity is a force of attraction betweenobjects that is due to their masses. Weight is a measure ofthe gravitational force exerted on an object. When you seeor hear the word weight, it usually refers to Earth’s gravi-tational force on an object. But weight can also be a measureof the gravitational force exerted on objects by the moon orother planets.

You have learned that the unitof force is a newton. Becausegravity is a force and weightis a measure of gravity,weight is also expressed innewtons (N). On Earth, a100 g object, such as amedium-sized apple, weighsapproximately 1 N.

Chapter 5128

Figure 21 Venus and Earth have approxi-mately the same mass. However, Venus iscloser to the sun. Thus, the gravity betweenVenus and the sun is greater than the gravitybetween Earth and the sun.

Venus Earth

Suppose you had a devicethat could increase ordecrease the gravitationalforce of objects around you(including small sections ofEarth). In your ScienceLog,describe what you might do with the device, what you would expect to see, and what effect the devicewould have on the weight of objects.



Weight and Mass Are Different Weight is related to mass,but the two are not the same. Weight changes when gravita-tional force changes. Mass is the amount of matter in anobject, and its value does not change. If an object is movedto a place with a greater gravitational force—like Jupiter—itsweight will increase, but its mass will remain the same. Figure 22shows the weight and mass of an object on Earth and a placewith about one-sixth the gravitational force—the moon.

Gravitational force is about the same everywhere on Earth,so the weight of any object is about the same everywhere.Because mass and weight are constant on Earth, the terms areoften used to mean the same thing. This can lead to confu-sion. Be sure you understand the difference!


REVIEW

1. How does the mass of an object relate to the gravitationalforce the object exerts on other objects?

2. How does the distance between objects affect the gravitybetween them?

3. Comparing Concepts Explain why your weight wouldchange if you orbited Earth in the space shuttle but yourmass would not.

Figure 22 The astronaut’sweight on the moon is aboutone-sixth of his weight on Earth,but his mass remains constant.

131 N

80 kg

Weight ismeasured witha spring scale.

Mass is measured witha balance.

784 N

80 kg

NSTA

TOPIC: Matter and GravityGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP115

Chapter Highlights

Chapter 5130

SECTION 1 SECTION 2

Vocabularymotion (p. 108)

speed (p. 109)

velocity (p. 110)

acceleration (p. 112)

Section Notes

• An object is in motion if itchanges position over timewhen compared with a reference point.

• The speed of a moving objectdepends on the distance trav-eled by the object and thetime taken to travel thatdistance.

• Speed and velocity are notthe same thing. Velocity isspeed in a given direction.

• Acceleration is the rate atwhich velocity changes.

• An object can accelerate bychanging speed, changingdirection, or both.

• Acceleration is calculated bysubtracting starting velocityfrom final velocity, thendividing by the time requiredto change velocity.

Labs Built for Speed (p. 646)

Detecting Acceleration (p. 647)

Vocabularyforce (p. 115)

newton (p. 115)

net force (p. 116)

Section Notes

• A force is a push or a pull.

• Forces are expressed in newtons.

• Force is always exerted byone object on another object.

• Net force is determined bycombining forces.

• Unbalanced forces pro-duce a change in motion.Balanced forces produce no change in motion.

Skills CheckMath ConceptsACCELERATION An object’s acceleration canbe determined using the following equation:

For example, suppose a cheetah running at a velocity of 27 m/s east slows down. After 15 seconds, the cheetah has stopped.

Visual UnderstandingTHE SOURCE OF FRICTION Even surfacesthat look or feel very smooth are actually roughat the microscopic level. To understand howthis roughness causes friction, review Figure 11on page 119.

THE LAW OF UNIVERSAL GRAVITATIONThis law explains that thegravity between objectsdepends on their massesand the distance between them. Review theeffects of this law by looking at Figure 20 onpage 127.

= –1.8 m/s/s east0 m/s – 27 m/s

15 s

Acceleration final velocity – starting velocitytime it takes to change velocity


SECTION 3 SECTION 4

Vocabularyfriction (p. 119)

Section Notes

• Friction is a force that opposes motion.

• Friction is caused by “hillsand valleys” touching on thesurfaces of two objects.

• The amount of frictiondepends on factors such asthe roughness of the surfacesand the force pushing thesurfaces together.

• Four kinds of friction thataffect your life are slidingfriction, rolling friction, fluidfriction, and static friction.

• Friction can be harmful orhelpful.

Labs Science Friction (p. 650)

Vocabularygravity (p. 125)

weight (p. 128)

mass (p. 129)

Section Notes

• Gravity is a force of attrac-tion between objects that isdue to their masses.

• The law of universal gravita-tion states that all objects inthe universe attract eachother through gravitationalforce. The size of the forcedepends on the masses of theobjects and the distancebetween them.

• Weight and mass are not thesame. Mass is the amount ofmatter in an object; weight is a measure of the gravita-tional force on an object.

Labs Relating Mass and Weight (p. 651)


TOPIC: Measuring Motion sciLINKS NUMBER: HSTP105

TOPIC: Forces sciLINKS NUMBER: HSTP107

TOPIC: Force and Friction sciLINKS NUMBER: HSTP110

TOPIC: Matter and Gravity sciLINKS NUMBER: HSTP115

TOPIC: The Science of Bridges sciLINKS NUMBER: HSTP125



KEYWORD: HSTMOT

131Matter in MotionCopyright © by Holt, Rinehart and Winston. All rights reserved.


To complete the following sentences, choosethe correct term from each pair of terms listedbelow:

1. ___?____ opposes motion between surfacesthat are touching. (Friction or Gravity)

2. Forces are expressed in ____?____. (newtonsor mass)

3. A _____?______ is determined by combin-ing forces. (net force or newton)

4. ___?____ is the rate at which _____?_____changes. (Velocity or Acceleration/velocity oracceleration)


Multiple Choice

5. A student riding her bicycle on a straight,flat road covers one block every 7 seconds.If each block is 100 m long, she is traveling ata. constant speed. b. constant velocity. c. 10 m/s. d. Both (a) and (b)

6. Friction is a force thata. opposes an object’s motion.b. does not exist when surfaces are very

smooth.c. decreases with larger mass.d. All of the above

7. Rolling frictiona. is usually less than sliding friction. b. makes it difficult to move objects on

wheels. c. is usually greater than sliding friction.d. is the same as fluid friction.

8. If Earth’s mass doubled, your weightwoulda. increase because gravity increases.b. decrease because gravity increases.c. increase because gravity decreases.d. not change because you are still on

Earth.

9. A forcea. is expressed in newtons. b. can cause an object to speed up, slow

down, or change direction. c. is a push or a pull.d. All of the above

10. The amount of gravity between 1 kg oflead and Earth is ______ the amount ofgravity between 1 kg of marshmallowsand Earth.a. greater than c. the same asb. less than d. none of the above

Short Answer

11. Describe the relationship between motionand a reference point.

12. How is it possible to be accelerating andtraveling at a constant speed?

13. Explain the difference between mass andweight.


Concept Mapping

14. Use the followingterms to create aconcept map: speed,velocity, acceleration,force, direction,motion.

CRITICAL THINKING ANDPROBLEM SOLVING

15. Your family is moving, and you are askedto help move some boxes. One box is soheavy that you must push it across theroom rather than lift it. What are someways you could reduce friction to makemoving the box easier?

16. Explain how using the term acceleratorwhen talking about a car’s gas pedal canlead to confusion, considering the scien-tific meaning of the word acceleration.

17. Explain why it is important for airplanepilots to know wind velocity, not justwind speed, during a flight.

MATH IN SCIENCE

18. A kangaroo hops 60 m to the east in 5 seconds.a. What is the kangaroo’s speed? b. What is the kangaroo’s velocity? c. The kangaroo stops at a lake for a drink

of water, then starts hopping again tothe south. Every second, the kangaroo’svelocity increases 2.5 m/s. What is thekangaroo’s acceleration after 5 seconds?


19. Is this a graph of positive or negativeacceleration? How can you tell?

20. You know how to combine two forcesthat act in one or two directions. Thesame method you learned can be used tocombine several forces acting in severaldirections. Examine the diagrams below,and predict with how much force and inwhat direction the object will move.

Velo

city

(m

/s)

Time (seconds)


12 N9 N

3 N

3 N

5 N5 N

5 N

4 N

6 N

6 N

a

b

c



ReadingCheck-up


134

Is It Real . . . or Is It Virtual?

You stand in the center of a darkenedroom and put on a helmet. The helmetcovers your head and face, making it

impossible for you to see or hear anything fromoutside. Wires run from the helmet to a seriesof computers, carrying information about howyour head is positioned and where you arelooking. Other wires carry back to you thesights and sounds the computer wants you to“see” and “hear.” All of a sudden you find your-self driving a race car around a tricky course at 300 km/h. Then in another instant, you arein the middle of a rain forest staring at a live snake!

It’s All an IllusionSuch simulated-reality experiences were oncethought the stuff of science fiction alone. Buttoday devices called motion simulators canstimulate the senses of sight and sound to create illusions of movement.

Virtual-reality devices, as these motion simu-lators are called, were first used during WorldWar II to train pilots. Mock-ups of fighter-planecockpits, films of simulated terrain, and a joy-stick that manipulated large hydraulic arms simulated the plane in “virtual flight.” Today’s jet pilots train with similar equipment, exceptthe simulators use extremely sophisticatedcomputer graphics instead of films.

Fooled You!Virtual-reality hoods and gloves take peopleinto a variety of “realities.” Inside the hood, twosmall television cameras or computer-graphicimages fool the wearer’s sense of vision. Thebrain perceives the image as three-dimensionalbecause one image is placed in front of eacheye. As the images change, the computeradjusts the scene’s perspective so that itappears to the viewer as though he or she is

moving through the scene. When the positionof the head changes, the computer adjusts thescene to account for the movement. All thewhile, sounds coming through the headphonestrick the wearer’s ears into thinking he or she ismoving too.

In addition to hoods, gloves, and images,virtual-reality devices may have other types of sensors. Driving simulators, for instance,often have a steering wheel, a gas pedal, and abrake so that the participant has the sensationof driving. So whether you want spine-tinglingexcitement or on-the-job training, virtual realitycould very well take you places!

Explore New Realities What other activities or skills could belearned or practiced with virtual reality? Whatare some problems with relying on this tech-nology? Record your ideas in your ScienceLog.

Wearing a virtual-reality helmet helps tolessen the pain this burn patient feels whilehis dressings are changed.


P H Y S I C A L S C I E N C E • E A R T H S C I E N C E

The Golden Gate Bridge

135

Have you ever relaxed in a hammock? If so, youmay have noticed how tense the strings gotwhen the hammock supported your weight.Now imagine a hammock 1,965 m long sup-porting a 20-ton roadway with more than100,000 cars traveling along its length eachday. That describes the Golden Gate Bridge!Because of the way the bridge is built, it is very much like a giant hammock.

Tug of WarThe bridge’s roadway is suspended from maincables 2.33 km long that sweep from one endof the bridge to the other and that areanchored at each end. Smaller cables calledhangers connect the main cables to the road-way. Tension, the force of being pulled apart, iscreated as the cables are pulled down by theweight of the roadway while being pulled up bytheir attachment to the top of each tower.

Towering AboveTowers 227 m tall support the cables over thelong distance across San Francisco Bay, makingthe Golden Gate the tallest bridge in the world.The towers receive a force that is the exactopposite of tension—compression. Compression

is the force of being pushed together. The maincables holding the weight of the roadway pushdown on the top of the towers while Earthpushes up on the bottom.

Stretching the LimitsTension and compression are elastic forces,which means they are dependent on elasticity,the ability of an object to return to its originalshape after being stretched or compressed. Ifan object is not very elastic, it breaks easily orbecomes permanently deformed when sub-jected to an elastic force. The cables and tow-ers of the Golden Gate Bridge are made ofsteel, a material with great elastic strength. Asingle steel wire 2.54 mm thick can supportover half a ton without breaking!

On the RoadThe roadway of the Golden Gate Bridge issubjected to multiple forces at the same time,including friction, gravity, and elastic forces.Rolling friction is caused by the wheels of eachvehicle moving across the roadway’s surface.Gravity pulls down on the roadway but is coun-teracted by the support of the towers and cables.This causes each roadway span to bend slightlyand experience both tension and compression.The bottom of each span is under tensionbecause the cables and towers pull up along theroad’s sides, while gravity pulls down at its cen-ter. These same forces cause compression of thetop of each span. Did you ever imagine that somany forces were at work on a bridge?

Bridge the Gap Find out more about another type of bridge,such as an arch, a beam, or a cable-stayedbridge. How do forces such as friction, gravity,tension, and compression affect these types ofbridges?

The Golden Gate Bridge spans the SanFrancisco Bay.


136 Chapter 6

Gravity and Motion . . 138MathBreak . . . . . . . . . 139QuickLab . . . . . . . . . . 144Internet Connect . . . . 144

Newton’s Laws of Motion . . . . . . . . . . 145

Apply . . . . . . . . . . . . . 146QuickLab . . . . . . . . . . 147Environment

Connection . . . . . . . 148MathBreak . . . . . . . . . 149Internet Connect . . . . 149

Chapter Review . . . . . . . . . 156


LabBook . . . . . . . . . . . 652–657

Forcesin MotionForcesin Motion

Vomit CometHave you ever wondered what it would be like to movearound without gravity? To help train astronauts for spaceflight, scientists have designed a special airplane called the KC-135 that simulates what it feels like to move withreduced gravity. The KC-135 first flies upward at a steepangle. When the airplane flies downward at a 45° angle, the effect of reduced gravity is produced inside. Then, theastronaut trainees in the plane can “float.” Because the floating often makes passengers queasy, the KC-135 has earned a nickname—the Vomit Comet. In this chapter, you will learn how gravity affects the motion of objects and how the laws of motion apply to your life.


1. How does the force of grav-ity affect falling objects?

2. What is projectile motion?3. What are Newton’s laws of

motion?4. What is momentum?


Forces in Motion 137

FALLING WATER Gravity is one of the most importantforces in your life. In this activity,you will observe the effect of gravityon a falling object.

Procedure

1. Place a wide plastic tub on thefloor. Punch a small hole in theside of a paper cup, near the bottom.

2. Hold your finger over the hole, andfill the cup with water. Keepingyour finger over the hole, hold the cup about waist high abovethe tub.

3. Uncover the hole. Describe yourobservations in your ScienceLog.

4. Next, predict what will happen tothe water if you drop the cup atthe same time you uncover thehole. Write your prediction in yourScienceLog.

5. Cover the hole with your fingeragain, and refill the cup.

6. Uncover the hole, and drop thecup at the same time. Record your observations.

7. Clean up any spilled water withpaper towels.

Analysis

8. What differences did you observein the behavior of the water duringthe two trials?

9. In the second trial, how fast did thecup fall compared with the water?



Chapter 6138

Gravity and MotionSuppose you drop a baseball and a marble at the same timefrom the same height. Which do you think would land first?In ancient Greece around 400 B.C., an important philosophernamed Aristotle (ER is TAWT uhl) believed that the rate at whichan object falls depends on the object’s mass. Imagine that youcould ask Aristotle which object would land first. He wouldpredict that the baseball would land first.

All Objects Fall with theSame AccelerationIn the late 1500s, a young Italian scientist named Galileo ques-tioned Aristotle’s idea about falling objects. Galileo proved thatthe mass of an object does not affect the rate at which it falls.According to one story, Galileo did this by dropping two can-nonballs of different masses from the top of the Leaning Towerof Pisa. The crowd watching from the ground was amazed to

see the two cannonballs land at the same time.Whether or not this story is true, Galileo’s ideachanged people’s understanding of gravity andfalling objects.

Acceleration Due to Gravity Objects fall tothe ground at the same rate because the accel-eration due to gravity is the same for all objects.Does that seem odd? The force of gravity isgreater between Earth and an object with a largemass than between Earth and a less massiveobject, so you may think that the accelerationdue to gravity should be greater too. But agreater force must be applied to a large massthan to a small mass to produce the same accel-eration. Thus, the difference in force is can-celed by the difference in mass. Figure 1 showsobjects with different masses falling with thesame acceleration.

Figure 1 A table tennis ball and a golf ball fallwith the same acceleration even though theyhave different masses.

Section

1

terminal velocityfree fallprojectile motion

Explain how gravity and air resis-tance affect the acceleration offalling objects.

Explain why objects in orbitappear to be weightless.

Describe how an orbit is formed. Describe projectile motion.


Accelerating at a Constant Rate All objects accelerate towardEarth at a rate of 9.8 meters per second per second, which isexpressed as 9.8 m/s/s. This means that for every second thatan object falls, the object’s downward velocity increases by 9.8 m/s, as shown in Figure 2. Remember, this acceleration is thesame for all objects regardless of their mass. Do the MathBreakat right to learn how to calculate the velocity of a falling object.

Air Resistance Slows Down AccelerationTry this simple experiment. Drop two sheets of paper—onecrumpled in a tight ball and the other kept flat. Did yourresults contradict what you just learned about falling objects?The flat paper fell more slowly because of fluid friction thatopposes the motion of objects through air. This fluid frictionis also known as air resistance. Air resistance occurs betweenthe surface of the falling object and the air that surrounds it.


v = 0 m/s downward

v = 9.8 m/s downward



Velocity of Falling ObjectsTo find the change in velocity(v) of a falling object, multi-ply the acceleration due togravity (g) by the time ittakes for the object to fall inseconds (t):

v g t

For example, a stone atrest is dropped from a cliff,and it takes 3 seconds to hitthe ground. Its downwardvelocity when it hits theground is as follows:

v 9.8 ms/s 3 s

29.4 m/s

Now It’s Your TurnA penny at rest is droppedfrom the top of a tall stairwell.

1. What is the penny’s veloc-ity after it has fallen for 2 seconds?

2. The penny hits the groundin 4.5 seconds. What is itsfinal velocity?

MATH BREAK

Gravity helps make roller coastersthrilling to ride. Readabout a roller coaster

designer on page159.

Figure 2 A falling object acceleratesat a constant rate. Each second, theobject falls faster and farther than itdid the second before.

1st s4.9 m

2nd s14.7 m

3rd s24.5 m


Air Resistance Affects Some Objects More than OthersThe amount of air resistance acting on an object depends onthe size and shape of the object. Air resistance affects the flatsheet of paper more than the crumpled one, causing the flatsheet to fall more slowly than the crumpled one. Because airis all around you, any falling object you see is affected by airresistance. Figure 3 shows the effect of air resistance on thedownward acceleration of a falling object.

Acceleration Stops at the Terminal VelocityAs long as the net force on a falling object

is not zero, the object accelerates downward.But the amount of air resistance on an

object increases as the speed of the objectincreases. As an object falls, the upward force

of air resistance continues to increase until itexactly matches the downward force of gravity.

When this happens, the net force is zero, and theobject stops accelerating. The object then falls at a con-

stant velocity, which is called the terminal velocity.Sometimes the fact that falling objects have a terminal

velocity is a good thing. The terminal velocity of hailstones isbetween 5 and 40 m/s, depending on the size of the stones.Every year cars, buildings, and vegetation are all severely dam-aged in hail storms. Imagine how much more destructive hailwould be if there were no air resistance—hailstones would hitthe Earth at velocities near 350 m/s! Figure 4 shows anothersituation in which terminal velocity is helpful.

140

Figure 3 The force of gravity pullsthe object downward as the forceof air resistance pushes it upward.

Self-CheckWhich is more affectedby air resistance—aleaf or an acorn? (Seepage 724 to check youranswer.)

Figure 4The parachuteincreases the airresistance of thissky diver, slowinghim to a safe terminal velocity.

Chapter 6

This arrow represents the force of airresistance pushing up on the object.This force is subtracted from the forceof gravity to produce the net force.

This arrow represents the net forceon the object. Because the net forceis not zero, the object still acceler-ates downward, but not as fast as itwould without air resistance.

This arrow represents the force of gravityon the object. If this were the only forceacting on the object, it would accelerateat a rate of 9.8 m/s/s.


Free Fall Occurs When There IsNo Air Resistance Sky divers areoften described as being in free fallbefore they open their parachutes.However, that is an incorrect descrip-tion, because air resistance is alwaysacting on the sky diver.

An object is in free fall only ifgravity is pulling it down and noother forces are acting on it. Becauseair resistance is a force (fluid fric-tion), free fall can occur only wherethere is no air—in a vacuum (a placein which there is no matter) or inspace. Figure 5 shows objects fallingin a vacuum. Because there is no air resistance, the two objects are in free fall.

Orbiting Objects Are in Free FallLook at the astronaut in Figure 6. Why is theastronaut floating inside the space shuttle? It mightbe tempting to say it is because she is “weightless”in space. In fact, you may have read or heard thatobjects are weightless in space. However, it is impos-sible to be weightless anywhere in the universe.

Weight is a measure of gravitationalforce. The size of the force depends on themasses of objects and the distancesbetween them. If you traveled in space faraway from all the stars and planets, thegravitational force acting on you would bealmost undetectable because the distancebetween you and other objects would begreat. But you would still have mass, andso would all the other objects in the uni-verse. Therefore, gravity would still attractyou to other objects—even if just slightly—so you would still have weight.

Astronauts “float” in orbiting space-ships because of free fall. To understandthis better, you need to understand whatorbiting means and then consider theastronauts inside the ship.


Figure 5 Air resistancenormally causes afeather to fall moreslowly than an apple.But in a vacuum, thefeather and the applefall with the same accel-eration because bothare in free fall.

Figure 6 Astronauts appear to be weightless while floatinginside the space shuttle—butthey’re not!


Two Motions Combine to Cause Orbiting An object is saidto be orbiting when it is traveling in a circular or nearly cir-cular path around another object. When a spaceship orbitsEarth, it is moving forward, but it is also in free fall towardEarth. Figure 7 shows how these two motions occur togetherto cause orbiting.

As you can see in the illustration above, the space shut-tle is always falling while it is in orbit. So why don’t astro-nauts hit their heads on the ceiling of the falling shuttle?Because they are also in free fall—they are always falling, too.Because the astronaut in Figure 6 is in free fall, she appearsto be floating.

The Role of Gravity in Orbiting Besides spaceships and satel-lites, many other objects in the universe are in orbit. Themoon orbits the Earth, Earth and the other planets orbit thesun, and many stars orbit large masses in the center of galax-ies. All of these objects are traveling in a circular or nearly cir-cular path. Remember, any object in circular motion isconstantly changing direction. Because an unbalanced force isnecessary to change the motion of any object, there must bean unbalanced force working on any object in circular motion.

The unbalanced force that causes objects to move in a cir-cular path is called a centripetal force. Gravity provides the cen-tripetal force that keeps objects in orbit. The word centripetalmeans “toward the center.” As you can see in Figure 8, thecentripetal force on the moon points toward the center of thecircle traced by the moon’s orbit.

Chapter 6142

Figure 7 How an Orbit Is Formed

Path of moon

Centripetal force on the moon

Figure 8 The moon stays in orbitaround the Earth because Earth’sgravitational force provides a centripetal force on the moon.

The shuttle is in free fallbecause gravity pulls itdown toward Earth. Thiswould be its path if itwere not traveling forward.

b

The actual path of theshuttle follows the curveof Earth’s surface. This isknown as orbiting.

c

The shuttle moves forward at a constant speed.This would be its path if there were no gravity.

a


Projectile Motion and GravityThe orbit of the space shuttle around the Earth is an exam-ple of projectile (proh JEK tuhl) motion. Projectile motion isthe curved path an object follows when thrown or propellednear the surface of the Earth. The motions of leaping dancers,thrown balls, hopping grasshoppers, and arrows shot from abow are all examples of projectile motion. Projectile motionhas two components—horizontal and vertical. The two com-ponents are independent; that is, they have no effect on eachother. When the two motions are combined, they form a curvedpath, as shown in Figure 9.

Horizontal Motion When you throw a ball, your hand exertsa force on the ball that makes the ball move forward. Thisforce gives the ball its horizontal motion. Horizontal motionis motion that is parallel to the ground.

After you let go of the ball, there are no horizontal forcesacting on the ball (if you ignore air resistance). Therefore, thereare no forces to change the ball’s horizontal motion. Thus, thehorizontal velocity of the ball is constant after the ball leavesyour hand, as shown in Figure 9.


A football being passed

Balls being juggled

An athlete doing a high jump

Water sprayed by a sprinkler

A swimmer diving into water

A leaping frog

Examples of Objects in Projectile Motion

The ball’s verticalvelocity increasesbecause gravitycauses it to accel-erate downward.

The two motionscombine to forma curved path.

After the ball leaves the pitcher’s hand,its horizontal velocity is constant.

a

b

c

Figure 9 Two motions combine to form projectile motion.


Vertical Motion After you throw a ball, gravity pulls itdownward, giving the ball vertical motion. Vertical motionis motion that is perpendicular to the ground. Because objectsin projectile motion accelerate downward, you always have toaim above a target if you want to hit it with a thrown or pro-pelled object. That’s why when you aim an arrow directly ata bull’s-eye, your arrow strikes the bottom of the target ratherthan the middle.

Gravity pulls objects in projectile motion down with anacceleration of 9.8 m/s/s (if air resistance is ignored), just as itdoes all falling objects. Figure 10 shows that the downwardacceleration of a thrown object and a falling object are the same.

Chapter 6144

1. How does air resistance affect the acceleration of fallingobjects?

2. Explain why an astronaut in an orbiting spaceship floats.

3. How is an orbit formed?

4. Applying Concepts Think about a sport you play thatinvolves a ball. Identify at least four different instancesin which an object is in projectile motion.

REVIEW

Figure 10 Projectile Motion and Acceleration Due to Gravity

The yellow ball wasgiven a horizontal pushoff the ledge and followsprojectile motion.

The balls have thesame accelerationdue to gravity. Thehorizontal motionof the yellow balldoes not affect itsvertical motion.

The red ballwas droppedwithout a horizontal push.

Penny Projectile Motion

1. Position a flat rulerand two pennies ona desk or table asshown below.

2. Hold the ruler by the endthat is on the desk. Movethe ruler quickly in thedirection shown so thatthe ruler knocks the pennyoff the table and so thatthe other penny alsodrops. Repeat severaltimes.

3. Which penny travels withprojectile motion? In whatorder do the pennies hitthe ground? Record andexplain your answers inyour ScienceLog.

NSTA

TOPIC: The Force of Gravity, Projectile Motion

GO TO: www.scilinks.orgsciLINKS NUMBER: HSTP130, HSTP140



Newton’s Laws of MotionIn 1686, Sir Isaac Newton published his book Principia. In it,he described three laws that relate forces to the motion ofobjects. Although he did not discover all three of the laws, heexplained them in a way that helped many people understandthem. Thus, the three laws are commonly known as Newton’slaws of motion. In this section, you will learn about these lawsand how they influence the motion of objects.

Newton’s First Law of Motion

An object at rest remains at rest and an object in motion remains in motion at constant speed and in astraight line unless acted on by an unbalanced force.

Newton’s first law of motion describes the motion of an object that has a net force of zero acting on it. This lawmay seem complicated when you first read it, but it’s easy tounderstand when you consider its two parts separately.

Part 1: Objects at Rest What does it mean for an objectto be at rest? Objects don’t get tired! An object that is notmoving is said to be at rest. Objects are at rest all around you.A plane parked on a runway, a chair on the floor, and a golfball balanced on a tee are all examples of objects at rest.

Newton’s first law says that objects at rest will remain atrest unless they are acted on by an unbalanced force. Thatmeans that objects will not start moving until a push or a pullis exerted on them. A plane won’t soar in the air unless it ispushed by the exhaust from its jet engines, a chair won’t slideacross the room unless you push it, and a golf ball won’t moveoff the tee unless struck by a golf club, as shown in Figure 11.

Figure 11 A golf ball willremain at rest on a tee until it is acted on by the unbalancedforce of a moving club.

Unbalanced force

Object in motion

Object at rest

Section

2

inertia momentum

State and apply Newton’s lawsof motion.

Compare the momentum of different objects.

State and apply the law of conservation of momentum.


Stopping Motion

The dummy in this crash test is wearing a seat belt, but the car does not have anair bag. Explain why Newton’s first law ofmotion could lead to serious injuries inaccidents involving cars without air bags.

Part 2: Objects in MotionThink about riding in a bumpercar at an amusement park. Yourride is pleasant as long as youare driving in an open space. Butthe name of the game is bumpercars, so sooner or later you arelikely to run into another car,as shown in Figure 12.

The second part of Newton’sfirst law explains that an objectmoving at a certain velocity willcontinue to move forever at thesame speed and in the samedirection unless some unbal-anced force acts on it. Thus,your bumper car stops, but youcontinue to move forward untilyour seat belt stops you.

Friction and Newton’s First Law Because an object inmotion will stay in motion forever unless it is acted on by anunbalanced force, you should be able to give your desk a smallpush and send it sailing across the floor. If you try it, you willfind that the desk quickly comes to a stop. What does thistell you?

There must be an unbalanced force that acts on the deskto stop its motion. That unbalanced force is friction. The fric-tion between the desk and the floor works against the motionof the desk. Because of friction, it is often difficult to observethe effects of Newton’s first law on the motion of everydayobjects. For example, friction will cause a ball rolling on grassto slow down and stop. Friction will also make a car deceler-ate on a flat surface if the driver lets up on the gas pedal.Because of friction, the motion of these objects changes.

Chapter 6146

Another unbalancedforce, from your seat belt, changesyour motion.

The collision changes your car’smotion, but not yours. Your motioncontinues with the same velocity.

b

c

An unbalanced forcefrom another caracts on your car,changing its motion.

a

Figure 12 Bumper cars letyou have fun with Newton’sfirst law.


Inertia Is Related to Mass Newton’s first law of motion issometimes called the law of inertia. Inertia (in UHR shuh) isthe tendency of all objects to resist any change in motion.Due to inertia, an object at rest will remain at rest until some-thing makes it move. Likewise, inertia is why a moving objectstays in motion with the same velocity unless a force acts onit to change its speed or direction. Inertia causes you to slidetoward the side of a car when the driver makes a sharp turn.Inertia is also why it is impossible for a plane, car, or bicycleto stop instantaneously.

Mass Is a Measure of Inertia An object with a small masshas less inertia than an object with a large mass. Therefore, itis easier to start and to change the motion of an object witha small mass. For example, a softball has less mass and there-fore less inertia than a bowling ball. Because the softball hasa small amount of inertia, it is easy to pitch a softball and tochange its motion by hitting it with a bat. Imagine how dif-ficult it would be to play softball with a bowling ball! Figure 13further illustrates the relationship between mass and inertia.Try the QuickLab at right to test the relationship yourself.


Figure 13 Inertia makes it harder to push a car thanto push a bicycle. Inertia also makes it easier to stop amoving bicycle than a car moving at the same speed.

Self-CheckWhen you stand while riding a bus, why do you tendto fall backward when the bus starts moving? (See page 724 to check your answer.)

First-Law Magic

1. On a table or desk,place a large, emptyplastic cup on topof a paper towel.

2. Without touching the cupor tipping it over, removethe paper towel fromunder the cup. What didyou do to accomplish this?

3. Repeat the first two stepsa few times until you arecomfortable with the procedure.

4. Fill the cup half full withwater, and place the cupon the paper towel.

5. Once again, remove thepaper towel from underthe cup. Was it easier orharder to do this? Explainyour answer in terms ofmass and inertia.


Newton’s Second Law of Motion

The acceleration of an object depends on the mass of the object and the amount of force applied.

Newton’s second law describes the motion of an object whenan unbalanced force is acting on it. As with Newton’s first law,it is easier to consider the parts of this law separately.

Part 1: Acceleration Depends on Mass Suppose you arepushing a shopping cart at the grocery store. At the beginningof your shopping trip, you have to exert only a small forceon the cart to accelerate it. But when the cart is full, the sameamount of force will not accelerate the cart as much as before,as shown in Figure 14. This example illustrates that for thesame force, an object’s acceleration decreases as its mass increasesand its acceleration increases as its mass decreases.

Part 2: Acceleration Depends on Force Now suppose yougive the shopping cart a hard push, as shown in Figure 15.The cart will start moving faster than if you only gave it asoft push. This illustrates that an object’s acceleration increasesas the force on it increases. Conversely, an object’s accelerationdecreases as the force on it decreases.

The acceleration of an object is always in the same direc-tion as the force applied. The shopping cart moved forwardbecause the push was in the forward direction. To changethe direction of an object, you must exert a force in the direc-tion you want the object to go.

Chapter 6148

Figure 14 If the force applied isthe same, the acceleration of theempty cart is greater than theacceleration of the full cart.

Figure 15 Acceleration willincrease when a larger force is exerted.

Modern cars pollute the air less thanolder cars. One reason for this is thatmodern cars are less massive thanolder models and have considerablysmaller engines. According toNewton’s second law, a less massiveobject requires less force to achievethe same acceleration as a moremassive object. This is why a smallercar can have a smaller engine andstill have acceptable acceleration.And because smaller engines useless fuel, they pollute less.



Expressing Newton’s Second Law Mathematically Therelationship of acceleration (a) to mass (m) and force (F) canbe expressed mathematically with the following equation:

a mF

This equation is often rearranged to the following form:

F m a

Both forms of the equation can be used to solve problems. Trythe MathBreak at right to practice using the equations.Newton’s second law explains why objects fall to Earth withthe same acceleration. In Figure 16, you can see how the largerweight of the watermelon is offset by its greater inertia. Thus,the accelerations of the watermelon and the apple are the samewhen you put the numbers into the equation for acceleration.


1. How is inertia related to Newton’s first law of motion?

2. Name two ways to increase the acceleration of an object.

3. Making Predictions If the acceleration due to gravitywere somehow doubled to 19.6 m/s/s, what would happen to your weight?

Figure 16 Newton’s Second Law and Acceleration Due to Gravity

The apple has less mass, sothe gravitational force on it issmaller. However, the applealso has less inertia and iseasier to move.

The watermelon has moremass and therefore more iner-tia, so it is harder to move.

m 1.02 kg

F 10 NF 1 N

1 N 1 kg•m/s/s

10 N 10 kg•m/s/s

Second-Law ProblemsYou can rearrange theequation F m a to findacceleration and mass asshown below.

a mF m a

F

1. What is the acceleration ofa 7 kg mass if a force of68.6 N is used to move ittoward Earth? (Hint: 1 N isequal to 1 kg•m/s/s.)

2. What force is necessary toaccelerate a 1,250 kg carat a rate of 40 m/s/s?

3. What is the mass of anobject if a force of 34 Nproduces an accelerationof 4 m/s/s?

MATH BREAK

REVIEW

a 1

0k.g1•0

m2

/ksg/s

9.8 m/s/s a 10

1k.0g•2mk/gs/s

9.8 m/s/s

m 0.102 kg

NSTA

TOPIC: Newton’s Laws of MotionGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP145


Newton’s Third Law of Motion

Whenever one object exerts a force on a second object, the second object exerts an equal and

opposite force on the first.

Newton’s third law can be simply stated as follows: Allforces act in pairs. If a force is exerted, another force occursthat is equal in size and opposite in direction. The law itselfaddresses only forces. But the way that force pairs interactaffects the motion of objects.

What is meant by “forces act in pairs”? Study Figure 17 tolearn how one force pair helps propel a swimmer throughwater.

Action and reaction force pairs occur even when there isno motion. For example, you exert a force on a chair whenyou sit on it. Your weight pushing down on the chair is theaction force. The reaction force is the force exerted by thechair that pushes up on your body and is equal to your weight.

Force Pairs Do Not Act on the Same Object You knowthat a force is always exerted by one object on another object.This is true for all forces, including action and reaction forces.However, it is important to remember that action and reac-tion forces in a pair do not act on the same object. If theydid, the net force would always be zero and nothing wouldever move! To understand this better, look back at Figure 17.In this example, the action force was exerted on the water bythe swimmer’s hands and feet. But the reaction force wasexerted on the swimmer’s hands and feet by the water. Theforces did not act on the same object.

Chapter 6150

The action force isthe swimmer’s handsand feet pushing onthe water.

The reaction force is the water push-ing on the hands and feet. The reac-tion force moves the swimmer forward.

Figure 17 The action force andreaction force are a pair. The twoforces are equal in size butopposite in direction.

Choose a sport that youenjoy playing or watching. Inyour ScienceLog, list five waysthat Newton’s laws of motionare involved in the game youselected.


The Effect of a Reaction Can Be Difficult to See Anotherexample of a force pair is shown in Figure 18. Remember, grav-ity is a force of attraction between objects that is due to theirmasses. If you drop a ball off a ledge, the force of gravity pullsthe ball toward Earth. This is the action force exerted by Earthon the ball. But the force of gravity also pulls Earth towardthe ball. That is the reaction force exerted by the ball on Earth.

It’s easy to see the effect of the action force—the ball fallsto Earth. Why don’t you notice the effect of the reaction force—Earth being pulled upward? To find the answer to this ques-tion, think back to Newton’s second law. It states that theacceleration of an object depends on the force applied to itand on the mass of the object. The force on Earth is equal tothe force on the ball, but the mass of Earth is much largerthan the mass of the ball. Therefore, the acceleration of Earthis much smaller than the acceleration of the ball. The accel-eration is so small that you can’t even see it or feel it. Thus,it is difficult to observe the effect of Newton’s third law onfalling objects.

More Examples of Action and Reaction Force Pairs Theexamples below illustrate a variety of action and reaction forcepairs. In each example, notice which object exerts the actionforce and which object exerts the reaction force.


Figure 18 The force of gravitybetween Earth and a fallingobject is a force pair.

Action force

Reaction force

The rabbit’s legs exert a force onEarth. Earth exerts an equal forceon the rabbit’s legs, causing therabbit to accelerate upward.

The bat exerts a forceon the ball, sendingthe ball into the out-field. The ball exerts anequal force on the bat,but the bat does notfly toward the catcherbecause the batter isexerting another forceon the bat.

The shuttle’s thrusterspush the exhaust gasesdownward as the gasespush the shuttle upwardwith an equal force.

When you hit a table withyour hand, your hand willhurt. This is because thetable meets your handwith a force equal in sizeto the force you exerted.


Momentum Is a Property of Moving ObjectsIf a compact car and a large truck are traveling with the samevelocity, it takes longer for the truck to stop than it does forthe car if the same braking force is applied. Likewise, it takeslonger for a fast moving car to stop than it does for a slowmoving car with the same mass. The truck and the fast mov-ing car have more momentum than the compact car and theslow moving car.

Momentum is a property of a moving object that dependson the object’s mass and velocity. The more momentum anobject has, the harder it is to stop the object or change itsdirection. Although the compact car and the truck are travel-ing with the same velocity, the truck has more mass and there-fore more momentum, so it is harder to stop than the car.Similarly, the fast moving car has a greater velocity and thusmore momentum than the slow moving car.

Momentum Is Conserved When a moving object hitsanother object, some or all of the momentum of the firstobject is transferred to the other object. If only some of themomentum is transferred, the rest of the momentum stayswith the first object.

Imagine you hit a billiard ball with a cue ball so that thebilliard ball starts moving and the cue ball stops, as shown inFigure 19. The cue ball had a certain amount of momentumbefore the collision. During the collision, all of the cue ball’smomentum was transferred to the billiard ball. After the col-lision, the billiard ball moved away with the same amount ofmomentum the cue ball had. This example illustrates the lawof conservation of momentum. Any time two or more objectsinteract, they may exchange momentum, but the total amountof momentum stays the same.

Chapter 6152

Jumping beans appear toleap into the air with noforces acting on them.However, inside each beanis a small insect larva. Whenthe larva moves suddenly, itapplies a force to the shellof the bean. The momentumof the larva is transferred tothe bean, and the bean“jumps.”

Momentum

Momentum

Figure 19 The momentumbefore a collision is equal to themomentum after the collision.



Figure 20 The action forcemakes the billiard ball beginmoving, and the reaction forcestops the cue ball’s motion.

1. Name three action and reaction force pairs involved indoing your homework. Name what object is exerting andwhat object is receiving the forces.

2. Which has more momentum, a mouse running at 1 m/snorth or an elephant walking at 3 m/s east? Explain youranswer.

3. Applying Concepts When a truck pulls a trailer, the trailerand truck accelerate forward even though the action andreaction forces are the same size but in opposite direc-tions. Why don’t these forces balance each other out?

REVIEW

Catapult forward! Or is it backward? Find out on

page 656 of the LabBook.

Bowling is another example of how conservationof momentum is used in a game. The bowling ballrolls down the lane with a certain amount ofmomentum. When the ball hits the pins, some ofthe ball’s momentum is transferred to the pins and the pins move off in different directions.Furthermore, some of the pins that were hit by theball go on to hit other pins, transferring the momen-tum again.

Conservation of Momentum and Newton’s Third LawConservation of momentum can be explained by Newton’s thirdlaw. In the example with the billiard ball, the cue ball hit thebilliard ball with a certain amount of force. This was the actionforce. The reaction force was the equal but opposite force exertedby the billiard ball on the cue ball. The action force made thebilliard ball start moving, and the reaction force made the cueball stop moving, as shown in Figure 20. Because the action andreaction forces are equal and opposite, momentum is conserved.

Reaction forceAction force

Chapter Highlights

Chapter 6154

SECTION 1

Vocabularyterminal velocity (p. 140)

free fall (p. 141)

projectile motion (p. 143)

Section Notes

• All objects accelerate towardEarth at 9.8 m/s/s.

• Air resistance slows the accel-eration of falling objects.

• An object is in free fall ifgravity is the only force

acting on it.

• An orbit is formedby combining forward

motion and free fall.

• Objects in orbit appearto be weightless because

they are in free fall.

• A centripetal force is neededto keep objects in circularmotion. Gravity acts as acentripetal force to keepobjects in orbit.

• Projectile motion is thecurved path an object followswhen thrown or propellednear the surface of Earth.

• Projectile motion has twocomponents—horizontal andvertical. Gravity affects onlythe vertical motion of projec-tile motion.

LabsA Marshmallow Catapult(p. 652)

Skills CheckMath ConceptsNEWTON’S SECOND LAW The equation a = F/ m on page 149 summarizes Newton’s sec-ond law of motion. The equation shows the rela-tionship between the acceleration of an object,the force causing the acceleration, and theobject’s mass. For example, if you apply a force of18 N to a 6 kg object, the object’s acceleration is

a mF

168kNg

18 k

6g •

kmg

/s/s 3 m/s/s

Visual UnderstandingHOW AN ORBIT IS FORMED An orbit is acombination of two motions—forward motionand free fall. Figure 7 on page 142 shows howthe two motions combine to form an orbit.


SECTION 2

Vocabularyinertia (p. 147)

momentum (p. 152)

Section Notes

• Newton’s first law of motionstates that the motion of anobject will not change if nounbalanced forces act on it.

• Inertia is the tendency ofmatter to resist a change inmotion. Mass is a measure ofinertia.

• Newton’s second law ofmotion states that the accel-eration of an object dependson its mass and on the forceexerted on it.

• Newton’s third law ofmotion states that wheneverone object exerts a force on asecond object, the secondobject exerts an equal andopposite force on the first.

• Momentum is the propertyof a moving object thatdepends on its mass andvelocity.

• When two or more objectsinteract, momentum may beexchanged, but the totalamount of momentum doesnot change. This is the law ofconservation of momentum.

LabsBlast Off! (p. 653)

Inertia-Rama! (p. 654)

Quite a Reaction (p. 656)


TOPIC: The Force of Gravity sciLINKS NUMBER: HSTP130

TOPIC: Gravity and Orbiting Objects sciLINKS NUMBER: HSTP135

TOPIC: Projectile Motion sciLINKS NUMBER: HSTP140

TOPIC: Newton’s Laws of Motion sciLINKS NUMBER: HSTP145



KEYWORD: HSTFOR

155Forces in MotionCopyright © by Holt, Rinehart and Winston. All rights reserved.

USING VOCABULARY


1. An object in motion tends to stay inmotion because it has ___?____. (inertia orterminal velocity)

2. Falling objects stop accelerating at___?____. (free fall or terminal velocity)

3. ___?____ is the path that a thrown objectfollows. (Free fall or Projectile motion)

4. A property of moving objects thatdepends on mass and velocity is ___?____.(inertia or momentum)

5. ___?____ only occurs when there is no airresistance. (Momentum or Free fall)


Multiple Choice

6. A feather and a rock dropped at the sametime from the same height would land atthe same time when dropped bya. Galileo in Italy.b. Newton in England.c. an astronaut on the moon.d. an astronaut on the space shuttle.

7. When a soccer ball is kicked, the actionand reaction forces do not cancel eachother out becausea. the force of the foot on the ball is

bigger than the force of the ball on the foot.

b. the forces act on two different objects.c. the forces act at different times.d. All of the above

8. An object is inprojectile motion ifa. it is thrown with a horizontal push.b. it is accelerated downward by gravity.c. it does not accelerate horizontally.d. All of the above

9. Newton’s first law of motion appliesa. to moving objects.b. to objects that are not moving.c. to objects that are accelerating.d. Both (a) and (b)

10. Acceleration of an objecta. decreases as the mass of the object

increases.b. increases as the force on the object

increases.c. is in the same direction as the force on

the object.d. All of the above

11. A golf ball and a bowling ball are movingat the same velocity. Which has moremomentum?a. the golf ball, because it has less massb. the bowling ball, because it has more

massc. They both have the same momentum

because they have the same velocity.d. There is no way to know without addi-

tional information.

Short Answer

12. Explain how an orbit is formed.

13. Describe how gravity and air resistancecombine when an object reaches terminalvelocity.

14. Explain why friction can make observingNewton’s first law of motion difficult.

Chapter 6156

Chapter Review


Concept Mapping

15. Use the followingterms to create aconcept map: grav-ity, free fall, terminalvelocity, projectilemotion, air resistance.


16. During a shuttle launch, about 830,000 kgof fuel is burned in 8 minutes. The fuelprovides the shuttle with a constantthrust, or push off the ground. How doesNewton’s second law of motion explainwhy the shuttle’s acceleration increasesduring takeoff?

17. When using a hammer to drive a nail intowood, you have to swing the hammerthrough the air with a certain velocity.Because the hammer has both mass andvelocity, it has momentum. Describe whathappens to the hammer’s momentumafter the hammer hits the nail.

18. Suppose you are standing on a skateboardor on in-line skates and you toss a back-pack full of heavy books toward yourfriend. What do you think will happen toyou and why? Explain your answer interms of Newton’s third law of motion.

MATH IN SCIENCE

19. A 12 kg rock falls from rest off a cliff andhits the ground in 1.5 seconds.a. Ignoring air resistance, what is the

rock’s velocity just before it hits theground?

b. What is the rock’s weight after it hitsthe ground? (Hint: Weight is a measureof the gravitational force on an object.)


20. The picture below shows a common desktoy. If you pull one ball up and release it,it hits the balls at the bottom and comesto a stop. In the same instant, the ball onthe other side swings up and repeats thecycle. How does conservation of momen-tum explain how this toy works?




ReadingCheck-up


XA Bat with Dimples

W ouldn’t it be nice to hit a home run every time? Jeff DiTullio, a teacher at

MIT, in Cambridge, Massachusetts, hasfound a way for you to getmore bang from your bat.Would you believe dimples?

Building a Better BatIf you look closely at thesurface of a golf ball, you’llsee dozens of tiny craterlikedimples. When air flowspast these dimples, it getsstirred up. By keeping airmoving near the surface ofthe ball, the dimples helpthe golf ball move fasterand farther through the air.

DiTullio decided to applythis same idea to a baseball bat. His hypothesiswas that dimples would allow a bat to movemore easily through the air. This would helpbatters swing the bat faster and hit the ballharder. To test his hypothesis, DiTullio pressedhundreds of little dimples about 1 mm deepand 2 mm across into the surface of a bat.

When DiTullio tested his dimpled bat in awind tunnel, he found that it could be swung 3 to 5 percent faster. That may not sound likemuch, but it could add about 5 m to a fly ball!

Safe . . . or Out?As you might imagine, many baseball playerswould love to have a bat that could turn a longfly ball into a home run. But are dimpled base-ball bats legal?

The size and shape of every piece of equip-ment used in Major League Baseball games areregulated. A baseball bat, for instance, must beno more than 107 cm long and no more than 7 cm across at its widest point. When DiTullio

designed his dimpled bat, there was no rule stat-ing that bats had to be smooth. But when MajorLeague Baseball found out about the new bat,

they changed the rules! Todayofficial rules require that allbats be smooth, and theyprohibit any type of “experi-mental” bat. Someday therules may be revised to allowDiTullio’s dimpled bat. Whenthat happens, fans of thedimpled baseball bat will allshout, “Play ball!”

Dimple Madness Now that you know howdimples can improve baseballbats, think of other uses fordimples. How might dimples

improve the way other objects move through theair? Draw a sketch of a dimpled object, anddescribe how the dimples improve the design.

Jeff DiTullio,pictured with his dimpledbaseballbat, is anaeronauticalengineer—someone whostudies boththe way airmoves and theway things movethrough air.

Drag

Reduceddrag

By reducing the amount of dragbehind the bat, dimples help thebat move faster through the air.

158Copyright © by Holt, Rinehart and Winston. All rights reserved.

H is West Coaster, which sits on the Santa Monica pier inSanta Monica, California, towers five stories above the

Pacific Ocean. The cars on the Steel Force, at Dorney Park, inPennsylvania, reach speeds of over 120 km/h and drop morethan 60 m to disappear into a 37 m long tunnel. The Mamba, atWorlds of Fun, in Missouri, sends cars flying along as high and asfast as the Steel Force does, but it also has two giant back-to-back hills, a fast spiral, and five “camelback” humps. The camel-backs are designed to pull riders’ seats out from under them,giving the riders “air time.”

Coaster MotionRoller-coaster cars really do coast along the track. A motor pullsthe cars up a high hill to start the ride. After that, the cars arepowered by gravity alone. As the cars roll downhill, they pick upenough speed to whiz through the rest of the curves, loops,twists, and bumps in the track.

Designing a successful coaster is no simple task. Steve Okamotohas to calculate the cars’ speed and acceleration on each part ofthe track. “The coaster has to go fast enough to make it up thenext hill,” he explains. Okamoto uses his knowledge of geometryand physics to create safe but scary curves, loops, humps, anddips. Okamoto must also keep in mind that the ride’s towers andstructures need to be strong enough to support both the track and

Roller coasters have fascinatedSteve Okamoto ever since hisfirst ride on one. “I remembergoing to Disneyland as a kid.My mother was always upsetwith me because I kept look-ing over the sides of the rides,trying to figure out how theyworked,” he laughs. To satisfyhis curiosity, Okamoto becamea mechanical engineer. Todayhe uses his scientific knowl-edge to design and buildmachines, systems, and build-ings. But his specialty is rollercoasters.

ROLLER COASTER DESIGNER

the speeding cars full of people. The carsthemselves need special wheels to keepthem locked onto the track and seatbelts or bars to keep passengers safelyinside. “It’s like putting together a puzzle,except the pieces haven’t been cut outyet,” says Okamoto.

Take the Challenge Step outside for a moment. Gathersome rope and a medium-sized plasticbucket half-full of water. Can you get the bucket over your head and upsidedown without any water escaping? Howdoes this relate to roller coasters?

The Wild Thing, in Shakopee, Minnesota, wasdesigned by Steve Okamoto.


160 Chapter 7

Fluids and Pressure. . . 162MathBreak . . . . . . . . . 162QuickLab. . . . . . . . . . . 166Internet Connect . . . . 167

Buoyant Force . . . . . . 168MathBreak . . . . . . . . . 170QuickLab . . . . . . . . . . 171Geology Connection . . 172Internet Connect . . . . 172

Bernoulli’s Principle . . 173QuickLab . . . . . . . . . . 173Apply . . . . . . . . . . . . . 176

Chapter Review . . . . . . . . . 180


LabBook . . . . . . . . . . . 658–661

A Need for SpeedEven when you are racing downhill on your bicycle, a fluidforce slows you down. “What a drag!” you say. Well, actu-ally, it is a drag. When designing bicycle gear and clothing,manufacturers consider more than just looks and comfort.They also try to decrease drag, a fluid force that opposesmotion. Here a cyclist rides a bike in a wind tunnel in astudy of how a fluid—air—affects his ride. In this chapter,you’ll learn more about forces that fluids exert on objectsin your everyday life.


1. What is a fluid?2. How is fluid pressure

exerted?3. Do moving fluids exert

different forces than nonmoving fluids?

Forces in FluidsForces in Fluids


161

TAKING FLIGHT In this activity, you will build amodel airplane to help you identifyhow wing size affects flight.

Procedure

1. Fold a sheet of paper inhalf lengthwise. Then open it.Fold the top corners toward thecenter crease. Then fold the entire sheet in half along the center crease.

2. With the plane on its side, fold thetop front edge down so that itmeets the bottom edge. Fold thetop edge down again so that itmeets the bottom edge.

3. Turn the plane over. Repeat step 2.

4. Raise both wings so that they areperpendicular to the body.

5. Point the plane slightly upward,and gently throw it. Repeat severaltimes. Describe what you see.

6. Make the wings smaller by foldingthem one more time. Gently throwthe plane. Repeat several times.Describe what you see.

7. Try to achieve the same flight pathyou saw when the wings were bigger. Record your technique.

Analysis

8. What happened to the plane’sflight when you reduced the sizeof its wings? Explain.

9. What gave your plane its forwardmotion?

Forces in FluidsCopyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 7162

Pressure, Force, and AreaThe equation on this pagecan be used to find pressureor rearranged to find force orarea.

Force Pressure AreaForce

Area –––––––Pressure

1. Find the pressure exertedby a 3,000 N crate with anarea of 2 m2.

2. Find the weight of a rockwith an area of 10 m2 thatexerts a pressure of 250 Pa.

(Be sure to express youranswers in the correct SI unit.)

MATH BREAK

Section

1

fluidpressurepascalatmospheric pressuredensityPascal’s principle

Describe how fluids exertpressure.

Analyze how fluid depth affectspressure.

Give examples of fluids flowingfrom high to low pressure.

State and apply Pascal’s principle.

Fluids and PressureWhat does a dolphin have in common with a sea gull? Whatdoes a dog have in common with a fly? What do you havein common with all these living things? The answer is thatyou and all these other living things spend a lifetime mov-ing through and even breathing fluids. A fluid is any materialthat can flow and that takes the shape of its container. Fluidsinclude liquids (such as water and oil) and gases (such as oxy-gen and carbon dioxide). Fluids are able to flow because theparticles in fluids, unlike the particles in solids, can move eas-ily past each other. As you will find out, the remarkable prop-erties of fluids allow huge ships to float, divers to explore theocean depths, and jumbo jets to soar across the skies.

All Fluids Exert PressureYou probably have heard the terms air pressure, water pressure,and blood pressure. Air, water, and blood are all fluids, and allfluids exert pressure. So what’s pressure? Well, think aboutthis example. When you pump up a bicycle tire, you pushair into the tire. And like all matter, air is made of tiny particlesthat are constantly moving. Inside the tire, the air particlespush against each other and against the walls of the tire, asshown in Figure 1. The more air you pump into the tire, themore the air particles push against the inside of your tire.Together, these pushes create a force against the tire. Theamount of force exerted on a given area is pressure. Pressurecan be calculated by dividing the force that a fluid exerts bythe area over which the force is exerted:

Pressure ForceArea

The SI unit for pressure is the pascal. Onepascal (1 Pa) is the force of one new-ton exerted over an area of onesquare meter (1 N/m2). Try theMathBreak at left to practicecalculating pressure.

Figure 1 The force of the air particles hitting the inner surfaceof the tire creates pressure,which keeps the tire inflated.



Why Are Bubbles Round? When you blow a soapbubble, you blow in only one direction. So whydoesn’t the bubble get longer and longer as youblow instead of rounder and rounder? The shapeof the bubble is due in part to an importantproperty of fluids: Fluids exert pressure evenlyin all directions. The air you blow into the bub-ble exerts pressure evenly in every direction, sothe bubble expands in every direction, helpingto create a sphere, as shown in Figure 2. This prop-erty also explains why tires inflate evenly (unless thereis a weak spot in the tire).

Atmospheric PressureThe atmosphere is the layer of nitrogen, oxygen, andother gases that surrounds the Earth. The atmospherestretches about 150 km above us. If you could stack500 Eiffel Towers on top of each other, they wouldcome close to reaching the top of the atmosphere.However, approximately 80 percent of the gases in theatmosphere are found within 10 km of the Earth’s sur-face. Earth’s atmosphere is held in place by gravity,which pulls the gases toward Earth. The pressurecaused by the weight of the atmosphere is calledatmospheric pressure.

Atmospheric pressure is exerted on everything onEarth, including you. The atmosphere exerts a pressureof approximately 101,300 N on every square meter, or101,300 Pa. This means that there is a weight of about10 N (roughly the weight of a pineapple) on everysquare centimeter (roughly the area of the tip of yourlittle finger) of your body. Ouch!

Why don’t you feel this crushing pressure? The flu-ids inside your body also exert pressure, just like theair inside a balloon exerts pressure. Figure 3 can helpyou understand.

Figure 2 You can’t blow a squarebubble, because fluids exert pressureequally in every direction.

163Forces in Fluids

Figure 3 The pressure exerted by the air inside a balloonkeeps the balloon inflated against atmospheric pressure.Similarly, the pressure exerted by the fluid (mostly water)inside your body works against atmospheric pressure.


Atmospheric Pressure Varies At the topof the atmosphere, pressure is almost non-existent because there is no atmospherepressing down. At the top of Mount Everestin south-central Asia (which is the highestpoint on Earth), atmospheric pressure isabout 33,000 Pa, or 33 kilopascals (kPa). At sea level, atmospheric pressure is about101 kPa.

Pressure Depends on Depth As shownin Figure 4, pressure increases as you descendthrough the atmosphere. In other words, thepressure increases as the atmosphere gets“deeper.” This is an important point aboutfluids: Pressure depends on the depth of thefluid. At lower levels of the atmosphere, thereis more fluid above you being pulled byEarth’s gravitational force, so there is morepressure.

If you travel to higher or lower points inthe atmosphere, the fluids in your body haveto adjust to maintain equal pressure. You mayhave experienced this if your ears have“popped” when you were in a plane takingoff or a car traveling down a steep mountainroad. Small pockets of air behind youreardrums contract or expand as atmosphericpressure increases or decreases. The “pop”occurs when air is released due to these pres-sure changes.

At 150,000 m above sea level, atmospheric pressure is almost zero.Humans cannot travel thishigh without protection.The space shuttle travelspast this point on its wayinto orbit.

The atmosphericpressure at 12,000 mis about 20 kPa.Airplane cabins mustbe pressurized forpassenger safety.

At the top of Mount Everest (8,847 mabove sea level), atmospheric pressureis about a third that at sea level.

Atmospheric pressure at La Paz,Bolivia (the world’s highest capitalcity at 4,000 m) is about 51 kPa.

At sea level (0 m), the fullpressure of the atmosphere—101 kPa—is exerted on you.

1. How do particles in a fluid exert pres-sure on a container?

2. Why are you not crushed by atmos-pheric pressure?

3. Applying Concepts Explain why damson deep lakes should be thicker at thebottom than near the top.

REVIEW

Figure 4 Differences in Atmospheric Pressure


Pressure exerted ona diver 10 m belowthe water’s surfaceis twice the pres-sure at the surface.

At 500 m below thesurface, pressure isabout 5,000 kPa. Diversat or below this levelmust wear special suitsto survive the pressure.

The wreck of the Titanic rests 3,660 mbelow sea level. The water pressure atthis depth is 36,600 kPa.

The viper fish lives8,000 m below theocean’s surface. Nofish are found belowthis level. The waterpressure at thisdepth is 80,000 kPa.

In 1960, the Triestedescended to thedeepest part of theocean (11,000 m),where the pressureis 110,000 kPa.

Water Pressure Water is a fluid; therefore, it exerts pressure,just like the atmosphere does. Water pres-sure also increases with depth because ofgravity. Take a look at Figure 5. The deepera diver goes in the water, the greater thepressure becomes because more water abovethe diver is being pulled by Earth’s gravita-tional force. In addition, the atmospherepresses down on the water, so the total pres-sure on the diver includes water pressure aswell as atmospheric pressure.

But pressure does not depend on thetotal amount of fluid present, only on thedepth of the fluid. A swimmer would feelthe same pressure swimming at 5 m belowthe surface of a small pond as at 5 m belowthe surface of an ocean, even though thereis more water in the ocean.

Density Makes a Difference Water isabout 1,000 times more dense than air.(Remember, density is the amount of mat-ter in a certain volume, or mass per unitvolume.) Because water is more dense thanair, a certain volume of water has moremass—and therefore weighs more—than thesame volume of air. Therefore, water exertsgreater pressure than air.

For example, if you climb a 10 m tree,the decrease in atmospheric pressure is too small to notice. But if you dive 10 munderwater, the pressure on you increasesto 201 kPa, which is almost twice the atmos-pheric pressure at the surface!

Figure 5 Differences in Water Pressure

165Forces in Fluids

Fluids Flow from High Pressure to Low PressureLook at Figure 6. When you drink through a straw, you removesome of the air in the straw. Because there is less air, the pres-sure in the straw is reduced. But the atmospheric pressure onthe surface of the liquid remains the same. This creates a dif-ference between the pressure inside the straw and the pressureoutside the straw. The outside pressure forces the liquid upinto the straw and into your mouth. So just by sipping yourdrink through a straw, you can observe another importantproperty of fluids: Fluids flow from regions of high pressureto regions of low pressure.

Go with the Flow Take a deep breath—that’s fluid flowingfrom high to low pressure! When you inhale, a muscle increasesthe space in your chest, giving your lungs room to expand. Thisexpansion lowers the pressure in your lungs so that it becomeslower than the outside air pressure. Air then flows into yourlungs—from higher to lower pressure. This air carries oxygenthat you need to live. Figure 7 shows how exhaling also causesfluids to flow from higher to lower pressure. You can see thissame exchange when you open a carbonated beverage or squeezetoothpaste onto your toothbrush.

166

Figure 6 Atmospheric pressurehelps you sip through a straw!

Figure 7 Just as when youinhale, fluids flow from high tolow pressure when you exhale.

Blown Away

1. Lay an empty plastic sodabottle on its side.

2. Wad a small piece ofpaper (about 4 4 cm)into a ball.

3. Place the paper ball justinside the bottle’s opening.

4. Blow straight into theopening.

5. Record your observationsin your ScienceLog.

6. Explain your results interms of high and low fluid pressures.

When you exhale, a muscle in your chest moves upward,decreasing the space in yourchest.

a

Chapter 7

The decrease in spacecauses the pressure inyour lungs to increase.The air in your lungs flowsfrom a region of higherpressure (your chest) to a region of lower pressure(outside of your body).

b

Exhaled air carries carbon dioxide out of the lungs.

c



Pascal’s PrincipleImagine that the water-pumping station in your town can nowincrease the water pressure by 20 Pa. Will the water pressurebe increased more at a supermarket two blocks away or at ahome 2 km away?

Believe it or not, the increase in waterpressure will be transmitted through all of the water and will be the same—20 Pa—at both locations. Thisis explained by Pascal’s principle,named for Blaise Pascal, theseventeenth-century French scientistwho discovered it. Pascal’s principlestates that a change in pressure atany point in an enclosed fluid willbe transmitted equally to all parts ofthat fluid.

Putting Pascal’s Principle to WorkDevices that use liquids to transmitpressure from one point to another arecalled hydraulic (hie DRAW lik) devices.Hydraulic devices use liquids becausethey cannot be compressed, or squeezed,into a smaller space very much. This prop-erty allows liquids to transmit pressure more effi-ciently than gases, which can be compressed a great deal.

Hydraulic devices can multiply forces. The brakes of a typi-cal car are a good example. In Figure 8, a driver’s foot exertspressure on a cylinder of liquid. Pascal’s principle tells you thatthis pressure is transmitted equally to all parts of the liquid-filledbrake system. This liquid presses a brake pad against each wheel,and friction brings the car to a stop. The force is multipliedbecause the pistons that push the brake pads on each wheel aremuch larger than the piston that is pushed by the brake pedal.

Forces in Fluids 167

1. Explain how atmospheric pressure helps you drink througha straw.

2. What does Pascal’s principle state?

3. Making Predictions When you squeeze a balloon, whereis the pressure inside the balloon increased the most?Explain your answer in terms of Pascal’s principle.

REVIEW

Figure 8 Thanks to Pascal’sprinciple, the touch of a footcan stop tons of moving metal.

NSTA

TOPIC: Fluids and PressureGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP160


Chapter 7168

Buoyant ForceWhy does a rubber duck floaton water? Why doesn’t it sinkto the bottom of your bath-tub? Even if you pushed therubber duck to the bottom, itwould pop back to the surface whenyou released it. Some force pushes therubber duck to the top of the water. Thatforce is buoyant force, the upward force thatfluids exert on all matter.

Air is a fluid, so it exerts a buoyant force. But why don’tyou ever see rubber ducks floating in air? Read on to find out!

Buoyant Force Is Caused byDifferences in Fluid PressureLook at Figure 9. Water exerts fluid pressure onall sides of an object. The pressure exerted hori-zontally on one side of the object is equal to thepressure exerted horizontally on the opposite side.These equal pressures cancel one another. Thus,the only fluid pressures affecting the object are atthe top and at the bottom. Because pressureincreases with depth, the pressure on the bottomof the object is greater than the pressure at thetop, as shown by the width of the arrows.Therefore, the water exerts a net upward force onthe object. This upward force is buoyant force.

Determining Buoyant Force Archimedes (ahrkuh MEE deez), a Greek mathematician who livedin the third century B.C., discovered how to deter-mine buoyant force. Archimedes’ principle statesthat the buoyant force on an object in a fluid is

an upward force equal to the weight of the volume of fluidthat the object displaces. (Displace means “to take the placeof.”) For example, suppose the object in Figure 9 displaces 250 mL of water. The weight of that volume of displaced wateris about 2.5 N. Therefore, the buoyant force on the object is2.5 N. Notice that the weight of the object has nothing to dowith the buoyant force. Only the weight of the displaced fluiddetermines the buoyant force on an object.

Figure 9 There is more fluidpressure on the bottom ofan object because pressureincreases with depth. Thisresults in an upward forceon the object—buoyant force.

Section

2

buoyant forceArchimedes’ principle

Explain the relationship betweenfluid pressure and buoyant force.

Predict whether an object willfloat or sink in a fluid.

Analyze the role of density in an object’s ability to float.

Weight Vs. Buoyant ForceAn object in a fluid will sink if it has a weight greater than theweight of the fluid that is displaced. In other words, an objectwill sink if its weight is greater than the buoyant force actingon it. An object floats only when it displaces a volume of fluidthat has a weight equal to the object’s weight—that is, if thebuoyant force on the object is equal to the object’s weight.

Sinking The lake scene in Figure 10 looks quite peaceful, butthere are forces being exerted! The rock weighs 75 N. It dis-places 5 L of water. According to Archimedes’ principle, thebuoyant force is equal to the weight of the displaced water—about 50 N. Because the rock’s weight is greater than the buoy-ant force, the rock sinks.

Floating The fish weighs 12 N. It displaces a volume ofwater that has a weight of 12 N. Because the fish’s weightis equal to the buoyant force, the fish floats in the water.Now look at the duck. The duck weighs 9 N. The duck doesnot sink. What does that tell you? The buoyant force on theduck must be equal to the duck’s weight. But the duck isn’teven all the way underwater! Only the duck’s feet, legs, andstomach have to be underwater in order to displace enoughwater to equal 9 N. Thus, the duck floats.

Buoying Up If the duck dove underwater, it would then dis-place more water, and the buoyant force would therefore begreater. When the buoyant force on an object is greater thanthe object’s weight, the object is buoyed up (pushed up) out ofthe water until what’s left underwater displaces an amount ofwater that equals the object’s entire weight. That’s why a rub-ber duck pops to the surface when it is pushed to the bottomof a filled bathtub.

169

Weight 9 NBuoyant force 9 NDuck floats on the surface

Weight 75 NBuoyant force 50 NRock sinks

Weight 12 NBuoyant force 12 NFish floats in the water

Figure 10 Will an object sink orfloat? It depends on whether thebuoyant force is less than orequal to the object’s weight.

Find five things that float inwater and five things thatsink in water. What do thefloating objects have in com-mon? What do the sinkingobjects have in common?



An Object Will Float or Sink Based on Its DensityThink again about the rock at the bottom of the lake. Therock displaces 5 L of water, which means that the volume ofthe rock is 5,000 cm3. (Remember that liters are used only forfluid volumes.) But 5,000 cm3 of rock weighs more than anequal volume of water. This is why the rock sinks. Becausemass is proportional to weight on Earth, you can say that therock has more mass per volume than water. Remember, massper unit volume is density. The rock sinks because it is moredense than water. The duck floats because it is less dense thanwater. In Figure 10, the density of the fish is exactly equal tothe density of the water.

More Dense Than Air Think back to the question aboutthe rubber duck: “Why does it float on water but not inair?” The rubber duck floats because it is less dense thanwater. However, most substances are more dense than air.Therefore, there are few substances that float in air. Theplastic that makes up the rubber duck is more dense than

air, so the rubber duck doesn’t float in air.

Less Dense Than Air One substance that is lessdense than air is helium, a gas. In fact, helium isover 70 times less dense than air. A volume ofhelium displaces a volume of air that is much

heavier than itself, so helium floats. That’s whyhelium is used in airships and parade balloons,

like the one shown in Figure 11.

Chapter 7170

Figure 11 Helium in a balloon floatsin air for the same reason a duckfloats in water—it is less dense thanthe surrounding fluid.

How to Calculate DensityThe volume of any sample ofmatter, no matter what stateor shape, can be calculatedusing this equation:

MassDensity –––––––

Volume

1. What is the density of a 20 cm3 sample of liquidwith a mass of 25 g?

2. A 546 g fish displaces 420 cm3 of water. What is the density of the fish?

MATH BREAK


The Mystery of Floating SteelSteel is almost eight times more dense than water. And yethuge steel ships cruise the oceans with ease, even while car-rying enormous loads. But hold on! Didn’t you just learn thatsubstances that are more dense than water will sink in water?You bet! So how does a steel ship float?

The secret is in the shape of the ship. What if a ship werejust a big block of steel, as shown in Figure 12? If you put thatsteel block into water, the block would sink because it is moredense than water. For this reason, ships are built with a hol-low shape, as shown below. The amount of steel in the shipis the same as in the block, but the hollow shape increasesthe volume of the ship. Because density is mass per volume,an increase in the ship’s volume leads to a decrease in its den-sity. Therefore, ships made of steel float because their overalldensity is less than the density of water. This is true of boatsof any size, made of any material. Most ships are actually builtto displace even more water than is necessary for the ship tofloat so that the ship won’t sink when people and cargo areloaded onboard.


Figure 12 A Ship’s Shape Makes the Difference

A block of steel is moredense than water, so itsinks.

Shaping the steel into ahollow form increases thevolume occupied by thesame mass, resulting in areduced overall density ofthe ship. The ship is nowless dense than waterand therefore floats.

The Seawise Giant is thelargest ship in the world. Itis so large that crew mem-bers often use bicycles totravel around the ship.

Ship-Shape

1. Roll a piece of clayinto a ball the sizeof a golf ball, anddrop it into a container ofwater. Record your obser-vations in your ScienceLog.

2. With your hands, flattenthe ball of clay until it is abit thinner than your littlefinger, and press it into theshape of a bowl or canoe.

3. Place the clay boat gentlyin the water. How doesthe change of shape affectthe buoyant force on theclay? How is that changerelated to the average density of the clay boat?Record your answers inyour ScienceLog.


Density on the Move A submarine is a special kind of shipthat can travel on the surface of the water and underwater.Submarines have special tanks that can be opened to allowsea water to flow in. This water adds mass, thus increasing thesubmarine’s overall density so it can descend into the ocean.Crew members can control the amount of water taken in,thereby controlling the submarine’s change in density andthus its depth in the ocean. Compressed air is used to blowthe water out of the tanks so the submarine can rise throughthe water. Most submarines are built of high-strength metalsthat withstand water pressure. Still, most submarines can gono deeper than 400 m below the surface of the ocean.

How Is a Fish Like a Submarine? No, this is not a trickquestion! Like a submarine, some fish adjust their overalldensity in order to stay at a certain depth in the water. Mostbony fish have an organ called a swim bladder, shown inFigure 13. This swim bladder is filled with gases produced inthe fish’s blood. The inflated swim bladder increases the fish’s

volume, thereby decreasing the fish’s overall density andkeeping it from sinking in the water. The fish’s

nervous system controls the amount of gasin the bladder according to the fish’s

depth in the water. Some fish,such as sharks, do not havea swim bladder. These fishmust swim constantly tokeep from sinking to the bottom of the water.

Chapter 7172

Figure 13 Most bony fish havean organ called a swim bladderthat allows the fish to adjust itsoverall density.

1. Explain how differences in fluid pressure create buoyantforce on an object.

2. An object weighs 20 N. It displaces a volume of waterthat weighs 15 N.

a. What is the buoyant force on the object?

b. Will this object float or sink? Explain your answer.

3. Iron has a density of 7.9 g/cm3. Mercury has a densityof 13.6 g/cm3. Will iron float or sink in mercury? Explainyour answer.

4. Applying Concepts Why is it inaccurate to say that allheavy objects will sink in water?

REVIEW

Swim bladder

The rock that makes up the Earth’scontinents is about 15 percent lessdense than the molten (melted)mantle rock below it. Because of thisdifference in densities, the continentsare “floating” on the mantle.


NSTA

TOPIC: The Buoyant ForceGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP165


Bernoulli’s PrincipleHas this ever happened to you? You’ve just turned on the shower.Upon stepping into the water stream, you decide that the waterpressure is not strong enough. You turn the faucet to providemore water, and all of a sudden the bottom edge of the showercurtain starts swirling around your legs. What’s going on? Itmight surprise you that the explanation for this unusual occur-rence also explains how wings help birds and planes fly andhow pitchers throw curve balls.

Fluid Pressure Decreases as Speed Increases The strange reaction of the shower curtain is caused by aproperty of moving fluids that was first described in the eight-eenth century by Daniel Bernoulli (buhr NOO lee), a Swissmathematician. Bernoulli’s principle states that as the speedof a moving fluid increases, its pressure decreases. In the caseof the shower curtain, the faster the water moves, the lesspressure it exerts. This creates an imbalance between the pressure inside the shower curtain and the pressure outside it. Because the pressure outside is now greater than the pressure inside, the shower curtain is pushed toward the water stream.

Science in a Sink You can see Bernoulli’s principle at workin Figure 14. A table-tennis ball is attached to a string andswung gently into a moving stream of water. Instead of beingpushed back out, the ballis actually held in the mov-ing water when the stringis given a tug. Why doesthe ball do that? The wateris moving, so it has a lowerpressure than the sur-rounding air. The higherair pressure then pushesthe ball into the area oflower pressure—the waterstream. Try this at home tosee for yourself!

Figure 14 This ball is pushedby the higher pressure of theair into an area of reducedpressure—the water stream.

173

Section

3

Bernoulli’s principleliftthrustdrag

Describe the relationship betweenpressure and fluid speed.

Analyze the roles of lift, thrust,and drag in flight.

Give examples of Bernoulli’sprinciple in real-life situations.

Breathing Bernoulli-Style

1. Hold two pieces of paperby their top edges, one ineach hand, so that theyhang next to one anotherabout 5 cm apart.

2. Blow a steady stream of airbetween the two sheets ofpaper.

3. Record your observations in your ScienceLog. Explainthe results according toBernoulli’s principle.


It’s a Bird! It’s a Plane! It’s Bernoulli’s Principle!The most common commercial airplane in the skies today isthe Boeing 737 jet. A 737 jet is almost 37 m long and has awingspan of 30 m. Even without passengers, the plane weighs350,000 N. That’s more than 35 times heavier than an aver-age car! How can something so big and heavy get off theground, much less fly 10,000 m into the sky? Wing shapeplays a role in helping these big planes—as well as smallerplanes and even birds—achieve flight, as shown in Figure 15.

According to Bernoulli’s principle, the faster-moving airabove the wing exerts less pressure than the slower-movingair below the wing. The increased pressure that results belowthe wing exerts an upward force. This upward force, knownas lift, pushes the wings (and the rest of the airplane or bird)upward against the downward pull of gravity.

Chapter 7174

Figure 15 Wing Shape Creates Differences in Air Speed

The first successful flight ofan engine-driven heavier-than-air machine occurredin Kitty Hawk, NorthCarolina, in 1903. OrvilleWright was the pilot. Theplane flew only 37 m (aboutthe length of a 737 jet)before landing, and theentire flight lasted only 12 seconds.

The curved top of the wingforces air passing above the wingto travel a longer distance thanthe air passing below the wing.

The air above must speed up toconverge with the air below at thetail end of the wing. Therefore,the air moving above the wingmust move faster than the airbelow it.

As the wing moves through thesky, air passing below the wingtravels in a fairly straight path.

a

b

c


Thrust and Wing Size Determine Lift The amount of lift created by a plane’s wing is deter-mined in part by the size of the wing and the speed atwhich air travels around the wing. The speed of an airplaneis in large part determined by its thrust—the forward forceproduced by the plane’s engine. In general, a plane with agreater amount of thrust moves faster than a plane with lessthrust. This faster speed means air travels around the wing ata greater speed, which increases lift.

You can understand the relationship between wing size,thrust, and speed by thinking about a jet plane, like the onein Figure 16. This plane is able to fly with a relatively smallwing size because its engine creates an enormous amount ofthrust. This thrust pushes the plane through the sky at tremen-dous speeds. Therefore, the jet generates sufficient lift with smallwings by moving very quickly through the air. Smaller wingskeep a plane’s weight low, which also contributes to speed.

Compared with the jet, a glider, like the one in Figure 17,has a large wing area. A glider is an engineless plane that ridesrising air currents to stay in flight. Without engines,gliders produce no thrust and move more slowlythan many other kinds of planes. Thus, a glidermust have large wings to create the lift necessaryto keep it in the air.

Bernoulli’s Principle Is for the Birds Birds don’t haveengines, of course, so they must flap their wings to

push themselves through the air. The hawk shownat left uses its large wing size to fly with a mini-

mum of effort. By extending its large wings totheir full length and gliding on wind currents, ahawk can achieve enough lift to stay in the air

while flapping only occasionally. Smallerbirds must flap their wings more often to

stay in the air.


Figure 17 The wings of thisglider are very large in order tomaximize the amount of liftachieved.

Soaring science! See how wingshape affects the flight of your

own airplane on page 661of the LabBook.

Figure 16 The engine of this jetcreates a great deal of thrust, so the wings don’t have to be very big.

Self-CheckDoes air travel faster or slowerover the top of a wing? (Seepage 724 to check your answer.)

Drag Opposes Motion in Fluids Have you ever walked into a strong wind and noticed that thewind seemed to slow you down? Fluids exert a force that

opposes motion. The force that opposes or restricts motionin a fluid is called drag. In a strong wind, air “drags” on

your clothes and body, making it difficult for you tomove forward. Drag forces in flight work against theforward motion of a plane or bird and are usuallycaused by an irregular flow of air around the wings.An irregular or unpredictable flow of fluids is knownas turbulence.

Lift is often reduced when turbulence causesdrag. At faster speeds, drag can become a seriousproblem, so airplanes are equipped with ways toreduce turbulence as much as possible when in flight. For example, flaps like those shown inFigure 18 can be used to change the shape or areaof a wing, thereby reducing drag and increasing lift.

Similarly, birds can adjust their wing feathers inresponse to turbulence to achieve greater lift.

Chapter 7176

Lift and Spoilers

At high speeds, air moving around the body ofthis race car could lift the car just as it lifts aplane’s wing. This could cause the wheels to lose contactwith the ground, sending the car out of control. To prevent thissituation, an upside-down wing, or spoiler, is mounted on the rearof the car. How do spoilers help reduce the danger of accidents?

Figure 18 During flight, the pilot ofthis airplane can adjust these flapsto help increase lift.



Wings Are Not Always Required You don’t have to look up at a bird or a plane flying throughthe sky to see Bernoulli’s principle in your world. In fact,you’ve already learned how Bernoulli’s principle can affectsuch things as shower curtains and race cars. Any time fluidsare moving, Bernoulli’s principle is at work. In Figure 19, youcan see how Bernoulli’s principle can mean the differencebetween a home run and a strike during a baseball game.


1. Does fluid pressure increase or decrease as fluidspeed increases?

2. Explain how wing shape can contribute to liftduring flight.

3. What force opposes motion through a fluid?

4. Interpreting Graphics When the space throughwhich a fluid flows becomes narrow, fluid speedincreases. Explain how this could lead to a col-lision for the two boats shown at right.

Figure 19 A pitcher can take advantage of Bernoulli’s principle toproduce a confusing curveball that is difficult for the batter to hit.

Direction of airflow

Direction of spin

Bernoulli’s principle at play—read how Frisbees® wereinvented on page 182.

Air speed on the left side of the ball is decreasedbecause air being dragged around the ball moves inthe opposite direction of the airflow. This results in aregion of increased pressure on the left side of the ball.

Air speed on the right side of the ball is increasedbecause air being dragged around the ball moves in thesame direction as the airflow. This results in a region ofdecreased pressure on the right side of the ball.

Because air pressure on the leftside is greater than that on theright side, the ball is pushedtoward the right in a curved path.

a

b c

REVIEW

Chapter Highlights

Chapter 7178

SECTION 1 SECTION 2

Vocabularyfluid (p. 162)

pressure (p. 162)

pascal (p. 162)

atmospheric pressure (p. 163)

density (p. 165)

Pascal’s principle (p. 167)

Section Notes

• A fluid is any material thatflows and that takes theshape of its container.

• Pressure is force exerted on agiven area.

• Moving particles of mattercreate pressure by collidingwith one another and withthe walls of their container.

• Fluids exert pressure equallyin all directions.

• The pressure caused by theweight of Earth’s atmosphereis called atmosphericpressure.

• Fluid pressure increases asdepth increases.

• Fluids flow from areas ofhigh pressure to areas of lowpressure.

• Pascal’s principle states that achange in pressure at anypoint in an enclosed fluidwill be transmitted equally toall parts of the fluid.

• Hydraulic devices transmitchanges of pressure throughliquids.

Vocabularybuoyant force (p. 168)

Archimedes’ principle (p. 168)

Section Notes

• All fluids exert an upwardforce called buoyant force.

• Buoyant force is caused bydifferences in fluid pressure.

• Archimedes’ principle statesthat the buoyant force on anobject is equal to the weightof the fluid displaced by theobject.

Skills CheckMath ConceptsPRESSURE If an object exerts a force of 10 Nover an area of 2 m2, the pressure exerted canbe calculated as follows:

Pressure = FAorrecae

= 210

mN2

= , or 5 Pa

Visual Understanding ATMOSPHERIC PRESSURE Why aren’t youcrushed by atmospheric pressure? Figure 3 onpage 163 can help you understand.

BUOYANT FORCE To understand howdifferences in fluid pressure cause buoyantforce, review Figure 9 on page 168.

BERNOULLI’S PRINCIPLE AND WING SHAPETurn to page 174 to review how a wing is oftenshaped to take advantageof Bernoulli’s principle in creating lift.

5 N1 m2


SECTION 3

VocabularyBernoulli’s principle (p. 173)

lift (p. 174)

thrust (p. 175)

drag (p. 176)

Section Notes

• Bernoulli’s principle statesthat fluid pressure decreasesas the speed of a movingfluid increases.

• Wings are often shaped toallow airplanes to takeadvantage of decreased pres-sure in moving air in orderto achieve flight.

• Lift is an upward force thatacts against gravity.

• Lift on an airplane is deter-mined by wing size andthrust (the forward forceproduced by the engine).

• Drag opposes motionthrough fluids.

LabsTaking Flight (p. 661)

SECTION 2

• Any object that is moredense than the surroundingfluid will sink; any objectthat is less dense than thesurrounding fluid will float.

LabsFluids, Force, and Floating (p. 658)

Density Diver (p. 660)


TOPIC: Submarines and Undersea Technology sciLINKS NUMBER: HSTP155

TOPIC: Fluids and Pressure sciLINKS NUMBER: HSTP160

TOPIC: The Buoyant Force sciLINKS NUMBER: HSTP165

TOPIC: Bernoulli’s Principle sciLINKS NUMBER: HSTP170



KEYWORD: HSTFLU

179Forces in FluidsCopyright © by Holt, Rinehart and Winston. All rights reserved.


To complete the following sentences, choosethe correct term from each of the pair ofterms listed below:

1. ? increases with the depth of a fluid.(Pressure or Lift)

2. A plane’s engine produces ? to pushthe plane forward. (thrust or drag)

3. Force divided by area is known as ? .(density or pressure)

4. The hydraulic brakes of a car transmit pressure through fluid. This is an exampleof ? . (Archimedes’ principle or Pascal’sprinciple)

5. Bernoulli’s principle states that the pres-sure exerted by a moving fluid is ? (greater than or less than) the pressure ofthe fluid when it is not moving.


Multiple Choice

6. The curve on the top of a wing a. causes air to travel farther in the same

amount of time as the air below thewing.

b. helps create lift.c. creates a low-pressure zone above the

wing.d. All of the above

7. An object displaces a volume of fluid that a. is equal to its own volume.b. is less than its own volume. c. is greater than its own volume.d. is more dense than itself.

8. Fluid pressure is always directed a. up. c. sideways.b. down. d. in all directions.

9. If an object weighing 50 N displaces a vol-ume of water with a weight of 10 N, whatis the buoyant force on the object?a. 60 Nb. 50 Nc. 40 Nd. 10 N

10. A helium-filled balloonwill float in air becausea. there is more air

than helium.b. helium is less

dense than air.c. helium is as dense

as air.d. helium is more dense

than air.

11. Materials that can flow to fit their containers includea. gases.b. liquids.c. both gases and liquids.d. neither gases nor liquids.

Short Answer

12. What two factors determine the amountof lift achieved by an airplane?

13. Where is water pressure greater, at a depthof 1 m in a large lake or at a depth of 2 min a small pond? Explain.

14. Is there buoyant force on an object at the bottom of an ocean? Explain your reasoning.

15. Why are liquids used in hydraulic brakesinstead of gases?


Concept Mapping

16. Use the followingterms to create aconcept map: fluid,pressure, depth,buoyant force,density.


17. Compared with an empty ship, will a shiploaded with plastic-foam balls float higheror lower in the water? Explain your reasoning.

18. Inside all vacuum cleaners is a high-speedfan. Explain how this fan causes dirt to bepicked up by the vacuum cleaner.

19. A 600 N clown on stilts says to two 600 Nclowns sitting on the ground, “I am exert-ing twice as much pressure as the two ofyou together!” Could this statement betrue? Explain your reasoning.

MATH IN SCIENCE

20. Calculate the area of a 1,500 N object thatexerts a pressure of 500 Pa (N/m2). Thencalculate the pressure exerted by the sameobject over twice that area. Be sure toexpress your answers in the correct SI unit.


Examine the illustration of an iceberg below,and answer the questions that follow.

21. At what point (a, b, or c) is water pressuregreatest on the iceberg?

22. How much of the iceberg has a weightequal to the buoyant force?a. all of itb. the section from a to bc. the section from b to c

23. How does the density of ice compare withthe density of water?

24. Why do you think icebergs are sodangerous to passing ships?


a

b

c



ReadingCheck-up


182

Stayin’ Aloft—The Story of the Frisbee

W hoa! Nice catch! Your friend 30 m away just sent a disk spinning

toward you. As youreached for it, a gust of windfloated it up over your head.With a quick jump, yousnagged it. A snap of yourwrist sends the disksoaring back. You are“Frisbee-ing,” a gamemore than 100 yearsold. But back then,there were no plasticdisks, only pie plates.

From Pie Plate...In the late 1800s, ready-made pies baked in tin platesbegan to appear in stores andrestaurants. A bakery near YaleUniversity, in New Haven, Connecticut,embossed its name, Frisbie’s Pies, on its pieplates. When a few fun-loving college studentstossed empty pie plates, they found that themetal plates had a marvelous ability to stay inthe air. Soon the students began alerting theircompanions of an incoming pie plate by shout-ing “Frisbie!” So tossing pie plates becameknown as Frisbie-ing. By the late 1940s, thegame was played across the country.

…to PlasticIn 1947, California businessmen Fred Morrisonand Warren Franscioni needed to make a littleextra money. They were familiar with pie-plate

tossing, and they knewthe plates oftencracked when theylanded and devel-oped sharp edges

that caused injuries.

At the time, plastic was becoming widely avail-able. Plastic is more durable and flexible

than metal, and it isn’t as likely toinjure fingers. Why not make a

“pie plate” out of plastic,thought Morrison and

Franscioni? They did, andtheir idea was a hugesuccess.

Years later, a toycompany bought therights to make the toy.One day the presidentof the company heard

someone yelling“Frisbie!” while tossing

a disk and decided to usethat name, changing the

spelling to “Frisbee.”

Saucer ScienceIt looks simple, but Frisbee flight is quite com-plicated. It involves thrust, the force you givethe disk to move it through the air; angle ofattack, the slight upward tilt you give the diskwhen you throw it; and lift, the upward forces(explained by Bernoulli’s principle) acting onthe Frisbee to counteract gravity. But perhapsthe most important aspect of Frisbee physics isspin, which gives the Frisbee stability as it flies.The faster a Frisbee spins, the more stable it isand the farther it can fly.

What Do You Think? From what you’ve learned in class, why doyou think the Frisbee has a curved lip? Would acompletely flat Frisbee fly as well? Why or whynot? Find out more about the interesting aero-dynamics of Frisbee flight. Fly a Frisbee for theclass, and explain what you’ve learned.

®


183

“Wet Behind the Ears”

by Jack C. Haldeman II

W illie Joe Thomas is a college student who lied to get into college and

cheated to get a swimming scholar-ship. Now he is faced with a major swim meet,and his coach has told him that he has to swimor be kicked off the team. Willie Joe could losehis scholarship. What’s worse, he would have toget a job.

“Wet Behind the Ears” is Willie Joe’s story. It’s the story of someone who has always takenthe easy way (even if it takes more work), ofsomeone who lies and cheats as easily as hebreathes. Willie Joe could probably do thingsthe right way, but it never even occurred to himto try it!

So when Willie Joe’s roommate, FrankEmerson, announces that he has made anamazing discovery in the chemistry lab, WillieJoe doesn’t much care. Frank works too hard.Frank follows the rules. Willie Joe isn’timpressed.

But when he is running late for the all-important swim meet, Willie Joe rememberswhat Frank’s new compound does. Frank said itwas a “sliding compound.” Willie Joe may notknow chemistry, but “slippery” he understands.And Frank also said something about selling thestuff to the Navy to make its ships go faster.Hey, if it works for ships . . .

See what happens when Willie Joe tries tosave his scholarship. Go to the Holt Anthologyof Science Fiction, and read “Wet Behind theEars,” by Jack C. Haldeman II.


T I M E L I N E

U N I T Work, Machines,and Energy

Unit 3184

3Around

200 B.C.Under the Han

dynasty, the Chinesebecome one of thefirst civilizations to use coal as fuel.

1926American scientist RobertGoddard launches the first

rocket powered by liquid fuel.It reaches a height of 56 m and a speed of 97 km/h.

1948Maria Telkes, a Hungarian-born physicist, designs theheating system for the first

solar-heated house.

1972The first American self-service

gas station opens.

Around

3000 B.C.The sail is used inEgypt. Sails use the

wind rather than humanpower to move boats

through the water.

an you imagineliving in a world

with no machines? Inthis unit, you willexplore the scientificmeaning of work andlearn how machinesmake work easier. Youwill find out howenergy allows you todo work and how dif-ferent forms of energycan be converted intoother forms of energy.You will also learnabout heat and howheating and coolingsystems work. Thistimeline shows someof the inventions anddiscoveries madethroughout history aspeople have advancedtheir understanding ofwork, machines, andenergy.

C


1776The American colonies

declare theirindependence from

Great Britain.

1893The zipper is patented.

1908The automobile age

begins with the massproduction of the Ford

Model T.

1988The world’s most powerful wind-powered

generator begins generating electricalenergy in Scotland’s Orkney Islands.

2000The 2000 Olympic

Summer Games are held in Sydney, Australia.

1656Dutch scientist

Christiaan Huygensinvents the

pendulum clock.

1818The first two-wheeled, rider-propelled machine is

invented by German Baron Karl von Drais deSauerbrun. Made of wood, this early machinepaves the way for the invention of the bicycle.

Work, Machines, and Energy 185Copyright © by Holt, Rinehart and Winston. All rights reserved.

186 Chapter 8

Work and Power . . . . 188MathBreak . . . . . . . . . 190QuickLab . . . . . . . . . . 191Internet Connect . . . . 191

What Is a Machine? . . 192MathBreak . . . . . . . . . 196Apply . . . . . . . . . . . . . 197Internet Connect . . . . 197

Types of Machines . . . 198Internet Connect . . . . 205

Chapter Review . . . . . . . . . 208


LabBook . . . . . . . . . . . 662–667

“One, two, stroke!”. . . . . . shouts the coach as the team races to the finish line.This paddling team is competing in Hong Kong’s annualDragon Boat Races. The Dragon Boat Festival is a 2,000-year-old Chinese tradition that commemorates the death of the national hero, Qu Yuan. The paddlers you see hereare using the paddles to move the boat forward. Eventhough they are celebrating by racing their dragon boat, in scientific terms this team is doing work. How is this possible? Read on to find out!

Work andMachinesWork andMachines

1. What does it mean to dowork?

2. How are machines helpfulwhen doing work?

3. What are some examplesof simple machines?



187

C’MON, LEVER A LITTLE! In this activity, you will use a simplemachine, a lever, to make your taska little easier.

Procedure

1. Gather a few books andstack them on a table, oneon top of the other.

2. Slide your index finger underneaththe edge of the bottom book.Using only the force of your finger,try to lift one side of the books 2or 3 cm off the table. Is it difficult?Write your observations in yourScienceLog.

3. Slide the end of a wooden rulerunderneath the edge of the bottom book. Then slip a largepencil eraser under the ruler.

4. Again using only your index finger,push down on the edge of theruler and try to lift the books.Record your observations.

Caution: Push down slowly tokeep the ruler and eraser from flipping.

Analysis

5. Which was easier, lifting the bookswith your finger or with the ruler?Explain.

6. What was different about the direction of the force your fingerapplied on the books comparedwith the direction of the force you applied on the ruler?

Work and MachinesCopyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 8188

Work and PowerSuppose your science teacher has just given you a homeworkassignment. You have to read an entire chapter by tomorrow!Wow, that’s a lot of work, isn’t it? Actually, in the scientificsense, you won’t be doing any work at all! How can that be?

The Scientific Meaning of WorkIn science, work occurs when a force causes an object to movein the direction of the force. In the example above, you mayput a lot of mental effort into doing your homework, but youwon’t be using a force to move an object. Therefore, in thescientific sense, you will not be doing work.

Now think about the example shown inFigure 1. This student is having a lot of fun,isn’t she? But she is doing work, even thoughshe is having fun. That’s because she’s apply-ing a force to the bowling ball to make it movethrough a distance. However, it’s important tounderstand that she is doing work on the ballonly as long as she is touching it. The ball willcontinue to move away from her after shereleases it, but she will no longer be doingwork on the ball because she will no longer beapplying a force to it.

Working Hard or Hardly Working? You should understandthat applying a force doesn’t always result in work being done.Suppose your neighbor asks you to help push his stalled car.You push and push, but the car doesn’t budge. Even thoughyou may be exhausted and sweaty, you haven’t done any workon the car. Why? Because the car hasn’t moved. Remember,work is done on an object only when a force makes that objectmove. In this case, your pushing doesn’t make the car move.You only do work on the car if it starts to move.

Figure 1 You might be surprised tofind out that bowling is doing work!

Section

1

work powerjoule watt

Determine when work is beingdone on an object.

Calculate the amount of workdone on an object.

Explain the difference betweenwork and power.


Force and Motion in the Same Direction Suppose you’rein the airport and you’re late for a flight. You have to runthrough the airport carrying a heavy suitcase. Because you’remaking the suitcase move, you’re doing work on it, right?Wrong! For work to be done, the object must move in thesame direction as the force. In this case, the motion is in adifferent direction than the force, as shown in Figure 2. So nowork is done on the suitcase. However, work is done on thesuitcase when you lift it off the ground.

You’ll know that work is done on an object if two thingsoccur: (1) the object moves as a force is applied and (2) thedirection of the object’s motion is the same as the directionof the force applied. The pictures and the arrows in the chartbelow will help you understand how to determine when workis being done on an object.

Figure 2 You exert an upwardforce on the suitcase. But themotion of the suitcase is forward.Therefore, you are not doingwork on the suitcase.


Self-CheckIf you pulled awheeled suitcaseinstead of carrying it,would you be doingwork on the suitcase?Why or why not? (Seepage 724 to check your answer.)

Example Direction Direction Doing work?of force of motion

Yes

Yes

No

No

Directionof force

Direction of motion

Work or Not Work?


Calculating WorkDo you do more work when you lift an 80 N barbell or a 160 N barbell? It would be tempting to say that you do morework when you lift the 160 N barbell because it weighs more.But actually, you can’t answer this question with the informa-tion given. You also need to know how high each barbell isbeing lifted. Remember, work is a force applied through a dis-tance. The greater the distance through which you exert a givenforce, the more work you do. Similarly, the greater the forceyou exert through a given distance, the more work you do.

The amount of work (W ) done in moving an object canbe calculated by multiplying the force (F) applied to the objectby the distance (d) through which the force is applied, as shownin the following equation:

W F d

Recall that force is expressed in newtons, and the meter is thebasic SI unit for length or distance. Therefore, the unit usedto express work is the newton-meter (N•m), which is moresimply called the joule (J). Look at Figure 3 to learn more aboutcalculating work. You can also practice calculating work your-self by doing the MathBreak on this page.

The force needed to lift an objectis equal to the gravitational forceon the object—in other words, theobject’s weight.

Increasing the amount of forceincreases the amount of workdone.

Increasing the distance alsoincreases the amount of workdone.

Figure 3 Work Depends on Force and Distance

Chapter 8190

Working It OutUse the equation for workshown on this page to solvethe following problems:

1. A man applies a force of500 N to push a truck 100 m down the street.How much work does he do?

2. In which situation do youdo more work?a. You lift a 75 N bowling

ball 2 m off the floor. b. You lift two 50 N bowl-

ing balls 1 m off thefloor.

MATH BREAK

W 80 N 1 m 80 J W 160 N 1 m 160 J W 80 N 2 m 160 J


More Power to You

1. Use a loop of stringto attach a springscale to a book.

2. Slowly pull the book acrossa table by the spring scale.Use a stopwatch to deter-mine the time this takes.In your ScienceLog, recordthe amount of time it tookand the force used as thebook reached the edge ofthe table.

3. With a metric ruler, meas-ure the distance you pulledthe book.

4. Now quickly pull the bookacross the same distance.Again record the time andforce.

5. Calculate work and powerfor both trials.

6. How were the amounts ofwork and power affectedby your pulling the bookfaster? Record your answersin your ScienceLog.

Power—How Fast Work Is DoneLike work, the term power is used a lot in everyday languagebut has a very specific meaning in science. Power is the rateat which work is done. To calculate power (P), you divide theamount of work done (W ) by the time (t) it takes to do thatwork, as shown in the following equation:

P Wt

You just learned that the unit for work is the joule, andthe basic unit for time is the second. Therefore, the unit usedto express power is joules per second (J/s), which is more sim-ply called the watt (W). So if you do 50 J of work in 5 seconds,your power is 10 J/s, or 10 W. You can calculate your ownpower in the QuickLab at right.

Increasing Power Power is how fast work happens. Poweris increased when more work is done in a given amount oftime. Power is also increased when the time it takes to do acertain amount of work is decreased, as shown in Figure 4.

1. Work is done on a ball when a pitcher throws it. Is thepitcher still doing work on the ball as it flies through theair? Explain.

2. Explain the difference between work and power.

3. Doing Calculations You lift a chair that weighs 50 N toa height of 0.5 m and carry it 10 m across the room.How much work do you do on the chair?

Figure 4 No matter how fast you can sand with sandpaper, anelectric sander can do the same amount of work faster. Therefore,the electric sander has more power.


REVIEW

NSTA

TOPIC: Work and PowerGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP180


What Is a Machine?Imagine you’re in the car with your momon the way to a party when suddenly—KABLOOM hisssss—a tire blows out. “NowI’m going to be late!” you think as your mompulls over to the side of the road. You watchas she opens the trunk and gets out a jack and a tire iron. Sheplaces the jack under the car at the proper location and turnsthe handle until the car just starts to lift off the ground. Usingthe tire iron, she pries off the hubcap and loosens the lug nutsthat hold the wheel. Next, she turns the handle on the jackuntil the car is no longer touching the ground and carefullyremoves the lug nuts and then the wheel. After exchangingthe flat tire with the spare and replacing and tightening thelug nuts, she lowers and removes the jack, tightens the lug

nuts once again, and puts the hubcap back on the wheel.“Wow!” you think, “That wasn’t as hard as I thought

it would be.” As your mom drops you off at theparty, you think how lucky it was that she had

the right equipment to change the tire.

Machines—Making Work EasierNow imagine changing a tire without the jack and thetire iron. Would it have been so easy? No, you wouldhave needed several people just to hold up the car!

Sometimes you need a little help to do work. That’swhere machines come in. A machine is a

device that helps make work easier bychanging the size or direction of a force.

When you think of machines, youmight think of things like cars, big con-struction equipment, or even computers.But not all machines are complicated oreven have moving parts. In fact, the tireiron, jack, and lug nut shown above areall machines. Even the items shown inFigure 5 are machines.

Figure 5 You might besurprised to find out thatall of these commonobjects are machines.

192 Chapter 8

Section

2

machinework inputwork outputmechanical advantagemechanical efficiency

Explain how a machine makeswork easier.

Describe and give examples ofthe force-distance trade-off thatoccurs when a machine is used.

Calculate mechanical advantage.

Explain why machines are not 100 percent efficient.



Work In, Work Out Suppose you need toget the lid off a can of paint. What do youdo? Well, one way to pry the lid off is to usethe flat end of a common machine knownas a screwdriver, as shown in Figure 6. Youplace the tip of the screwdriver under theedge of the lid and then push down on thehandle. The other end of the screwdriver liftsthe lid as you push down. In other words,you do work on the screwdriver, and thescrewdriver does work on the lid. This exam-ple illustrates that two kinds of work arealways involved when a machine is used—the work done on the machine and the work the machine does on another object.

Remember that work is a force applied through a distance.Look again at Figure 6. The work you do on a machine iscalled work input. You apply a force, called the input force, tothe machine and move it through a distance. The work doneby the machine is called work output. The machine applies aforce, called the output force, through a distance. The outputforce opposes the forces you and the machine are workingagainst—in this case, the weight of the lid and the frictionbetween the can and the lid.

How Machines Help You might think that machines helpyou because they increase the amount of work done. But that’snot true. If you multiplied the forces by the distances throughwhich they are applied in Figure 6 (remember, W F d ),you would find that the screwdriver does not do more workon the lid than you do on the screwdriver. Work output cannever be greater than work input.

Input force


Output force

Figure 6 When you use amachine, you do work on themachine, and the machine does work on something else.

The width of the arrowsrepresenting input forceand output force indicatesthe relative size of theforces. The length of thearrows indicates the dis-tance through which theyare exerted.


Machines Do Not Save Work Machines make work easierbecause they change the size or direction of the input force.And using a screwdriver to open a paint can changes boththe size and direction of the input force. Just remember thatusing a machine does not mean that you do less work. Asyou can see in Figure 7, the same amount of work is involvedwith or without the ramp. The ramp decreases the amountof input force necessary to do the work of lifting the box.But the distance over which the force is exerted increases. Inother words, the machine allows a smaller force to be appliedover a longer distance.

The Force-Distance Trade-off When a machine changes thesize of the force, the distance through which the force is exertedmust also change. Force or distance can increase, but nottogether. When one increases, the other must decrease. This isbecause the work output is never greater than the work input.

The diagram on the next page will help you better under-stand this force-distance trade-off. It also shows that somemachines affect only the direction of the force, not the sizeof the force or the distance through which it is exerted.

Figure 7 A simple plank of wood acts as a machine when it is used to help raise a load.

Chapter 8194

Force: 450 N Distance: 1 m Force: 150 N Distance: 3 m

W 450 N 1 m 450 J W 150 N 3 m 450 J

Lifting this box straight up requires aninput force equal to the weight of the box.

Using a ramp to lift the box requires an input force lessthan the weight of the box, but the input force must beexerted over a greater distance.



Small force Large force applied (indicated by arrow over a short distancewidth) applied over a long distance

Large force applied Small force applied over a short distance over a long distance

Small force applied Small force applied over a long distance over a long distance

in the opposite direction

Small force applied Large force applied over a long distance over a short distance

in the opposite direction

Increases force

Decreases force

Changes direction of force

Changes sizeand direction

of force

Machines Change the Size or Direction (or Both) of a Force

Work input Machine Work output Example


Mechanical AdvantageDo some machines make work easier than others? Yes, becausesome machines can increase force more than others. A ma-chine’s mechanical advantage tells you how many times themachine multiplies force. In other words, it compares the inputforce with the output force. You can find mechanical advan-tage by using the following equation:

Mechanical advantage (MA)

Take a look at Figure 8. In this example, the output forceis greater than the input force. Using the equation above, youcan find the mechanical advantage of the handcart:

MA 10

Because the mechanical advantage of the handcart is 10,the output force is 10 times bigger than the input force. Thelarger the mechanical advantage, the easier a machine makesyour work. But as mechanical advantage increases, the distancethat the output force moves the object decreases.

Remember that some machines only change the directionof the force. In such cases, the output force is equal to theinput force, and the mechanical advantage is 1. Other machineshave a mechanical advantage that is less than 1. That meansthat the input force is greater than the output force. Althoughsuch a machine actually decreases your force, it does allow youto exert the force over a longer distance, as shown in Figure 9.

500 N50 N

output forceinput force

Chapter 8196

Finding the Advantage1. You apply 200 N to a

machine, and the machineapplies 2,000 N to anobject. What is themechanical advantage?

2. You apply 10 N to amachine, and the machineapplies 10 N to anotherobject. What is themechanical advantage?Can such a machine beuseful? Why or why not?

3. Which of the followingmakes work easier to do?a. a machine with a

mechanical advantage of 15

b. a machine to which youapply 15 N and thatexerts 255 N

MATH BREAK

Input force 50 N Output

force 500 N

Figure 9 With chopsticksyou can pick up a big bite offood with just a little wiggleof your fingers.

Figure 8 A machine that has alarge mechanical advantage canmake lifting a heavy load awhole lot easier.


Mechanical EfficiencyAs mentioned earlier, the work out-put of a machine can never begreater than the work input. In fact,the work output of a machine isalways less than the work input.Why? Because some of the workdone by the machine is used to over-come the friction created by the useof the machine. But keep in mindthat no work is lost. The work out-put plus the work done to overcomefriction equals the work input.

The less work a machine has todo to overcome friction, the moreefficient it is. Mechanical efficiency(e FISH uhn see) is a comparison of a machine’s work output with the work input. A machine’smechanical efficiency is calculated using the following equation:

Mechanical efficiency 100

The 100 in this equation means that mechanical efficiencyis expressed as a percentage. Mechanical efficiency tells youwhat percentage of the work input gets converted into workoutput. No machine is 100 percent efficient, but reducing theamount of friction in a machine is a way to increase its mechani-cal efficiency. Inventors have tried for many years to create amachine that has no friction to overcome, but so far they havebeen unsuccessful. If a machine could be made that had 100percent mechanical efficiency, it would be called an ideal machine.

work outputwork input

1. Explain how using a ramp makes work easier.

2. Why can’t a machine be 100 percent efficient?

3. Suppose you exert 15 N on a machine, and the machineexerts 300 N on another object. What is the machine’smechanical advantage?

4. Comparing Concepts For the machine described in ques-tion 3, how does the distance through which the outputforce is exerted differ from the distance through whichthe input force is exerted?

197Work and Machines

REVIEW

Oil Improves Efficiency

Car manufacturers recommend regular oilchanges. That’s because over time, motoroil in a car’s engine starts to get dark andthick and doesn’t flow as well as freshmotor oil. Why do you think a car engineneeds motor oil? How does getting regularoil changes improve the mechanical effi-ciency of a car’s engine?

NSTA

TOPIC: Mechanical EfficiencyGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP185

When the fulcrum is closer to theload than to the input force, amechanical advantage ofgreater than 1 results. The out-put force is increased because itis exerted over a shorter distance.

Chapter 8198

Types of MachinesAll machines are constructed from these six simple machines:lever, inclined plane, wedge, screw, wheel and axle, and pulley.You’ve seen a couple of these machines already—a screwdrivercan be used as a lever, and a ramp is an inclined plane. Inthe next few pages, each of the six simple machines will bediscussed separately. Then you’ll learn how compoundmachines are formed from combining simple machines.

LeversHave you ever used the claw end of a hammer to remove anail from a piece of wood? If so, you were using the hammeras a lever. A lever is a simple machine consisting of a bar thatpivots at a fixed point, called a fulcrum. Levers are used toapply a force to a load. There are three classes of levers, basedon the locations of the fulcrum, the load, and the input force.

First Class Levers With a first class lever, the fulcrum isbetween the input force and the load, as shown in Figure 10.First class levers always change the direction of the input force.And depending on the location of the fulcrum, first class leverscan be used to increase force or to increase distance. Someexamples of first class levers are shown below.

When the fulcrum is exactly inthe middle, a mechanical advan-tage of 1 results. The outputforce is not increased becausethe input force’s distance is notincreased.

When the fulcrum is closer to theinput force than to the load, amechanical advantage of lessthan 1 results. Although theoutput force is less than the inputforce, a gain in distance occurs.

Figure 10 A First Class Lever

Input force

Examples of First Class Levers

Output force

Fulcrum

Load

Section

3

lever wheel and axleinclined plane pulleywedge compound

machine

Identify and give examples ofthe six types of simplemachines.

Analyze the mechanical advan-tage provided by each simplemachine.

Identify the simple machines thatmake up a compound machine.

screw



Second Class Levers With asecond class lever, the load isbetween the fulcrum and theinput force, as shown in Figure 11.Second class levers do not changethe direction of the input force,but they allow you to apply lessforce than the force exerted bythe load. Because the output forceis greater than the input force,you must exert the input forceover a greater distance. Someexamples of second class leversare shown at right.

Third Class Levers With athird class lever, the input forceis between the fulcrum and theload, as shown in Figure 12. Thirdclass levers do not change thedirection of the input force. Inaddition, they do not increase the input force. Therefore, theoutput force is always less than the input force. Some examplesof third class levers are shown at right.


Input force

Output force

Fulcrum

Examples of Second Class Levers

Using a second class leverresults in a mechanicaladvantage of greater than 1.The closer the load is to thefulcrum, the more the forceis increased and the greaterthe mechanical advantage.

Examples of Third Class Levers

Using a third class lever results in a mechanical advantageof less than 1 because force is decreased. But third classlevers are helpful because they increase the distancethrough which the output force is exerted.

Figure 11 A Second Class Lever

Output force

Input force

Fulcrum

Figure 12 A Third Class Lever

Load

Load

Inclined Planes Do you remember the story about how the Egyptians built theGreat Pyramid? One of the machines they used was the inclinedplane. An inclined plane is a simple machine that is a straight,slanted surface. A ramp is an example of an inclined plane.

Inclined planes can make work easier. Look at Figure 13.Using an inclined plane to load an upright piano into the backof a truck is easier than just lifting it into the truck. Rollingthe piano into the truck along an inclined plane requires asmaller input force than is required to lift the piano into thetruck. But remember that machines do not save work—there-fore, the input force must be exerted over a longer distance.

Mechanical Advantage of Inclined Planes The longer theinclined plane is compared with its height, the greater themechanical advantage. The mechanical advantage (MA) of aninclined plane can be calculated by dividing the length of theinclined plane by the height to which the load is lifted, asshown below:

Figure 13 The work you do on the piano to roll it up the rampis the same as the work you would do to lift it straight up. Aninclined plane simply allows you to apply a smaller force overa greater distance.


When Napoleon Bonaparte’sarmy invaded Egypt in 1798,one of his engineers report-edly calculated that thethree pyramids of Giza con-tained enough stone to builda wall about 2.5 m tall and0.3 m thick around theentire country of France.

MA 53 m0.6 m

3 m0.6 m

Compare work done with andwithout an inclined plane on

page 664 of the LabBook.


WedgesImagine trying to cut a watermelon in half with a spoon. Itwouldn’t be easy, would it? A knife is a much more usefulutensil for cutting because it’s a wedge. A wedge is a dou-ble inclined plane that moves. When you move a wedgethrough a distance, it applies a force on an object. Awedge applies an output force that is greater than yourinput force, but you apply the input force over a greaterdistance. The greater the distance you move the wedge,the greater the force it applies on the object. For exam-ple, the deeper you move a knife into a watermelon, asshown in Figure 14, the more force the knife applies to thetwo halves. Eventually, it pushes them apart. Other usefulwedges include doorstops, plows, axe heads, and chisels.

Mechanical Advantage of Wedges The longer and thin-ner the wedge is, the greater the mechanical advantage. That’swhy axes and knives cut better when you sharpen them—youare making the wedge thinner. Therefore, less input force isrequired. The mechanical advantage of a wedge can be deter-mined by dividing the length of the wedge by its greatestthickness, as shown below.

ScrewsA screw is an inclined plane that is wrappedin a spiral. When a screw is rotated, a smallforce is applied over the long distancealong the inclined plane of the screw.Meanwhile, the screw applies a large forcethrough the short distance it is pushed. Inother words, you apply a small input forceover a large distance, while the screwexerts a large output force over asmall distance. Screws are usedmost commonly as fasteners.Some examples of screws areshown in Figure 15.

201

MA 48 cm2 cm

8 cm

2 cm

Figure 15 When you turn a screw, you exert a small input force over a large turning distance,but the screw itself doesn’t movevery far.

Figure 14 Wedges, which areoften used to cut materials, allowyou to exert your force over anincreased distance.

Work and Machines

Mechanical Advantage of Screws If you could “unwind”the inclined plane of a screw, you would see that it is verylong and has a gentle slope. Recall that the longer an inclinedplane is compared with its height, the greater its mechanicaladvantage. Similarly, the longer the spiral on a screw is andthe closer together the threads, the greater the screw’s mechani-cal advantage, as shown in Figure 16.

1. Give an example of each of the following simplemachines: first class lever, second class lever, third classlever, inclined plane, wedge, and screw.

2. A third class lever has a mechanical advantage of lessthan 1. Explain why it is useful for some tasks.

3. Interpreting Graphics Look back at Figures 6, 7, and 8in Section 2. Identify the type of simple machine shownin each case. (If a lever is shown, identify its class.)

Wheel and AxleDid you know that when you turn a doorknob you are usinga machine? A doorknob is an example of a wheel and axle, asimple machine consisting of two circular objects of differentsizes. A wheel can be a crank, such as the handle on a fishing reel, or it can be a knob, such as a volume knob on

a radio. The axle is the smaller of the two circularobjects. Doorknobs, wrenches, ferris wheels,

screwdrivers, and steering wheels all use awheel and axle. Figure 17 shows how awheel and axle works.

Figure 16 The threads on thetop screw are closer togetherand wrap more times around, so that screw has a greatermechanical advantage than theone below it.

As the wheel turns, so does theaxle. But because the axle issmaller than the wheel, it rotatesthrough a smaller distance,which makes the output forcelarger than the input force.

REVIEW

b

When a small input force is applied to the wheel, itrotates through a circulardistance.

Figure 17How a Wheel and Axle Works


Wheel

Output force

Axle

a

Input force


Mechanical Advantage of a Wheeland Axle The mechanical advantageof a wheel and axle can be determinedby dividing the radius (the distancefrom the center to the edge) of thewheel by the radius of the axle, asshown at right. Turning the wheelresults in a mechanical advantage ofgreater than 1 because the radius ofthe wheel is larger than the radius ofthe axle.

PulleysWhen you open window blinds by pulling on a cord, you’reusing a pulley. A pulley is a simple machine consisting of agrooved wheel that holds a rope or a cable. A load is attachedto one end of the rope, and an input force is applied to theother end. There are two kinds of pulleys—fixed and movable.Fixed and movable pulleys can be combined to form a blockand tackle.

Fixed Pulleys Some pulleys onlychange the direction of a force.This kind of pulley is called a fixedpulley. Fixed pulleys do notincrease force. A fixed pulley isattached to something that doesnot move. By using a fixed pulley,you can pull down on the rope inorder to lift the load up. This isusually easier than trying to liftthe load straight up. Elevatorsmake use of fixed pulleys.

Movable Pulleys Unlike fixed pul-leys, movable pulleys are attachedto the object being moved. A mov-able pulley does not change aforce’s direction. Movable pulleysdo increase force, but you mustexert the input force over a greaterdistance than the load is moved.This is because you must makeboth sides of the rope move inorder to lift the load.


A fixed pulley only spins. Sothe distance through whichthe input force and the out-put force are exerted—andthus the forces themselves—are the same. Therefore, a fixed pulley provides amechanical advantage of 1.

A movable pulley moves upwith the load as it is lifted.Force is multiplied becausethe combined input force isexerted over twice the dis-tance of the output force. The mechanical advantage ofa movable pulley is the num-ber of rope segments thatsupport the load. In thisexample, the mechanicaladvantage is 2.

Inputforce Output

force

Inputforce

Outputforce

MA 515 cm3 cm

Radius of axle3 cm

Radius of wheel15 cm

Block and Tackles When a fixed pulley and a movable pul-ley are used together, the pulley system is called a block andtackle. A block and tackle can have a large mechanical advan-tage if several pulleys are used. A block and tackle used withina larger pulley system is shown in Figure 18.

Compound MachinesYou are surrounded by machines. As you saw earlier, you evenhave machines in your body! But most of the machines inyour world are compound machines, machines that are madeof two or more simple machines. You’ve already seen one exam-ple of a compound machine: a block and tackle. A block andtackle consists of two or more pulleys. On this page and thenext, you’ll see some other examples of compound machines.

Figure 18 The combination ofpulleys used by this crane allowsit to lift heavy pieces of scrapmetal.

Chapter 8204

The mechanical advantage ofthis block and tackle is 4because there are four ropesegments that support the load.This block and tackle multipliesyour input force four times, butyou have to pull the rope 4 mjust to lift the load 1 m.

Inputforce

Outputforce

Can Opener

Wheel and axle

The axle has gear teeth on itthat grip the can and act astiny levers to push the canalong when the axle turns.

Second class lever

Wedge

List five machines that youhave encountered today andindicate what type of machineeach is. Try to include at leastone compound machine andone machine that is part ofyour body.



Mechanical Efficiency of Compound Machines In gen-eral, the more moving parts a machine has, the lower itsmechanical efficiency. Thus the mechanical efficiency of com-pound machines is often quite low. For compound machinesthat involve many simple machines, such as automobiles andairplanes, it is very important that friction be reduced as muchas possible through the use of lubrication and other tech-niques. Too much friction could cause heating and damagethe simple machines involved, which could create safety prob-lems and could be expensive to repair.


Each arm of the scissorsis a first class lever.

Each sharpened edge ofthe scissors is a wedge.

Scissors Wheelchair

REVIEW

1. Give an example of a wheel and axle.

2. Identify the simple machines that make up tweezers andnail clippers.

3. Doing Calculations The radius of the wheel of a wheeland axle is four times greater than the radius of the axle.What is the mechanical advantage of this machine?

Zipper

Wheel and axle

Inside the metal clasp of this zipperare three wedges. One wedge opensthe zipper by splitting the teeth apart.Two other wedges close the zipper bypushing the teeth together.

NSTA

TOPIC: Simple Machines,Compound Machines


Chapter Highlights

Chapter 8206

SECTION 1 SECTION 2

Vocabularywork (p. 188)

joule (p. 190)

power (p. 191)

watt (p. 191)

Section Notes

• Work occurs when a forcecauses an object to move inthe direction of the force. Theunit for work is the joule (J).

• Work is done on an objectonly when a force makes anobject move and only whilethat force is applied.

• For work to be done on anobject, the direction of theobject’s motion must be inthe same direction as theforce applied.

• Work can be calculated bymultiplying force by distance.

• Power is the rate at whichwork is done. The unit forpower is the watt (W).

• Power can be calculated bydividing the amount of workby the time taken to do thatwork.

LabsA Powerful Workout (p. 662)

Vocabularymachine (p. 192)

work input (p. 193)

work output (p. 193)

mechanical advantage (p. 196)

mechanical efficiency (p. 197)

Section Notes

• A machine makes work easierby changing the size or direc-tion (or both) of a force.

• When a machine changesthe size of a force, thedistance through which theforce is exerted must alsochange. Force or distance canincrease, but not together.

Skills CheckMath ConceptsWORK AND POWER Suppose a woman raises a65 N object 1.6 m in 4 s. The work done andher power can be calculated as follows:

Visual UnderstandingMACHINES MAKE WORKEASIER A machine canchange the size or direction(or both) of a force. Reviewthe table on page 195 tolearn more about howmachines make work easier.

COMPOUND MACHINES A compound machineis made of two or more simple machines.Review the examples on pages 204 and 205.

W F d P Wt

65 N 1.6 m 1404

sJ

104 J 26 W


207Work and Machines

SECTION 3

• Mechanical advantage tellshow many times a machinemultiplies force. It can be cal-culated by dividing the out-put force by the input force.

• Mechanical efficiency is acomparison of a machine’swork output with workinput. Mechanical efficiencyis calculated by dividingwork output by work inputand is expressed as apercentage.

• Machines are not 100 per-cent efficient because someof the work done by amachine is used to overcomefriction. So work output isalways less than work input.

Vocabularylever (p. 198)

inclined plane (p. 200)

wedge (p. 201)

screw (p. 201)

wheel and axle (p. 202)

pulley (p. 203)

compound machine (p. 204)

Section Notes

• All machines are constructedfrom these six simplemachines: lever, inclinedplane, wedge, screw, wheeland axle, and pulley.

• Compound machines consistof two or more simplemachines.

• Compound machines havelow mechanical efficienciesbecause they have moremoving parts and thus morefriction to overcome.

LabsInclined to Move (p. 664)

Building Machines (p. 665)

Wheeling and Dealing (p. 666)

SECTION 2


TOPIC: Work and Power sciLINKS NUMBER: HSTP180

TOPIC: Mechanical Efficiency sciLINKS NUMBER: HSTP185

TOPIC: Simple Machines sciLINKS NUMBER: HSTP190

TOPIC: Compound Machines sciLINKS NUMBER: HSTP195



KEYWORD: HSTWRK




1. joule/watt

2. work output/work input

3. mechanical efficiency/mechanical advantage

4. screw/inclined plane

5. simple machine/compound machine


Multiple Choice

6. Work is being done when a. you apply a force to an object. b. an object is moving after you apply a

force to it.c. you exert a force that moves an object

in the direction of the force. d. you do something that is difficult.

7. The work output for a machine is alwaysless than the work input because a. all machines have a mechanical

advantage. b. some of the work done is used to

overcome friction.c. some of the work done is used

to overcome distance.d. power is the rate at which

work is done.

8. The unit for work is the a. joule. c. newton. b. joule per second. d. watt.

208

9. Which of the following is not a simple machine?a. a faucet handleb. a jar lidc. a can openerd. a seesaw

10. Power isa. how strong someone or something is. b. how much force is being used. c. how much work is being done.d. how fast work is being done.

11. The unit for power is thea. newton. c. watt.b. kilogram. d. joule.

12. A machine can increasea. distance at the expense of force. b. force at the expense of distance. c. neither distance nor force.d. Both (a) and (b)

Short Answer

13. Identify the simple machines that makeup a pair of scissors.

14. In two or three sentences, explain theforce-distance trade-off that occurs when amachine is used to make work easier.

15. Explain why you do work ona bag of groceries when youpick it up but not when youare carrying it.


Concept Mapping

16. Create a concept mapusing the followingterms: work, force,distance, machine,mechanicaladvantage.


17. Why do you think levers usually have agreater mechanical efficiency than othersimple machines do?

18. The winding road shown below is actuallya series of inclined planes. Describe how awinding road makes it easier for vehiclesto travel up a hill.

19. Why do you think you would not want toreduce the friction involved in using awinding road?

MATH IN SCIENCE

20. You and a friend together apply a force of1,000 N to a 3,000 N automobile to makeit roll 10 m in 1 minute and 40 seconds. a. How much work did you and your

friend do together? b. What was your combined power?


For each of the images below, identify theclass of lever used and calculate the mechani-cal advantage.

21.

22.

Fulcrum

Input force40 N

Output force120 N

FulcrumOutput force

4 N

Input force20 N




ReadingCheck-up


210

Micromachines

The technology of mak-ing things smaller andsmaller keeps growing

and growing. Powerful com-puters can now be held in thepalm of your hand. But whatabout motors smaller than agrain of pepper? Or gnat-sizedrobots that can swim throughthe bloodstream? These arejust a couple of the possibili-ties for micromachines.

Microscopic MotorsResearchers have already builtgears, motors, and otherdevices so small that youcould accidentally inhale one!For example, one engineer devised a motor sosmall that five of the motors would fit on theperiod at the end of this sentence. This micro-motor is powered by static electricity instead ofelectric current, and the motor spins at 15,000revolutions per minute. This is about twice asfast as most automobile engines running at top speed.

Small SensorsSo far micromachines have been most useful assensing devices. Micromechanical sensors canbe used in places too small for ordinary instru-ments. For example, blood-pressure sensors canfit inside blood vessels and can detect minutechanges in a person’s blood pressure. Each sen-sor has a patch so thin that it bends when thepressure changes.

Cell-Sized RobotsSome scientists are investigating the possibilityof creating cell-sized machines called nanobots.These tiny robots may have many uses in medi-cine. For instance, if nanobots could be injected

into a person’s bloodstream,they might be used to destroydisease-causing organismssuch as viruses and bacteria.Nanobots might also be usedto count blood cells or todeliver medicine.

The ultimate in micro-machines would be machinescreated from individual atomsand molecules. Althoughthese machines do not cur-rently exist, scientists arealready able to manipulatesingle atoms and molecules.For example, the “molecularman” shown below is madeof individual molecules. These

molecules are moved by using a scanning tun-neling microscope.

A Nanobot’s “Life” Imagine that you are ananobot traveling througha person’s body. Whattypes of things do youthink you would see?What type of work couldyou do? Write a story thatdescribes what your ex-periences as a nanobotmight be like.

The earliest workingmicromachine had aturning central rotor.

“Molecular man” is composed of 28carbon monoxidemolecules.


211

Wheelchair Innovators

Two recent inventions have dramaticallyimproved the technology of wheelchairs.With these new inventions, some wheel-

chair riders can now control their chairs withvoice commands and others can take a cruiseover a sandy beach.

Voice-Command WheelchairAt age 27, Martine Kemph invented a voice-recognition system that enables people withoutarms or legs to use spoken commands to oper-ate their motorized wheelchairs. Here's how itworks: The voice-recognition computer trans-lates spoken words into digital commands,which are then directed to electric motors.These commands completely control the operating speed and direction of the motors,giving the operator total control over the chair’smovement.

Kemph’s system can execute spoken com-mands almost instantly. In addition, the systemis easy to program, so each user can tailor thecomputer’s list of commands to his or herneeds.

Kemph named the computer Katalvox, usingthe root words katal, which is Greek for “tounderstand,” and vox, which is Latin for “voice.”

The Surf ChairMike Hensler was a lifeguard at Daytona Beach,Florida, when he realized that it was next toimpossible for someone in a wheelchair tocome onto the beach. Although he had neverinvented a machine before, Hensler decided tobuild a wheelchair that could be maneuveredacross sand without getting stuck. He beganspending many evenings in his driveway with apile of lawn-chair parts, designing the chair bytrial and error.

The result of Hensler’s efforts looks very dif-ferent from a conventional wheelchair. With hugerubber wheels and a thick frame of white PVC

pipe, the Surf Chair not only moves easily oversandy terrain but also is weather resistant andeasy to clean. The newest models of the SurfChair come with optional attachments, such as a variety of umbrellas, detachable armrests and footrests, and evenplaces to attachfishing rods.

Design One Yourself Can you think of any other ways to improvewheelchairs? Think about it, and put your ideasdown on paper. To inspire creative thinking,consider how a wheelchair could be madelighter, faster, safer, or easier to maneuver.

Mike Hensler tries out his Surf Chair.


212 Chapter 9

What Is Energy? . . . . 214MathBreak . . . . . . . . . 217QuickLab . . . . . . . . . . 220Internet Connect . . . . 221

Energy Conversions . . 222Apply . . . . . . . . . . . . . 224Internet Connect . . . . 225

Conservation of Energy . . . . . . . . . 229Biology Connection . . 231Internet Connect . . . . 231

Energy Resources . . . 232

Chapter Review . . . . . . . . . 240


LabBook . . . . . . . . . . . 668–671

Energy andEnergyResources

Energy andEnergyResources

The Race Is On!Imagine that you’re a driver in this race. Your car will needa lot of energy to finish, so you should make sure your caris fueled up and ready. You’ll probably need a lot of gaso-line, right? Nope, just a lot of sunshine! The car in thisphoto is solar powered—energy from the sun makes it go.In this chapter, you’ll learn about different types of energy.You’ll also learn where the energy that runs our cars andour appliances comes from.


1. What is energy?2. How is energy converted

from one form toanother?

3. What is an energyresource?


213

ENERGY SWINGS! All matter has energy. But what is energy? In this activity, you’llobserve a moving pendulum tolearn about energy.

Procedure

1. Make a pendulum by tying a15 cm long string around thehook of the 100 g hooked mass.

2. Hold the string with one hand. Pullthe mass slightly to the side, andlet go of the mass without pushingit. Watch at least 10 swings of thependulum.

3. In your ScienceLog, record yourobservations. Be sure to note howfast and how high the pendulumswings.

4. Repeat step 2, but pull the massfarther to the side.

5. Record your observations, notinghow fast and how high the pendu-lum swings.

Analysis

6. Do you think the pendulum hasenergy? Explain your answer.

7. What causes the pendulum tomove?

8. Do you think the pendulum hasenergy before you let go of themass? Explain your answer.

Energy and Energy ResourcesCopyright © by Holt, Rinehart and Winston. All rights reserved.


Figure 1 When one object does workon another, energy is transferred.

Chapter 9214

a

b

c

What Is Energy?It’s match point. The crowd is dead silent. The tennis playersteps up to serve. With a look of determination, she bouncesthe tennis ball several times. Next, in one fluid movement,she tosses the ball into the air and then slams it with herracket. The ball flies toward her opponent, who steps up andswings her racket at the ball. Suddenly, THWOOSH!! The ballgoes into the net, and the net wiggles from the impact. Game,set, and match!!

Energy and Work—Working TogetherEnergy is around you all the time. So what is it exactly? Inscience, you can think of energy as the ability to do work.Work occurs when a force causes an object to move in thedirection of the force. How are energy and work involved inplaying tennis? In this example, the tennis player does workon her racket, the racket does work on the ball, and the balldoes work on the net. Each time work is done, something isgiven by one object to another that allows it to do work. That“something” is energy. As you can see in Figure 1, work is atransfer of energy.

Because work and energy are so closely related, they areexpressed in the same units—joules ( J). When a given amountof work is done, the same amount of energy is involved.

When the racket does workon the ball, the ball gainsthe ability to do work onsomething else. Energy istransferred from the racketto the ball.

When she does work on theracket, the racket gains theability to do work on theball. Energy is transferredfrom the tennis player tothe racket.

The tennis player cando work on her racketbecause she has energy.

Section

1

energykinetic energypotential energymechanical energy

Explain the relationship betweenenergy and work.

Compare kinetic and potentialenergy.

Summarize the different formsof energy.


Energy and Energy Resources 215

Figure 3 The red car has morekinetic energy than the green carbecause the red car is movingfaster. But the truck has morekinetic energy than the red car because the truck is moremassive.

25 m/s

25 m/s

Figure 2 When you swing ahammer, you give it kineticenergy, which it uses to do work on the nail.

20 m/s

Kinetic Energy Is Energy of MotionFrom the tennis example on the previous page, you learnedthat energy is transferred from the racket to the ball. As theball flies over the net, it has kinetic (ki NET ik) energy, theenergy of motion. All moving objects have kinetic energy. Doesthe tennis player have kinetic energy? Definitely! She has kineticenergy when she steps up to serve and when she swings theracket. When she’s standing still, she doesn’t have any kineticenergy. However, the parts of her body that are moving—hereyes, her heart, and her lungs—do have some kinetic energy.

Objects with kinetic energy can do work. If you’ve evergone bowling, you’ve done work using kinetic energy. Whenyou throw the ball down the lane, you do work on it, trans-ferring your kinetic energy to the ball. As a result, the bowl-ing ball can do work on the pins. Another example of doingwork with kinetic energy is shown in Figure 2.

Kinetic Energy Depends on Speed and Mass An object’skinetic energy can be determined with the following equation:

Kinetic energy

In this equation, m stands for an object’s mass, and v standsfor an object’s speed. The faster something is moving, the morekinetic energy it has. In addition, the more massive a movingobject is, the more kinetic energy it has. But which do youthink has more of an effect on an object’s kinetic energy, itsmass or its speed? As you can see from the equation, speed issquared, so speed has a greater effect on kinetic energy thandoes mass. You can see an example of how kinetic energydepends on speed and mass in Figure 3.

mv2

2


Potential Energy Is Energy of PositionNot all energy involves motion. Potential energy is the energyan object has because of its position or shape. For example,the stretched bow shown in Figure 4 has potential energy. Thebow is not moving, but it has energy because work has beendone to change its shape. A similar example of potential energyis in a stretched rubber band.

Gravitational Potential Energy Depends on Weight andHeight When you lift an object, you do work on it by usinga force that opposes gravitational force. As a result, you givethat object gravitational potential energy. Books on a bookshelfhave gravitational potential energy, as does your backpack afteryou lift it onto your back. As you can see in Figure 5, theamount of gravitational potential energy an object has dependson its weight and its distance above Earth’s surface.

Figure 4 The stored potentialenergy of the bow and stringallows them to do work on thearrow when the string is released.

Chapter 9216

The diver on the higher platform has moregravitational potential energy than the diver on the lower platform. The diver on the higherplatform did more work to climb up to theplatform.

450 N 500 N

550 N

550 N

Figure 5 Weight and Height Affect Gravitational Potential Energy

The diver on the left weighs less and thereforehas less gravitational potential energy than thediver on the right. The diver on the left did lesswork to climb up the platform.

a b


Figure 6 As a pin is juggled, itsmechanical energy is the sum ofits potential energy and its kineticenergy at any point.

217

Calculating Energy1. What is the kinetic energy

of a 4,000 kg elephant run-ning at 3 m/s? at 4 m/s?

2. If you lift a 50 N water-melon to the top of a 2 mrefrigerator, how muchgravitational potentialenergy do you give thewatermelon?

MATH BREAK

1. How are energy and work related?

2. What is the difference between kinetic and potentialenergy?

3. Applying Concepts Explain why a high-speed collisionmight cause more damage to vehicles than a low-speedcollision.

REVIEW

Energy and Energy Resources

Calculating Gravitational Potential Energy You can cal-culate gravitational potential energy by using the followingequation:

Gravitational potential energy weight height

Because weight is expressed in newtons and height is expressedin meters, gravitational potential energy is expressed in newton-meters (N•m), or joules ( J). So a 25 N object at a height of 3 m has 25 N 3 m 75 J of gravitational potential energy.

Recall that work force distance. Weight is the amountof force you must exert on an object in order to lift it, andheight is a distance. So calculating an object’s gravitational poten-tial energy is done by calculating the amount of work done onthe object to lift it to a given height. You can practice calcu-lating gravitational potential energy as well as kinetic energy inthe MathBreak at right.

Mechanical Energy Sums It All UpHow would you describe the energy of the juggler’s pins inFigure 6? Well, to describe their total energy, you woulddescribe their mechanical energy. Mechanical energy is thetotal energy of motion and position of an object. Mechanicalenergy can be all potential energy, all kinetic energy, or someof both. The following equation defines mechanical energyas the sum of kinetic and potential energy:

Mechanical energy potential energy kinetic energy

When potential energy increases (or decreases), kineticenergy has to decrease (or increase) in order for mechanicalenergy to remain constant. So the amount of an object’s kineticor potential energy may change, but its mechanical energyremains the same. You’ll learn more about these changes inthe next section.


Forms of EnergyAll energy involves either motion or position. But energy takesdifferent forms. These forms of energy include thermal, chemi-cal, electrical, sound, light, and nuclear energy. In the nextfew pages, you will learn how the different forms of energyrelate to kinetic and potential energy.

Thermal Energy All matter is made of particles that are con-stantly in motion. Because the particles are in motion, theyhave kinetic energy. The particles also have energy because ofhow they are arranged. Thermal energy is the total energy ofthe particles that make up an object. At higher temperatures,particles move faster. The faster the particles move, the morekinetic energy they have and the greater the object’s thermalenergy is. In addition, particles of a substance that are fartherapart have more energy than particles of the same substancethat are closer together. Look at Figure 7. Thermal energy alsodepends on the number of particles in a substance.

Chemical Energy What is the source of the energy in food?Food consists of chemical compounds. When compounds,such as the sugar in some foods, are formed, work is done tojoin, or bond, the different atoms together to form molecules.Chemical energy is the energy of a compound that changes asits atoms are rearranged to form new compounds. Chemicalenergy is a form of potential energy. Some molecules thathave many atoms bonded together, such as gasoline, have alot of chemical energy. In Figure 8 on the next page, you cansee an example of chemical energy.

Chapter 9218

Figure 7 The particles in steamhave more energy than the parti-cles in ice or ocean water. Butthe ocean has the most thermalenergy because it has the mostparticles.

NGP

The particles in an ice cubevibrate in fixed positions andtherefore do not have a lot ofenergy.

The particles in ocean water arenot in fixed positions and can movearound. They have more energythan the particles in an ice cube.

The particles in steam are farapart. They move rapidly, so theyhave more energy than the parti-cles in ocean water.


Electrical Energy The electrical outlets in your home allowyou to use electrical energy. Electrical energy is the energy ofmoving electrons. Electrons are the negatively charged parti-cles of atoms. An atom is the smallest particle into which anelement can be divided.

Suppose you plug an electrical device, such as the portablestereo shown in Figure 9, into an outlet and turn it on. Theelectrons in the wires will move back and forth, changingdirections 120 times per second. As they do, energy is trans-ferred to different parts within the stereo. The electrical energycreated by moving electrons is used to dowork. The work of a stereo is to producesound.

The electrical energy available to yourhome is produced at power plants. Hugegenerators rotate magnets within coils ofwire to produce electrical energy. Becausethe electrical energy results from thechanging position of the magnet, electri-cal energy can be considered a form ofpotential energy. As soon as a device isplugged into an outlet and turned on,electrons move back and forth within thewires of the cord and within parts of thedevice. So electrical energy can also beconsidered a form of kinetic energy.


Figure 8 Examples of Chemical Energy

Figure 9 The movement ofelectrons produces the electricalenergy that a stereo uses toproduce sound.

When wood is burned, thechemical energy stored in thewood is used to toast yourmarshmallows.

When you eat a marshmallow, chemicalenergy stored in the sugar becomesavailable for you to use.

Chemical energy is stored in themarshmallow’s sugar molecules.


Sound Energy You probably know that your vocal cordsdetermine the sound of your voice. When you speak, airpasses through your vocal cords, making them vibrate,or move back and forth. Sound energy is caused by anobject’s vibrations. Figure 10 describes how a vibratingobject transmits energy through the air around it.

Sound energy is a form of potential and kineticenergy. To make an object vibrate, work must be done

to change its position. For example, when you pluck aguitar string, you stretch it and release it. The stretching

changes the string’s position. As a result, the string storespotential energy. In the release, the string uses its potentialenergy to move back to its original position. The movingguitar string has kinetic energy, which the string uses to dowork on the air particles around it. The air particles vibrateand transmit this kinetic energy from particle to particle.When the vibrating air particles cause your eardrum tovibrate, you hear the sound of the guitar.

Light Energy Light allows us to see, but did you know thatnot all light can be seen? Figure 11 shows a type of lightthat we use but can’t see. Light energy is produced by thevibrations of electrically charged particles. Like sound vibra-tions, light vibrations cause energy to be transmitted. Butunlike sound, the vibrations that transmit light energy don’tcause other particles to vibrate. In fact, light energy can betransmitted through a vacuum (the absence of matter).

Chapter 9220

Figure 11 The energy used to cook foodin a microwave is a form of light energy.

Figure 10 As the guitar stringsvibrate, they cause particles inthe air to vibrate. These vibra-tions transmit energy.

Hear That Energy!

1. Make a simple drum bycovering the open end ofan empty coffee can withwax paper. Secure the waxpaper with a rubber band.

2. Using the eraser end of apencil, tap lightly on thewax paper. In yourScienceLog, describe howthe paper responds. Whatdo you hear?

3. Repeat step 2, but tap thepaper a bit harder. In yourScienceLog, compare yourresults with those of step 2.

4. Cover half of the wax paperwith one hand. Now tapthe paper. What happened?How can you describesound energy as a form ofmechanical energy?


Nuclear Energy What form of energy can come from a tinyamount of matter, can be used to generate electrical energy,and gives the sun its energy? It’s nuclear (NOO klee uhr)energy, the energy associated with changes in the nucleus(NOO klee uhs) of an atom. Nuclear energy is producedin two ways—when two or more nuclei (NOO klee IE)join together or when the nucleus of an atom splits apart.

In the sun, shown in Figure 12, hydrogen nuclei jointogether to make a larger helium nucleus. This reactionreleases a huge amount of energy, which allows the sunto light and heat the Earth.

The nuclei of some atoms, such as uranium, store a lotof potential energy. When work is done to split these nucleiapart, that energy is released. This type of nuclear energy isused to generate electrical energy at nuclear power plants,such as the one shown in Figure 13.


Figure 13 In a nuclear powerplant, small amounts of mattercan produce large amounts of nuclear energy.

1. What determines an object’s thermal energy?

2. Describe why chemical energy is a form of potential energy.

3. Explain how sound energy is produced when you beat adrum.

4. Analyzing Relationships When you hit a nail into aboard using a hammer, the head of the nail gets warm.In terms of kinetic and thermal energy, describe whyyou think this happens.

REVIEW

Figure 12 Without the nuclearenergy from the sun, life onEarth would not be possible.

NSTA

TOPIC: What Is Energy?,Forms of Energy



When you jumpdown, your kineticenergy is convertedinto the potentialenergy of thestretched trampoline.

Right before you hitthe trampoline, all ofyour potential energyhas been convertedback into kineticenergy.

The trampoline’spotential energy isconverted into kineticenergy, which is trans-ferred to you, makingyou bounce up.

At the top of yourjump, all of yourkinetic energy hasbeen converted intopotential energy.

Chapter 9222

Energy ConversionsWhen you use a hammer to pound a nail into a board, youtransfer your kinetic energy to the hammer, and the hammertransfers that kinetic energy to the nail. But energy is involvedin other ways too. For example, sound energy is producedwhen you hit the nail. An energy transfer often leads to anenergy conversion, a change from one form of energy intoanother. Any form of energy can be converted into any otherform of energy, and often one form of energy is convertedinto more than one other form. In this section, you’ll learnhow energy conversions make your daily activities possible.

From Kinetic to Potential and BackTake a look at Figure 14. Have you ever jumped on a tram-poline? What types of energy are involved in this bouncingactivity? Because you’re moving when you jump, you havekinetic energy. And each time you jump into the air, youchange your position with respect to the ground, so you alsohave gravitational potential energy. Another kind of potentialenergy is involved too—that of the trampoline stretching whenyou jump on it.

Figure 14 Kinetic and potentialenergy are converted back andforth as you jump up and downon a trampoline.

1 2 3 4

Section

2

energy conversion

Describe an energy conversion. Give examples of energy

conversions among the differentforms of energy.

Explain the role of machines inenergy conversions.

Explain how energy conversionsmake energy useful.


Another example of the energy conversionsbetween kinetic and potential energy is themotion of a pendulum (PEN dyoo luhm). Shownin Figure 15, a pendulum is a mass hung froma fixed point so that it can swing freely. Whenyou lift the pendulum to one side, you do workon it, and the energy used to do that work isstored by the pendulum as potential energy. Assoon as you let the pendulum go, it swingsbecause the Earth exerts a force on it. The workthe Earth does converts the pendulum’s poten-tial energy into kinetic energy.

Conversions Involving Chemical EnergyYou’ve probably heard the expression “Breakfast is the mostimportant meal of the day.” What does this statement mean?Why does eating breakfast help you start the day? As your bodydigests food, chemical energy is released and is available toyou, as discussed in Figure 16.


Self-CheckAt what point does a roller coasterhave the greatest potential energy?the greatest kinetic energy? (Seepage 724 to check your answer.)

Chemical energy of foodis converted into . . .

Figure 15 A pendulum’s mechanical energy is all kinetic (KE) at the bottom of its swing and all potential (PE) at the top of its swing.

Figure 16 Your body performs energy conversions.

KE increasingPE decreasing

PE increasingKE decreasing

KE = 0 KE = 0

PE = 0

. . . kinetic energy when you are active and thermal energy to

maintain body temperature.


Camping with EnergyIf you go camping, you probably use a stove,such as the one shown here, to preparemeals. Describe some of the energy conver-sions that take place when lighting thestove, cooking the food, eating the preparedmeal, and then setting out on a long hike.

Would you believe that the chemical energy in the foodyou eat is a result of the sun’s energy? It’s true! When you eatfruits, vegetables, grains, or meat from animals that ate fruits,vegetables, or grains, you are taking in chemical energy thatresulted from a chemical change involving the sun’s energy. Asshown in Figure 17, photosynthesis (FOHT oh SIN thuh sis) useslight energy to produce new substances with chemical energy.In this way light energy is converted into chemical energy.

Chapter 9224

Light energy

Carbon dioxidein the air

Water in the soil

Chlorophyll ingreen leaves

Sugar in food

Photosynthesis

light energy+ water sugar + oxygen

chlorophyll

carbon dioxide

Figure 17 Green plants use chlorophyll and lightenergy from the sun to produce the chemicalenergy in the food you eat.


Conversions Involving Electrical EnergyYou use electrical energy all the time—when you listen to theradio, when you make toast, and when you take a picture witha camera. Electrical energy can be easily converted into otherforms of energy. Figure 18 shows how electrical energy is con-verted in a hair dryer.


Figure 18 Energy Conversions in a Hair Dryer

1. What is an energy conversion?

2. Describe an example in which electrical energy is con-verted into thermal energy.

3. Describe an energy conversion involving chemical energy.

4. Applying Concepts Describe the kinetic-potential energyconversions that occur when you bounce a basketball.

1

2

3

REVIEW

Alarm clock electrical energy light energy and sound energy

Battery chemical energy electrical energy

Light bulb electrical energy light energy and thermal energy

Blender electrical energy kinetic energy and sound energy

Electrical energyenters the hairdryer and is con-verted into kineticenergy as a smallelectric motorspins a fan blade.

Electrical energy is alsoconverted into thermalenergy in a grid ofwires that heats up.

The fan forces air acrossthe hot wires, and hot airblows out the nozzle ofthe hair dryer. You canhear the sound energythat is also produced.

Examples of Conversions Involving Electrical Energy

NSTA

TOPIC: Energy ConversionsGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP215


Energy and Machines You’ve been learning about energy, its differentforms, and how it can undergo conversions.Another way to learn about energy is to look athow machines use energy. A machine can makework easier by changing the size or direction (orboth) of the force required to do the work.Suppose you want to crack open a walnut. Using

a nutcracker, like the one shown in Figure 19,would be much easier (and less painful) than using

your fingers. You transfer your energy to the nutcracker,and it transfers energy to the nut. But the nutcracker will

not transfer more energy to the nut than you transfer to thenutcracker. In addition, some of the energy you transfer toa machine can be converted by the machine into other formsof energy. Another example of how energy is used by amachine is shown in Figure 20.

Chapter 9226

Figure 20 To start and keepyour bike moving, energy mustbe converted and transferred.

Figure 19 Some of the kineticenergy you transfer to a nut-cracker is converted into soundenergy as the nutcracker trans-fers energy to the nut.

2

34

Chemical energy in your bodyis converted into kinetic energywhen your muscle fibers con-tract and relax.

Your legs transfer this kineticenergy to the pedals, pushingthem around in a circle.

The pedals transfer this kineticenergy to the gear wheel, whichtransfers kinetic energy to the chain.

The chain moves and transfersenergy to the back wheel,which gets you moving!

1


Machines Are Energy Converters As you saw in the exam-ples on the previous page, when machines transfer energy,energy conversions can often result. For example, you canhear the sounds that your bike makes when you pedal it,change gears, or brake swiftly. That means that some of thekinetic energy being transferred gets converted into soundenergy as the bike moves. Some machines are especially use-ful because they are energy converters. Figure 21 shows anexample of a machine specifically designed to convert energyfrom one form to another. In addition, the chart at right listsother machines that perform useful energy conversions.

electric motor

windmill

doorbell

gas heater

telephone


Figure 21 The continuous conversion of chemical energy intothermal energy and kinetic energy in a car’s engine is necessaryto make a car move.

Some Machines that Convert Energy

A mixture of gasolineand air enters theengine as the pistonmoves downward.

Piston

The kinetic energy ofthe crankshaft raises thepiston, and the gasolinemixture is forced uptoward the spark plug,which uses electricalenergy to ignite thegasoline mixture.

Spark plug

Crankshaft

As the gasoline mix-ture burns, chemicalenergy is convertedinto thermal energyand kinetic energy,forcing the pistonback down.

The kinetic energyof the crankshaftforces the pistonup again, pushingexhaust gases out.Then the cyclerepeats.

1 2

3 4

microphone

toaster

dishwasher

lawn mower

clock


Why Energy Conversions Are ImportantEverything we do is related to energy conversions. Heatingour homes, obtaining energy from a meal, growing plants,and many other activities all require energy conversions.

Making Energy Useful You can think of energy con-versions as a way of getting energy in the form that youneed. Machines help harness existing energy and makethat energy work for you. Did you know that the windcould help you cook a meal? A wind turbine, shown inFigure 22, can perform an energy conversion that wouldallow you to use an electric stove to do just that.

Making Conversions Efficient You may have heard that a car may be considered energy efficient if it gets good gas mileage, and your home may be energy efficientif it is well insulated. In terms of energy conversions,energy efficiency (e FISH uhn see) is a comparison of theamount of energy before a conversion with the amountof useful energy after a conversion. For example, the energyefficiency of a light bulb would be a comparison of the electrical energy going into it with the light energycoming out of it. The less electrical energy that is con-verted into thermal energy instead of into light energy,the more efficient the bulb.

Not all of the energy in a conversion becomes usefulenergy. Just as work input is always greater than work output, energy input is also always greater than energyoutput. But the closer the energy output is to the energyinput, the more efficient the conversion is. Making energyconversions more efficient is important because greaterefficiency means less waste.

Chapter 9228

1. What is the role of machines in energy conversions?

2. Give an example of a machine that is an energy con-verter, and explain how the machine converts oneform of energy to another.

3. Applying Concepts A car that brakes suddenly comesto a screeching halt. Is the sound energy producedin this conversion a useful form of energy? Explainyour answer.

REVIEW

Figure 22 In a wind turbine, thekinetic energy of the wind canbe collected and converted intoelectrical energy.

Turn to page 242 to find out aboutbuildings that are energy efficient aswell as environmentally friendly.


Figure 23 Due to friction,not all of the cars’ potentialenergy (PE) is converted intokinetic energy (KE) as thecars go down the first hill. Inaddition, not all of the cars’kinetic energy is convertedinto potential energy as thecars go up the second hill.

229

Conservation of EnergyMany roller coasters have a mechanism that pulls the cars upto the top of the first hill, but the cars are on their own therest of the ride. As the cars go up and down the hills on thetrack, their potential energy is converted into kinetic energyand back again. But the cars never return to the same heightthey started from. Does that mean that energy gets lost some-where along the way? Nope—it just gets converted into otherforms of energy.

Where Does the Energy Go? In order to find out where a roller coaster’s original potentialenergy goes, you have to consider more than just the hills ofthe roller coaster. You have to consider friction too. Friction isa force that opposes motion between two surfaces that aretouching. For the roller coaster to move, work must be doneto overcome the friction between the cars’ wheels and thecoaster track and between the cars and the surrounding air.The energy used to do this work comes from the originalamount of potential energy that the cars have on the top ofthe first hill. The need to overcome friction affects the designof a roller coaster track. In Figure 23, you can see that the sec-ond hill will always be shorter than the first.

When energy is used to overcome friction, some of theenergy is converted into thermal energy. Some of the cars’potential energy is converted into thermal energy on the waydown the first hill, and then some of their kinetic energy isconverted into thermal energy on the way up the second hill.So energy isn’t lost at all—it just undergoes a conversion.

a

b

c

PE is greatest at thetop of the first hill.

KE at the bottom of thefirst hill is less than thePE was at the top.

PE on top of the secondhill is less than KE andPE from the first hill.

Section

3

frictionlaw of conservation of energy

Explain how energy is conservedwithin a closed system.

Explain the law of conservationof energy.

Give examples of how thermalenergy is always a result ofenergy conversion.

Explain why perpetual motion isimpossible.


Energy Is Conserved Within a Closed SystemA closed system is a well-defined group of objects that transferenergy between one another. For example, a closed system thatinvolves a roller coaster consists of the track, the cars, and thesurrounding air. On a roller coaster, some mechanical energy(the sum of kinetic and potential energy) is always convertedinto thermal energy because of friction. Sound energy is alsoa result of the energy conversions in a roller coaster. You canunderstand that energy is not lost on a roller coaster onlywhen you consider all of the factors involved in a closed sys-tem. If you add together the cars’ kinetic energy at the bot-tom of the first hill, the thermal energy due to overcomingfriction, and the sound energy produced, you end up with thesame total amount of energy as the original amount of poten-tial energy. In other words, energy is conserved.

Law of Conservation of Energy No situation has been foundwhere energy is not conserved. Because this phenomenon isalways observed during energy conversions, it is described asa law. According to the law of conservation of energy, energycan be neither created nor destroyed. The total amount ofenergy in a closed system is always the same. Energy can bechanged from one form to another, but all the different formsof energy in a system always add up to the same total amountof energy, no matter how many energy conversions occur.

Consider the energy conversions ina light bulb, shown in Figure 24. Youcan define the closed system to includethe outlet, the wires, and the parts of

the bulb. While not all of the origi-nal electrical energy is converted

into light energy, no energy is lost.At any point during its use, thetotal amount of electrical energyentering the light bulb is equalto the total amount of light andthermal energy that leaves the

bulb. Energy is conserved.

Chapter 9230

Some energy is convertedto thermal energy, whichmakes the bulb feel warm.

Some electrical energy isconverted into light energy.

Some electrical energy is con-verted into thermal energybecause of friction in the wire.

Figure 24 Energy Conservation in a Light Bulb

Try to keep an egg from breaking while learning moreabout the law of conservation

of energy on page 671 in the LabBook.



No Conversion Without Thermal EnergyAny time one form of energy is converted into another form,some of the original energy always gets converted into thermalenergy. The thermal energy due to friction that results fromenergy conversions is not useful energy. That is, this thermalenergy is not used to do work. Think about a car. You put gasinto a car, but not all of the gasoline’s chemical energy makesthe car move. Some waste thermal energy will always resultfrom the energy conversions. Much of this waste thermal energyexits a car engine through the radiator and the exhaust pipe.

Perpetual Motion? No Way! People have dreamed of con-structing a machine that runs forever without any additionalenergy—a perpetual (puhr PECH oo uhl) motion machine. Such a machine would put out exactly as much energy as it takes in. But because some wastethermal energy always resultsfrom energy conversions, per-petual motion is impossible. The only way a machine cankeep moving is to have a con-tinuous supply of energy. Forexample, the “drinking bird”shown in Figure 25 continuallyuses thermal energy from theair to evaporate the water fromits head. So it is not a perpet-ual motion machine.


1. Describe the energy conversions that take place in apendulum, and explain how energy is conserved.

2. Why is perpetual motion impossible?

3. Analyzing Viewpoints Imagine that you drop a ball. Itbounces a few times, but then it stops. Your friend saysthat the ball has lost all of its energy. Using what youknow about the law of conservation of energy, respondto your friend’s statement.

REVIEW

When the bird “drinks,” thefelt covering its head gets wet.

When the bird is upright, waterevaporates from the felt,decreasing the temperatureand pressure in the head. Fluid is drawn up from the tail, where pressure is higher, and the bird tips.

a

b


Whenever you do work, you usechemical energy stored in your bodythat comes from food you’ve eaten.As you do work, some of that chemi-cal energy is always converted intothermal energy. That’s why yourbody heats up after performing a task, such as raking leaves, forseveral minutes.

After the bird “drinks,”fluid returns to the tail,the bird flips upright,and the cycle repeats.

c

Figure 25 The “Drinking Bird”

NSTA

TOPIC: Law of Conservation of EnergyGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP217

Chapter 9232

Energy ResourcesEnergy is used to light and warm our homes; to produce food,clothing, and other products; and to transport people and prod-ucts from place to place. Where does all this energy comefrom? An energy resource is a natural resource that can beconverted by humans into other forms of energy in order todo useful work. In this section, you will learn about severalenergy resources, including the resource responsible for mostother energy resources—the sun.

Nonrenewable ResourcesSome energy resources, called nonrenewable resources, cannotbe replaced after they are used or can be replaced only overthousands or millions of years. Fossil fuels are the most impor-tant nonrenewable resources.

Fossil Fuels Coal, petroleum, and natural gas,shown in Figure 26, are the most common fossil fuels.Fossil fuels are energy resources that formed from theburied remains of plants and animals that lived mil-lions of years ago. These plants stored energy fromthe sun by photosynthesis. Animals used and storedthis energy by eating the plants or by eating animalsthat ate plants. So fossil fuels are concentrated formsof the sun’s energy.

Natural gas wasformed much in thesame way that petro-leum was formed,and it is often foundalong with petroleumdeposits.Petroleum, or oil, was formed

from organisms that lived inprehistoric lakes and seas.Crushed by layers of sedimentand heated by the Earth, theremains were slowly changedinto petroleum.

Figure 26 Formation of Fossil Fuels

This piece of coal containing a fern fossil shows that coalformed from plants that livedmillions of years ago.

Section

4

energy resourcenonrenewable resourcesfossil fuelsrenewable resources

Name several energy resources. Explain how the sun is the source

of most energy on Earth. Evaluate the advantages and

disadvantages of using variousenergy resources.



Now, millions of years later, energy from the sun is releasedwhen fossil fuels are burned. Any fossil fuel contains storedenergy from the sun that can be converted into other types ofenergy. The information below shows how important fossilfuels are to our society.


Coal exports

Industrialuses

Coal usedin the making

of steel

Heating

Coal Use (U.S.)

Electricpower

Finding alternative energy resources willbecome more important in years to come.

Oil

Prod

uctio

n

Year

Annual Oil Production—Past & Predicted

2050201019701930

Natural gas

Nitrogen oxidesCarbon dioxideParticulates

Petroleum Coal

Comparing Fossil Fuel Emissions

Most coal used inthe United States is burned to pro-duce steam to runelectric generators.

Petroleum supplies us withgasoline, kerosene, and waxas well as petrochemicals,which are used to makesynthetic fibers, such asrayon.

Natural gas is used in heating systems, in stoves andovens, and in vehicles asan alternative to gasoline.

Natural gas is the cleanestburning fossil fuel.

Coal

Petroleum

Natural Gas


Electrical Energy from Fossil Fuels One way to generateelectrical energy is to burn fossil fuels. In fact, fossil fuels arethe primary source of electrical energy generated in the UnitedStates. Earlier in this chapter, you learned that electrical energycan result from energy conversions. Kinetic energy is convertedinto electrical energy by an electric generator. This energyconversion is part of a larger process, shown in Figure 27, ofconverting the chemical energy in fossil fuels into the elec-trical energy you use every day.

Chapter 9234

1

2

3

4

5

6

Turn to page 243 to readabout a day in thelife of a power-plant manager.

Water is pumpedinto a boiler.

Coal, oil, or natural gas is burnedin a combustion chamber in orderto boil water. In this way, thechemical energy of the fossil fuelsis converted into thermal energy.

Thermal energy isused to boil waterand turn it to steam.

Thermal energy is con-verted into kinetic energyas the steam pushesagainst the blades of aturbine, causing the cen-tral shaft to spin.

An electric generator converts kineticenergy into electrical energy. Thecentral shaft from the turbine spins a large magnet within a ring of wirecoils. As the magnet spins, electriccurrent is generated in the wire coils.

The electrical energycan be distributed toa community throughelectrical wires.

Figure 27Converting Fossil Fuels into Electrical Energy

Nuclear Energy Another way to generate electrical energy isto use nuclear energy. Like fossil-fuel power plants, a nuclearpower plant generates thermal energy that boils water to pro-duce steam. The steam then turns a turbine, which rotates agenerator that converts kinetic energy into electrical energy.However, the fuels used in nuclear power plants are differentfrom fossil fuels. Nuclear energy is generated from radioactiveelements, such as uranium, shown in Figure 28. In a processcalled nuclear fission (FISH uhn), the nucleus of a uraniumatom is split into two smaller nuclei, releasing nuclear energy.Because the supply of these elements is limited, nuclear energycan be thought of as a nonrenewable resource.

Renewable ResourcesSome energy resources, called renewable resources, can be usedand replaced in nature over a relatively short period of time.Some renewable resources, such as solar energy and windenergy, are considered practically limitless.


Figure 28 A single uranium fuelpellet contains the energyequivalent of about 1 metric ton of coal.

Sunlight can be converted intoelectrical energy through solarcells, which can be used in devicessuch as calculators or installed in ahome to provide electrical energy.

Some houses allow sunlight into thehouse through large windows. Thesunlight is converted into thermalenergy that heats the house naturally.

Solar Energy

Energy from Water

The sun causes water to evaporate and fall again asrain that flows through rivers. The potential energy ofwater in a reservoir is converted into kinetic energy as the water flows downhill through a dam.

Falling water turns a turbine in a dam, which is connected to agenerator that converts kineticenergy into electrical energy.Electrical energy produced from falling water is called hydroelectricity.



Chapter 9236

Wind is caused by the sun’suneven heating of the Earth’ssurface, which creates currents of air. The kineticenergy of wind can turn the blades of a windmill.Windmills are often used to pump water from the ground.

Thermal energy resultingfrom the heating of Earth’s crust is calledgeothermal energy.Ground water that seeps into hot spots near the surface of the Earth can form geysers.

Wind Energy

Geothermal Energy

Some geothermal powerplants pump water under-ground into areas of hotrock. The water returns to the surface as steam,which can then be used to turn a generator to produce electrical energy.

Biomass

Certain plants can also beconverted into liquid fuel. For

example, corn can be used tomake ethanol, which is often

mixed with gasoline to make acleaner-burning fuel for cars.

Plants capture and store energy from thesun. Organic matter, such as plants, wood,and waste, that can be burned to releaseenergy is called biomass. Nonindustrializedcountries rely heavily on biomass for energy.

A wind turbine convertskinetic energy into electrical energy by rotating a generator.


The Two Sides to Energy ResourcesThe table below compares several energy resources. Dependingon where you live, what you need energy for, and how muchyou need, sometimes one energy resource is a better choicethan another.


1. Compare fossil fuels and biomass.

2. Why is nuclear energy a nonrenewable resource?

3. Trace electrical energy back to the sun.

4. Interpreting Graphics Use the pie chart at right to explainwhy renewable resources will become more important inyears to come.

REVIEW

Oil

Other

Nuclear

U.S. Energy Sources

Naturalgas

Coal

Fossil fuels provide a large amount of thermalenergy per unit of mass

easy to get and easy to transport

can be used to generate electrical energyand make products, such as plastic

Nuclear very concentrated form of energy

power plants do not produce smog

Solar almost limitless source of energy

does not produce pollution

Water renewable

does not produce air pollution

Wind renewable

relatively inexpensive to generate

does not produce air pollution

Geothermal almost limitless source of energy

power plants require little land

Biomass renewable

Energyresource Advantages Disadvantages

nonrenewable

burning produces smog

burning coal releases substances that can cause acid precipitation

risk of oil spills

produces radioactive waste

radioactive elements are nonrenewable

expensive to use for large-scale energyproduction

only practical in sunny areas

dams disrupt a river’s ecosystem

available only in areas that have rivers

only practical in windy areas

only practical in locations near hot spots

waste water can damage soil

requires large areas of farmland

produces smoke

Chapter Highlights

Chapter 9238

SECTION 1 SECTION 2

Vocabularyenergy (p. 214)

kinetic energy (p. 215)

potential energy (p. 216)

mechanical energy (p. 217)

Section Notes

• Energy is the ability to dowork, and work is the trans-fer of energy. Both energyand work are expressed in joules.

• Kinetic energy is energy ofmotion and depends onspeed and mass.

• Potential energy is energy of position or shape.Gravitational potentialenergy depends on weightand height.

• Mechanical energy is thesum of kinetic energy andpotential energy.

• Thermal energy, soundenergy, electrical energy, andlight energy can all be formsof kinetic energy.

• Chemical energy, electricalenergy, sound energy, andnuclear energy can all beforms of potential energy.

Vocabularyenergy conversion (p. 222)

Section Notes

• An energy conversion is achange from one form ofenergy to another. Any formof energy can be convertedinto any other form ofenergy.

• Machines can transfer energyand convert energy into amore useful form.

• Energy conversions help tomake energy useful bychanging energy into theform you need.

LabsFinding Energy (p. 668)

Energy of a Pendulum (p. 670)

Skills CheckVisual UnderstandingPOTENTIAL-KINETIC ENERGY CONVERSIONSWhen you jump up and down on a trampoline,potential and kinetic energy are converted backand forth. Review the picture of the pendulumon page 223 for another example of potential-kinetic energy conversions.

ENERGY RESOURCES Look back at the diagramon page 234. Converting fossil fuels into electri-cal energy requires several energy conversions.

Math ConceptsGRAVITATIONAL POTENTIAL ENERGY Tocalculate an object’s gravitational potentialenergy, multiply the weight of the object byits height above the Earth’s surface. For exam-ple, the gravitational potential energy (GPE) of a box that weighs 100 N and that is sittingin a moving truck 1.5 m above the ground iscalculated as follows:

GPE weight height

GPE 100 N 1.5 m 150 J


SECTION 3 SECTION 4

Vocabularyfriction (p. 229)

law of conservation of energy (p. 230)

Section Notes

• Because of friction, someenergy is always convertedinto thermal energy duringan energy conversion.

• Energy is conserved within aclosed system. According tothe law of conservation ofenergy, energy can be neithercreated nor destroyed.

• Perpetual motion is impossi-ble because some of the en-ergy put into a machine willbe converted into thermalenergy due to friction.

LabsEggstremely Fragile (p. 671)

Vocabularyenergy resource (p. 232)

nonrenewable resources (p. 232)

fossil fuels (p. 232)

renewable resources (p. 235)

Section Notes

• An energy resource is anatural resource that can beconverted into other formsof energy in order to douseful work.

• Nonrenewable resources can-not be replaced after they areused or can only be replacedafter long periods of time.They include fossil fuels andnuclear energy.

• Fossil fuels are nonrenewableresources formed from theremains of ancient organ-isms. Coal, petroleum, andnatural gas are fossil fuels.

• Renewable resources can beused and replaced in natureover a relatively short periodof time. They include solarenergy, wind energy, energyfrom water, geothermalenergy, and biomass.

•The sun is the source of mostenergy on Earth.

• Depending on where you liveand what you need energyfor, one energy resource canbe a better choice thananother.


TOPIC: What Is Energy? sciLINKS NUMBER: HSTP205

TOPIC: Forms of Energy sciLINKS NUMBER: HSTP210

TOPIC: Energy Conversions sciLINKS NUMBER: HSTP215

TOPIC: Law of Conservation of Energy sciLINKS NUMBER: HSTP217

TOPIC: Energy Resources sciLINKS NUMBER: HSTP225



KEYWORD: HSTENG

239Energy and Energy ResourcesCopyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter Review

Chapter 9240

USING VOCABULARY


1. potential energy/kinetic energy

2. friction/energy conversion

3. energy conversion/law of conservation of energy

4. energy resources/fossil fuels

5. renewable resources/nonrenewableresources


Multiple Choice

6. Kinetic energy depends ona. mass and volume.b. speed and weight.c. weight and height.d. speed and mass.

7. Gravitational potential energy depends ona. mass and speed.b. weight and height.c. mass and weight.d.height and distance.

8. Which of the following is not a renewableresource?a. wind energyb. nuclear energyc. solar energyd. geothermal energy

9. Which of the following is a conversionfrom chemical energy to thermal energy?a. Food is digested and used to regulate

body temperature.b. Charcoal is burned in a barbecue pit.c. Coal is burned to boil water.d.all of the above

10. Machines can a. increase energy.b. transfer energy.c. convert energy.d.Both (b) and (c)

11. In every energy conversion, some energy is always converted intoa. kinetic energy.b. potential energy.c. thermal energy.d.mechanical energy.

12. An object that has kinetic energy must bea. at rest.b. lifted above the Earth’s surface.c. in motion.d.None of the above

13. Which of the following is not a fossil fuel?a. gasoline c. firewoodb. coal d.natural gas

Short Answer

14. Name two forms of energy, and relatethem to kinetic or potential energy.

15. Give three specific examples of energyconversions.

16. Explain how energy is conserved within aclosed system.

17. How are fossil fuels formed?


Concept Mapping

18. Use the followingterms to create aconcept map: energy,machines, energyconversions, thermalenergy, friction.


19. What happens when you blow up a bal-loon and release it? Describe what youwould see in terms of energy.

20. After you coast down a hill on your bike,you eventually come to a complete stopunless you keep pedaling. Relate this tothe reason why perpetual motion isimpossible.

21. Look at the photo of the pole-vaulterbelow. Trace the energy conversionsinvolved in this event, beginning with the pole-vaulter’s breakfast of an orange-banana smoothie.

22. If the sun were exhausted of its nuclearenergy, what would happen to our energyresources on Earth?


10 m

5 m

500 Na

b

MATH IN SCIENCE

23. A box has 400 J of gravitational potentialenergy. a. How much work had to be done to give

the box that energy? b. If the box weighs 100 N, how far was it

lifted?


24. Look at the illustration below, and answerthe questions that follow.

a. What is the skier’s gravitationalpotential energy at point A?

b. What is the skier’s gravitational potentialenergy at point B?

c. What is the skier’s kinetic energy atpoint B? (Hint: mechanical energy potential energy kinetic energy.)



ReadingCheck-up


P H Y S I C A L S C I E N C E • L I F E S C I E N C E

Green Buildings

242

How do you make a building green withoutpainting it? You make sure it does as little dam-age to the environment as possible. Green, inthis case, does not refer to the color of pinetrees or grass. Instead, green means “environ-mentally safe.” And the “green movement” isgrowing quickly.

Green Methods and MaterialsOne strategy that architects employ to turn abuilding green is to minimize its energy con-sumption. They also reduce water use whereverpossible. One way to do this would be to cre-ate landscapes that use only native plants thatrequire little watering. Green builders also userecycled building materials whenever possible.For example, crushed light bulbs can be recy-cled into floor tiles, and recycled cotton canreplace fiberglass as insulation.

Seeing GreenAlthough green buildings cost more than con-ventional buildings to construct, they save a lotof money in the long run. For example, the

Audubon Building, in Manhattan, saves$100,000 in maintenance costs every year—thatis $60,000 in electricity bills alone! The buildinguses more than 60 percent less energy andelectricity than a conventional building does.Inside, the workers enjoy natural lighting,cleaner air, and an environment that is free ofunnecessary chemicals.

Some designers want to create buildingsthat are even more environmentally friendlythan the Audubon Building. Walls can be madeof straw bales or packed dirt, and landscapescan be maintained with rainwater collectedfrom rooftops. By conserving, recycling, andreducing waste, green builders are doing agreat deal to help the environment.

Design It Yourself! Design a building, a home, or even a dog-house that is made of only recycled materials.Be inventive! When you think you have the per-fect design, create a scale model. Describe howyour green structure saves resources.

The walls of this build-ing are being made out of worn-out tirespacked with soil. Thewalls will later becovered with stucco.


243

According to Cheryl Mele, her job as plant manager includes“anything that needs doing.” Her training as a mechanical

engineer allows her to conduct routine testing and to diagnoseproblems successfully. A firm believer in protecting our environ-ment, Mele operates the plant responsibly. Mele states, “It is veryimportant to keep the plant running properly and burning as effi-ciently as possible.” Her previous job helping to design more-efficient gas turbines helped make her a top candidate for the job of plant manager.

The Team ApproachMele uses the team approach to maintain the power plant. Shesays, “We think better as a team. We all have areas of expertiseand interest, and we maximize our effectiveness.” Mele observesthat working together makes everyone’s job easier.

Advice to Young PeopleMele believes that mechanical engineering and managing apower plant are interesting careers because you get to work withmany exciting new technologies. These professions are excellentchoices for both men and women. In these careers you interactwith creative people as you try to improve mechanical equipmentto make it more efficient and reduce harm to the environment.Her advice for young people is to pursue what interests you. “Besure to connect the math you learn to the science you are doing,”she says. “This will help you to understand both.”

As a power-plant manager,Cheryl Mele is responsible foralmost a billion watts of elec-tric power generation at theDecker Power Plant in Austin,Texas. More than 700 MW areproduced using a steam-driven turbine system withnatural gas fuel and oil as abackup fuel. Another 200 MWare generated by gas turbines.The steam-driven turbine sys-tem and gas turbines togetherprovide enough electricalenergy for many homes andbusinesses.

P O W E R - P L A N T M A N A G E R

A Challenge With the help of an adult,find out how much electricalenergy your home uses eachmonth. How many homes likeyours could Mele’s billion-wattpower plant supply energy toeach month?

Cheryl Mele managesthe Decker Power Plantin Austin, Texas.


244 Chapter 10

Heat and HeatTechnologyHeat and HeatTechnology

Up, Up, and AwayA hot-air balloon race is fun to watch. The balloons startout flat, but as they fill with hot air, the balloons growlarger until they are ready to take off. Balloons don't needengines or wings. They rely on heat and thermal expansionto get them off the ground and into the sky. In this chap-ter, you will learn more about heat and its place in yourdaily life.


1. How do you measure howhot or cold an object is?

2. What makes an object hotor cold?

3. How can heat be used inyour home?

Temperature . . . . . . . . 246QuickLab . . . . . . . . . . 247MathBreak . . . . . . . . . 249Internet Connect . . . . 250

What Is Heat? . . . . . . . 251QuickLab . . . . . . . . . . 253Apply . . . . . . . . . . . . . 254Internet Connect . . . . 255Meteorology

Connection . . . . . . . 256MathBreak . . . . . . . . . 257

Matter and Heat . . . . 260Biology Connection . . 262Internet Connect . . . . . 262

Heat Technology . . . . 263Oceanography

Connection . . . . . . . 266Environment

Connection . . . . . . . 269Internet Connect . . . . 269

Chapter Review . . . . . . . . . 272


LabBook . . . . . . . . . . . 672–675


Heat and Heat Technology 245

SOME LIKE IT HOTSometimes you can tell the relativetemperature of something by touch-ing it with your hand. In this activity,you will find out how well your handworks as a thermometer!

Procedure

1. Gather small pieces of the follow-ing materials from your teacher:metal, wood, plastic foam, rock,plastic, and cardboard.

2. Allow the materials to sit untouchedon a table for several minutes.

3. Put your hands palms down oneach of the various materials.Observe how warm or cool eachone feels.

4. In your ScienceLog, list the materi-als in order from coolest towarmest.

5. Place a thermometer strip on thesurface of each material. In yourScienceLog, record the temperatureof each material.

Analysis

6. Which material felt the warmest?

7. Which material had the highesttemperature? Was it the samematerial as in question 6?

8. Why do you think some materialsfelt warmer than others?

9. Was your hand a good ther-mometer? Why or why not?



Section

1

temperaturethermal expansionabsolute zero

Describe how temperaturerelates to kinetic energy.

Give examples of thermal expansion.

Compare temperatures ondifferent temperature scales.

Chapter 10246

TemperatureYou probably put on a sweater or a jacket when it’s cold out-side. Likewise, you probably wear shorts in the summer whenit gets hot. But how hot is hot, and how cold is cold? Thinkabout how the knobs on a water faucet are labeled “H” forhot and “C” for cold. But does only hot water come out whenthe hot water knob is on? You may have noticed that whenyou first turn on the water, it is warm or even cool. Are youbeing misled by the label on the knob? The terms hot and coldare not very scientific terms. If you really want to specify howhot or cold something is, you must use temperature.

What Is Temperature?You probably think of temperature as a measure of how hotor cold something is. But scientifically, temperature is a meas-ure of the average kinetic energy of the particles in an object.Using temperature instead of words like hot or cold reduces con-fusion. The scenario below emphasizes the importance of com-municating about temperature. You can learn more about hotand cold comparisons by doing the QuickLab on the next page.

Ready to go camping?

Almost!

There’s the ranger station.

Good! I’m getting cold. Thanks for the

hot cocoa.

Sure! I’m sorry—it feels warm up here to me, but I should have told you the

temperature.

Did you packshorts?

Yup. The ranger said it was warm

up there.


Temperature Depends on the Kinetic Energy of ParticlesAll matter is made of particles—atoms or molecules—that arein constant motion. Because the particles are in motion, theyhave kinetic energy. The faster the particles are moving, themore kinetic energy they have. What does temperature haveto do with kinetic energy? Well, as described in Figure 1, themore kinetic energy the particles of an object have, the higherthe temperature of the object.

Temperature Is an Average Measure Particles of matterare constantly moving, but they don’t all move at the samespeed and in the same direction all the time. Look back atFigure 1. As you can see, the motion of the particles is ran-dom. The particles of matter in an object move in differentdirections, and some particles move faster than others. Asa result, some particles have more kinetic energy than others.So what determines an object’s temperature? An object’s tem-perature is the best approximation of the kinetic energy ofthe particles. When you measure an object’s tempera-ture, you measure the average kinetic energy of theparticles in the object.

The temperature of a substance is not determinedby how much of the substance you have. As shownin Figure 2, different amounts of the same substancecan have the same temperature. However, the totalkinetic energy of the particles in each amount isdifferent. You will learn more about total kineticenergy in the next section.

247

Figure 1 The gasparticles on the righthave more kineticenergy than those onthe left. So, the gason the right is at ahigher temperature.

Figure 2 Even though there is more tea inthe teapot than in the mug, the temperatureof the tea in the mug is the same as the tem-perature of the tea in the teapot.

Heat and Heat Technology

Hot or Cold?

1. Put both your handsinto a bucket ofwarm water, andnote how it feels.

2. Now put one handinto a bucket of coldwater and the other into abucket of hot water.

3. After a minute, take yourhands out of the hot andcold water and put themback in the warm water.

4. Can you rely on yourhands to determinetemperature? In yourScienceLog, explain yourobservations.


Measuring TemperatureHow would you measure the temperature of a steaming cup ofhot chocolate? Would you take a sip of it or stick your fingerinto it? Probably not—you would use a thermometer.

Using a Thermometer Many thermometers are a thin glasstube filled with a liquid. Mercury and alcohol are often used inthermometers because they remain liquids over a large tem-perature range. Thermometers can measure temperature becauseof thermal expansion. Thermal expansion is the increase in vol-ume of a substance due to an increase in temperature. As a sub-stance gets hotter, its particles move faster. The particlesthemselves do not expand; they just spread out so that theentire substance expands. Different substances expand by dif-ferent amounts for a given temperature change. When youinsert a thermometer into a hot substance, the liquid inside thethermometer expands and rises. You measure the temperatureof a substance by measuring the expansion of the liquid in thethermometer.

Temperature Scales Temperature can be expressed accord-ing to different scales. Notice how the same temperatures havedifferent readings on the three temperature scales shown below.

Chapter 10248

The coldest temperature onrecord occurred in VostokStation, Antarctica. In 1983,the temperature dropped to–89°C (about –192°F). Thehottest temperature onrecord occurred in 1922 in aLibyan desert. A scorchingtemperature of 58°C (about136°F) was recorded—in theshade!

Three Temperature Scales

37˚ 310

212˚

98.6˚

32˚

100˚

20˚

0˚

373

293

273

68˚

Water boilsKelvinCelsiusFahrenheit

Body temperature

Room temperature

Water freezes


When you hear a weather report that gives the current tem-perature as 65°, chances are that you are given the tempera-ture in degrees Fahrenheit (°F). In science, the Celsius scale isused more often than the Fahrenheit scale. The Celsius scaleis divided into 100 equal parts, called degrees Celsius (°C),between the freezing point and boiling point of water. A thirdscale, called the Kelvin (or absolute) scale, is the official SI tem-perature scale. The Kelvin scale is divided into units calledkelvins (K)—not degrees kelvin. The lowest temperature on theKelvin scale is 0 K, which is called absolute zero. It is not pos-sible to reach a temperature lower than absolute zero. In fact,temperatures within a few billionths of a kelvin above absolutezero have been achieved in laboratories, but absolute zero itselfhas never been reached.

Temperature Conversion As shown by the thermometers illus-trated on the previous page, a given temperature is representedby different numbers on the three temperature scales. For exam-ple, the freezing point of water is 32°F, 0°C, or 273 K. As youcan see, 0°C is actually a much higher temperature than 0 K,but a change of 1 K is equal to a change of one Celsius degree.In addition, 0°C is a higher temperature than 0°F, but a changeof one Fahrenheit degree is not equal to a change of one Celsiusdegree. You can convert from one scale to another using thesimple equations shown below. After reading the examplesgiven, try the MathBreak on this page.

Heat and Heat Technology 249Copyright © by Holt, Rinehart and Winston. All rights reserved.

To convert

Celsius to Fahrenheit°C °F

Fahrenheit to Celsius°F °C

Celsius to Kelvin

°C K

Kelvin to CelsiusK °C

Use this equation:

°F 95 °C 32

°C 59 (°F 32)

K °C 273

°C K 273

Example

Convert 45°C to °F.

°F 95 45°C 32 113°F

Convert 68°F to °C.

°C 59 (68°F 32) 20°C

Convert 45°C to K.

K 45°C 273 318 K

Convert 32 K to °C.

°C 32 K 273 241°C

Converting TemperaturesUse the equations at left toanswer the following ques-tions:

1. What temperature on theCelsius scale is equivalentto 373 K?

2. Absolute zero is 0 K. Whatis the equivalent tempera-ture on the Celsius scale?on the Fahrenheit scale?

3. Which temperature iscolder, 0°F or 200 K?

MATH BREAK

What can you do at tempera-tures near absolute zero?

Turn to page 274 to find out!


More About Thermal ExpansionHave you ever gone across a highway bridge in a car? Youprobably heard and felt a “thuh-thunk” every couple of sec-onds as you went over the bridge. That sound occurs whenthe car goes over small gaps called expansion joints, shownin Figure 3. These joints keep the bridge from buckling as aresult of thermal expansion. Recall that thermal expansion isthe increase in volume of a substance due to an increase intemperature.

Thermal expansion also occurs in a thermostat, the devicethat controls the heater in your home. Inside a thermostat isa bimetallic strip. A bimetallic strip is made of two differentmetals stacked in a thin strip. Because different materials expandat different rates, one of the metals expands more than theother when the strip gets hot. This makes the strip coil anduncoil in response to changes in temperature. This coiling anduncoiling closes and opens an electric circuit that turns theheater on and off in your home, as shown in Figure 4.

Chapter 10250

Figure 3 The concrete segmentsof a bridge can expand on hotdays. When the temperaturedrops, the segments contract.

Figure 4 How a Thermostat Works

As the room tempera-ture drops below thedesired level, thebimetallic strip coils upand the glass tube tilts.A drop of mercurycloses an electric circuitthat turns the heater on.

As the room tempera-ture rises above thedesired level, thebimetallic strip uncoils.The drop of mercuryrolls back in the tube,opening the electric cir-cuit, and the heaterturns off.

Electrical contacts

a b

REVIEW

1. What is temperature?

2. What is the coldest temperature possible?

3. Convert 35°C to degrees Fahrenheit.

4. Inferring Conclusions Why do you think heating a fullpot of soup on the stove could cause the soup to overflow?

NSTA

TOPIC: What Is Temperature?GO TO: www.scilinks.orgsciLINKS NUMBER: HSTP230

251

What Is Heat?It’s time for your annual physical. The doctor comes in andbegins her exam by looking down your throat using a woodentongue depressor. Next she listens to your heart and lungs. Butwhen she places a metal stethoscope on your back, as shownin Figure 5, you jump a little and say, “Whoa! That’s cold!”The doctor apologizes and continues with your checkup.

Why did the metal stethoscope feel cold? After all, it wasat the same temperature as the tongue depressor, which didn’tmake you jump. What is it about the stethoscope that madeit feel cold? The answer has to do with how energy is trans-ferred between the metal and your skin. In this section, you’lllearn about this kind of energy transfer.

Heat Is a Transfer of Energy You might think of the word heat as having to do with thingsthat feel hot. But heat also has to do with things that feelcold—like the stethoscope. In fact, heat is what causes objectsto feel hot or cold or to get hot or cold under the right con-ditions. You probably use the word heat every day to meandifferent things. However, in this chapter, you will learn a spe-cific meaning for it. Heat is the transfer of energy betweenobjects that are at different temperatures.

Why do some things feel hot, while others feel cold? Whentwo objects at different temperatures come in

contact, energy is always transferred from theobject with the higher temperature to theobject with the lower temperature. Whenthe doctor’s stethoscope touches yourback, energy is transferred from your backto the stethoscope because your back hasa higher temperature (37°C) than thestethoscope (probably room temperature,20°C). So to you, the stethoscope is cold, but compared to the stethoscope,you are hot! You’ll learn why the tonguedepressor didn’t feel cold to you a littlelater in this section.

Figure 5 The reason the metal stethoscope feels cold is actually because of heat!


Section

2

heat insulatorthermal energy convectionconduction radiationconductor specific heat

capacity

Define heat as the transfer ofenergy between objects atdifferent temperatures.

Compare conduction,convection, and radiation.

Use specific heat capacity tocalculate heat.

Explain the differences betweentemperature, thermal energy,and heat.


Heat and Thermal Energy If heat is a transfer of energy,what form of energy is being transferred? The answer is ther-mal energy. Thermal energy is the total energy of the particlesthat make up a substance. Thermal energy, which is expressedin joules ( J), depends partly on temperature. An object at a

high temperature has more thermal energy than it would ata lower temperature. Thermal energy also depends on

how much of a substance you have. As described inFigure 6, the more moving particles there are in a sub-stance at a given temperature, the greater the thermalenergy of the substance.

When you hold an ice cube, thermal energy is trans-ferred from your hand to the ice cube. The ice cube’sthermal energy increases, and it starts to melt. But your

hand’s thermal energy decreases. The particles in the sur-face of your skin move more slowly, and the surface tempera-ture of your skin drops slightly. So your hand feels cold!

Reaching the Same Temperature Take a look at Figure 7.When objects at different temperatures come in contact, energywill always be transferred from the higher-temperature objectto the lower-temperature object until both objects reach thesame temperature. This point is called thermal equilibrium (EE kwi LIB ree uhm). When objects are at thermal equilibrium,no net change in either object’s thermal energy occurs. Althoughone object may have more thermal energy, both objects havethe same temperature.Figure 7

Reaching Thermal Equilibrium

1

3

Figure 6 Although both soupsare at the same temperature,the soup in the pan has morethermal energy than the soupin the bowl.

At thermal equilibrium, thejuice, bottle, and water havethe same temperature. Thejuice and bottle havebecome colder, and thewater has become warmer.

Energy is transferred from the particles in thejuice to the particles in the bottle. These parti-cles transfer energy to the particles in the icewater, causing the ice to melt. Water (9°C)

Bottle (9°C)Juice (9°C)

2 Thermal energy con-tinues to be transferredto the water after all ofthe ice has melted.

Juice (25°C)

Bottle (25°C)

Ice water (0°C)


Conduction, Convection, and RadiationSo far you’ve read about several examples of energy transfer:stoves transfer energy to substances in pots and pans; you canadjust the temperature of your bath water by adding cold orhot water to the tub; and the sun warms your skin. In the nextcouple of pages you’ll learn about three processes involving thistype of energy transfer: conduction, convection, and radiation.

Conduction Imagine that you put a cold metal spoon in abowl of hot soup, as shown in Figure 8. Soon the handle ofthe spoon warms up—even though it is not in the soup! Theentire spoon gets warm because of conduction. Conduction isthe transfer of thermal energy from one substance to anotherthrough direct contact. Conduction can also occur within asubstance, such as the spoon in Figure 8.

How does conduction work? As substances come in con-tact, particles collide and thermal energy is transferred fromthe higher-temperature substance to the lower-temperature sub-stance. Remember that particles of substances at different tem-peratures have different average kinetic energy. So whenparticles collide, higher-kinetic-energy particles transfer kineticenergy to lower-kinetic-energy particles. This makes some par-ticles slow down and other particles speed up until all parti-cles have the same average kinetic energy. As a result, thesubstances have the same temperature.

253

Figure 8 The end of this spoonwill warm up because conduction,the transfer of energy throughdirect contact, occurs all the wayup the handle.


Heat Exchange

1. Fill a film canisterwith hot water.Insert the ther-mometer apparatusprepared by your teacher.Record the temperature.

2. Fill a 250 mL beaker two-thirds full with cool water.Insert another thermom-eter in the cool water, andrecord its temperature.

3. Place the canister in the coolwater. Record the tempera-ture measured by each ther-mometer every 30 seconds.

4. When the thermometersread nearly the same tem-perature, stop and graphyour data. Plot temperature(y-axis) versus time (x-axis).

5. In your ScienceLog, describewhat happens to the rate ofenergy transfer as the twotemperatures get closer.



Keepin’ It Cool

The drink holder shown here ismade from a foamlike materialthat helps keep your can ofsoda cold. How is this drinkholder an insulator?

Conductors and Insulators Substances that conduct ther-mal energy very well are called conductors. For example, themetal in a doctor’s stethoscope is a conductor. Energy is trans-ferred rapidly from your higher-temperature skin to the room-temperature stethoscope. That’s why the stethoscope feels cold.Substances that do not conduct thermal energy very well arecalled insulators. For example, the doctor’s wooden tonguedepressor is an insulator. It has the same temperature as thestethoscope, but the tongue depressor doesn’t feel cold. That’sbecause thermal energy is transferred very slowly from yourtongue to the wood. Compare some typical conductors andinsulators in the chart at left.

Convection When you boil a pot of water, likethe one shown in Figure 9, the water moves inroughly circular patterns because of convection.Convection is the transfer of thermal energy bythe movement of a liquid or a gas. The waterat the bottom of a pot on a stove burner getshot because of contact with the pot itself (con-duction). As a result, the hot water becomes lessdense because its higher-energy particles havespread apart. The warmer water rises throughthe denser, cooler water above it. At the surface,the warm water begins to cool, and the lower-energy particles move closer together, makingthe water denser. The denser, cooler water sinksback to the bottom, where it will be heatedagain. This circular motion of liquids or gasesdue to density differences that result from tem-perature differences is called a convection current.

254

Figure 9 The repeated rising and sinking ofwater during boiling is due to convection.

Chapter 10

Curling iron

Iron skillet

Cookie sheet

Copper pipes

Stove coils

Flannel shirt

Oven mitt

Plastic spatula

Fiberglassinsulation

Ceramic bowl

Conductors Insulators


REVIEW

Radiation Unlike conduction and convection, radiation caninvolve either an energy transfer between particles of matteror an energy transfer across empty space. Radiation is thetransfer of energy through matter or space as electromagneticwaves, such as visible light and infrared waves.

All objects, including the heater in Figure 10, radiate elec-tromagnetic waves. The sun emits mostly visible light, whichyou can see and your body can absorb, making you feelwarmer. The Earth emits mostly infrared waves, which youcannot see but can still make you feel warmer.

Radiation and the Greenhouse Effect Earth’s atmosphere,like the windows of a greenhouse, allows the sun’s visible lightto pass through it. But like the windows of a greenhouse keepenergy inside the greenhouse, the atmosphere traps some rera-diated energy. This process, called the greenhouse effect, is illus-trated in Figure 11. Some scientists are concerned that highlevels of greenhouse gases (water vapor, carbon dioxide, andmethane) in the atmosphere may trap too much energy andmake Earth too warm. However, if not for the greenhouse effect,the Earth would be a cold, lifeless planet.

Figure 10 The coils of thisportable heater warm a roomby radiating visible light andinfrared waves.

Figure 11 The Greenhouse Effect

a

b c

Visible light passesthrough the atmosphereand heats the Earth.

The Earth radiates infraredwaves, some of whichescape into space.

Greenhouse gases trapsome of the reradiatedenergy near the Earth’ssurface.

1. What is heat?

2. Explain how radiation is different from conduction andconvection.

3. Applying Concepts Why do many metal cooking utensilshave wooden handles?

NSTA

TOPIC: What Is Heat?; Conduction, Convection, and Radiation




Heat and Temperature ChangeOn a hot summer day, have you ever fastened your seat beltin a car, as shown in Figure 12? If so, you may have noticedthat the metal buckle felt hotter than the cloth belt. Why?Keep reading to learn more.

Thermal Conductivity Different substances have different ther-mal conductivities. Thermal conductivity is the rate at which asubstance conducts thermal energy. Conductors, such as themetal buckle, have higher thermal conductivities than do insu-lators, such as the cloth belt. Because of the metal’s higher ther-mal conductivity, it transfers energy more rapidly to your handwhen you touch it than the cloth does. So even when the clothand metal are the same temperature, the metal feels hotter.

Specific Heat Capacity Another difference between the metaland the cloth is how easily they change temperature whenthey absorb or lose energy. When equal amounts of energyare transferred to or from equal masses of different substances,the change in temperature for each substance will differ. Specificheat capacity is the amount of energy needed to change thetemperature of 1 kg of a substance by 1°C.

Look at the table below. Notice that the specific heat capac-ity of the cloth of a seat belt is more than twice that of themetal seat belt buckle. This means that for equal masses ofmetal and cloth, less energy is required to change the tem-perature of the metal. So the metal buckle gets hot (and coolsoff) more quickly than an equal mass of the cloth belt.

Different substances have different specific heat capacities.Check out the specific heat capacities for various substancesin the table below.

Figure 12 On a hot summerday, the metal part of a seat beltfeels hotter than the cloth part.

Chapter 10256

Water has a higher specific heatcapacity than land. This differenceaffects the climate of different areason Earth. Climates in coastal areas aremoderated by the ocean. Because ofwater’s high specific heat capacity, theocean retains a lot of thermal energy.So even in the winter, when inlandtemperatures drop, coastal areas staymoderately warm. Because waterdoes not heat up as easily as landdoes, oceans can help to keep coastalareas cool during the summer wheninland temperatures soar.


Specific Heat Capacities of Some Common Substances

Specific heat Specific heatcapacity capacity

Substance (J/kg•°C) Substance (J/kg•°C)

Lead 128 Glass 837

Gold 129 Aluminum 899

Mercury 138 Cloth of seat belt 1,340

Silver 234 Wood 1,760

Copper 387 Steam 2,010

Iron 448 Ice 2,090

Metal of seat belt 500 Water 4,184


Heat—The Amount of Energy TransferredUnlike temperature, energy transferred be-tween objects cannot be measured directly—it must be calculated. When calculating energytransferred between objects, it is helpful todefine heat as the amount of energy that istransferred between two objects that are atdifferent temperatures. Heat can then beexpressed in joules (J).

How much energy is required to heat acup of water to make tea? To answer thisquestion, you have to consider the water’smass, its change in temperature, and its spe-cific heat capacity. In general, if you knowan object’s mass, its change in temperature,and its specific heat capacity, you can usethe equation below to calculate heat (theamount of energy transferred).

Heat ( J) specific heat capacity (J/kg•°C)

mass (kg) change in temperature (°C)

Calculating Heat Using the equation above and the data inFigure 13, you can follow the steps below to calculate the heatadded to the water. Because the water’s temperature increases,the value of heat is positive. You can also use this equationto calculate the heat removed from an object when it coolsdown. The value for heat would then be negative because thetemperature decreases.


Calculating Energy TransferUse the equation at left tosolve the following problems:

1. Imagine that you heat 2 Lof water to make pasta.The temperature of thewater before is 40°C, andthe temperature after is100°C. What is the heatinvolved? (Hint: 1 L ofwater = 1 kg of water)

2. Suppose you put a glassfilled with 180 mL of waterinto the refrigerator. Thetemperature of the waterbefore is 25°C, and thetemperature after is 10°C.How much energy wastransferred away from thewater as it became colder?

MATH BREAK

Write down what you know.Specific heat capacity of water = 4,184 J/kg•°CMass of water = 0.2 kgChange in temperature = 80°C – 25°C = 55°C

Substitute the values into the equation.Heat = specific heat capacity mass

change in temperature = 4,184 J/kg•°C 0.2 kg 55°C

Solve and cancel units.Heat = 4,184 J/kg•°C 0.2 kg 55°C

= 4,184 J 0.2 55 = 46,024 J

1

2

3

Figure 13 Information used to calculate heat,the amount of energy transferred to the water,is shown above.

Mass of water = 0.2 kgTemperature (before) = 25°CTemperature (after) = 80°C

Specific heat capacity of water = 4,184 J/kg•°C


Calorimeters When one object transfers thermal energy toanother object, the energy lost by one object is gained by theother object. This is the key to how a calorimeter (KAL uh RIMuh ter) works. Inside a calorimeter, shown in Figure 14, ther-mal energy is transferred from a known mass of a test sub-stance to a known mass of another substance, usually water.

Using a Calorimeter If a hot test substance is placed insidethe calorimeter’s inner container of water, the substance trans-fers energy to the water until thermal equilibrium is reached.By measuring the temperature change of the water and usingwater’s specific heat capacity, you can determine the exactamount of energy transferred by the test substance to the water.You can then use this amount of energy (heat), the change inthe test substance’s temperature, and the mass of the test sub-stance to calculate that substance’s specific heat capacity.

Calories and Kilocalories Heat can also be expressed inunits called calories. A calorie (cal) is the amount of energyneeded to change the temperature of 0.001 kg of water by 1°C.Therefore, 1,000 calories are required to change the temperatureof 1 kg of water by 1°C. One calorie is equivalent to 4.184 J.Another unit used to express heat is the kilocalorie (kcal), whichis equivalent to 1,000 calories. The kilocalorie is also knownas a Calorie (with a capital C). These are the Calories listed onfood labels, such as the label shown in Figure 15.

Figure 14 A calorimeter is usedto find the specific heat capacityof a substance.

Chapter 10258

Build your own calorimeter! Trythe lab on page 675 of the

LabBook.

Thermometer

Lid

Inner container

Insulated outercontainer

Test substance

Water

Stirrer

Figure 15 A serving of this fruitcontains 120 Cal (502,080 J) ofenergy that becomes availablewhen it is eaten and digested.


The Differences Between Temperature,Thermal Energy, and HeatSo far in this chapter, you have been learning about someconcepts that are closely related: temperature, heat, and ther-mal energy. But the differences between these concepts arevery important.

Temperature Versus Thermal Energy Temperature is a meas-ure of the average kinetic energy of an object’s particles, andthermal energy is the total energy of an object’s particles.While thermal energy varies with the mass of an object, tem-perature does not. A drop of boiling water has the same tem-perature as a pot of boiling water, but the pot has more thermalenergy because there are more particles.

Thermal Energy Versus Heat Heat and thermal energy arenot the same thing; heat is a transfer of thermal energy. Inaddition, heat can refer to the amount of energy transferredfrom one object to another. Objects contain thermal energy,but they do not contain heat. The table below summarizes thedifferences between temperature, thermal energy, and heat.


Self-CheckHow can two sub-stances have the sametemperature butdifferent amounts ofthermal energy? (Seepage 724 to check youranswer.)

Temperature Thermal energy Heat

A measure of the average The total energy of the The transfer of energy betweenkinetic energy of the particles particles in a substance objects that are at differentin a substance temperatures

Expressed in degrees Fahrenheit, Expressed in joules Amount of energy transferreddegrees Celsius, or kelvins expressed in joules or calories

Does not vary with the mass Varies with the mass and Varies with the mass, specific of a substance temperature of a substance heat capacity, and temperature

change of a substance

REVIEW

1. Some objects get hot more quickly than others. Why?

2. How are temperature and heat different?

3. Applying Concepts Examine the photo at right. How do you think the specific heat capacities for water and airinfluence the temperature of a swimming pool and thearea around it?

Chapter 10260

Matter and HeatHave you ever eaten a frozenjuice bar outside on a hotsummer day? It’s pretty hardto finish the entire thingbefore it starts to drip and makea big mess! The juice bar meltsbecause the sun radiates energy tothe air, which transfers energy to thefrozen juice bar. The energy absorbed bythe juice bar increases the kinetic energy of themolecules in the juice bar, which starts to turn to a liquid. Inthis section, you’ll learn more about how heat affects matter.

States of MatterThe matter that makes up a frozen juice bar has the same iden-tity whether the juice bar is frozen or has melted. The matteris just in a different form, or state. The states of matter are thephysical forms in which a substance can exist. Recall that mat-ter consists of particles—atoms or molecules—that can movearound at different speeds. The state a substance is in dependson the speed of its particles and the attraction between them.Three familiar states of matter are solid, liquid, and gas, repre-sented in Figure 16. You may recall that thermal energy is thetotal energy of the particles that make up a substance. Supposeyou have equal masses of a substance in its three states, each ata different temperature. The substance will have the most thermal energy as a gas and the least thermal energy as a solid.That’s because the particles move around fastest in a gas.


Particles of a gas move fastenough to overcome nearly all of the attraction betweenthem. The particles moveindependently of one another.


Particles of a solid do not movefast enough to overcome thestrong attraction between them,so they are held tightly together.The particles vibrate in place.

Section

3

states of matterchange of state

Identify three states of matter. Explain how heat affects matter

during a change of state. Describe how heat affects matter

during a chemical change.


Changes of StateWhen you melt cheese to make a cheese dip, like that shownin Figure 17, the cheese changes from a solid to a thick, gooeyliquid. A change of state is the conversion of a substance fromone physical form to another. A change of state is a physicalchange that affects one or more physical properties of a substancewithout changing the substance’s identity. Changes of stateinclude freezing (liquid to solid), melting (solid to liquid), boiling(liquid to gas), and condensing (gas to liquid).

Graphing Changes of State Suppose you put an ice cubein a pan and set the pan on a stove burner. Soon the ice willturn to water and then to steam. If you made a graph of theenergy involved versus the temperature of the ice during thisprocess, it would look something like the graph below.

As the ice is heated, its temperature increases from –25°Cto 0°C. At 0°C, the ice begins to melt. Notice that the tem-perature of the ice remains 0°C even as more energy is added.This added energy changes the arrangement of the particles,or molecules, in the ice. The temperature of the ice remainsconstant until all of the ice has become liquid water. At thatpoint, the water’s temperature will start to increase from 0°Cto 100°C. At 100°C, the water will begin to turn into steam.Even as more energy is added, the water’s temperature staysat 100°C. The energy added at the boiling point changes thearrangement of the particles until the water has entirelychanged to a gaseous state. When all of the water has becomesteam, the temperature again increases.

Figure 17 When you meltcheese, you change the state ofthe cheese but not its identity.


Self-CheckWhy do you think youcan get a more severeburn from steam thanfrom boiling water?(See page 724 to checkyour answer.)

–25

0

25

50

75

100

125

150

Changes of State for Water

Energy

Ice

Melting point

Boiling point

Ice + water

Water + steamSteam

Water

Tem

pera

ture

(°C

)


REVIEW

Heat and Chemical ChangesHeat is involved not only in changes of state, which are physi-cal changes, but also in chemical changes—changes that occurwhen one or more substances are changed into entirely newsubstances with different properties. During a chemical change,new substances are formed. For a new substance to form, oldbonds between particles must be broken and new bonds mustbe created. The breaking and creating of bonds between par-ticles involves energy. Sometimes a chemical change requiresthat thermal energy be absorbed. For example, photosynthesisis a chemical change in which carbon dioxide and water com-bine to form sugar and oxygen. In order for this change tooccur, energy must be absorbed. That energy is radiated by thesun. Other times, a chemical change, such as the one shownin Figure 18, will result in energy being released.

Chapter 10262

Figure 18 In a natural-gasfireplace, the methane in naturalgas and the oxygen in airchange into carbon dioxide andwater. As a result of the change,energy is given off, making aroom feel warmer.

1. During a change of state, why doesn’t the temperatureof the substance change?

2. Compare the thermal energy of 10 g of ice with thethermal energy of the same amount of water.

3. When water evaporates (changes from a liquid to agas), the air near the water’s surface becomes cooler.Explain why.

4. Applying Concepts Many cold packs used for sportsinjuries are activated by bending the package, causing thesubstances inside to interact. How is heat involved in thisprocess?


The substances your body needs tosurvive and grow come from food.Carbohydrates, proteins, and fats aremajor sources of energy for thebody. The energy content of foodcan be found by burning a dry foodsample in a special calorimeter. Bothcarbohydrates and proteins provide 4 Cal of energy per gram, while fatsprovide 9 Cal of energy per gram.

NSTA

TOPIC: Changes of StateGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP250



Figure 19A Hot-Water Heating System


Heat TechnologyYou probably wouldn’t be surprised to learn that the heater inyour home is an example of heat technology. But did you knowthat automobiles, refrigerators, and air conditioners are also exam-ples of heat technology? It’s true! You can travel long distances,you can keep your food cold, and you can feel comfortableindoors during the summer—all because of heat technology.

Heating SystemsMany homes and buildings have a central heating system thatcontrols the temperature in every room. On the next few pages,you will see some different central heating systems.

Hot-Water Heating The high specific heat capacity of watermakes it useful for heating systems. In a hot-water heating sys-tem, shown in Figure 19, water is heated by burning fuel (usu-ally natural gas or fuel oil) in a hot-water heater. The hot wateris pumped through pipes that lead to radiators in each room.The hot water heats the radiators, and the radiators then heatthe colder air surrounding them. The water returns to the hot-water heater to be heated again. A steam-heating system is simi-lar, except that steam is used in place of water.

Radiators

Smoke outlet

Hot-water heater

Pump

Air heated by the radiators circulates in the room by convection currents.

An expansion tank handles theincreased volume ofthe heated water.

Section

4

insulationheat enginethermal pollution

Analyze several kinds of heatingsystems.

Describe how a heat engineworks.

Explain how a refrigerator keepsfood cold.

Give examples of some effectsof heat technology on theenvironment.

Warm-Air Heating Although air has a lower specific heatcapacity than water, warm-air heating systems are used in manyhomes and offices in the United States. In a warm-air heatingsystem, shown in Figure 20, air is heated in a separate cham-ber by burning fuel (usually natural gas) in a furnace. The warmair travels through ducts to different rooms, which it entersthrough vents. The warm air heats air in the rooms. Cooler airsinks below the warm air and enters a vent near the floor. Thena fan forces the cooler air into the furnace, where the air willbe heated and returned to the ducts. An air filter cleans the airas it circulates through the system.

Heating and Insulation Thermal energy may be transferredout of a house during cold weather and into a house duringhot weather. To keep the house comfortable, a heating sys-tem must run almost continuously during the winter, and airconditioners often do the same during the summer. This canbe wasteful. That’s where insulation comes in. Insulation is a substance that reduces the transfer of thermal energy.Insulation, such as the fiberglass insulation shown in Figure 21,is made of insulators—materials that do not conduct thermalenergy very well. Insulation that is used in walls, ceilings,and floors helps a house stay warm in the winter and coolin the summer.

Do you remember the Earthships described at the beginningof this chapter? The tightly packed aluminum cans in the wallsof an Earthship have spaces between them. Air filling thesespaces insulates the Earthship. These homes also rely on a solarheating system, which you will learn about on the next page.

Figure 21 Millions of tiny airpockets in this insulation helpprevent thermal energy fromflowing into or out of a building.


Vent

DuctFurnace

Filter Fan

Smoke outlet

Figure 20A Warm-Air Heating System

Warm air is circulatedin the rooms byconvection currents.


Solar Heating The sun radiates an enormous amount of energy.Solar heating systems use this energy to heat houses and build-ings. Passive solar heating systems do not have moving parts.They rely on a building’s structural design and materials to useenergy from the sun as a means of heating. Active solar heatingsystems do have moving parts. They use pumps and fans to dis-tribute the sun’s energy throughout a building.

Look at the house in Figure 22. The large windows on thesouth side of the house are part of the passive solar heatingsystem. These windows receive maximum sunlight, and energyis radiated through the windows into the rooms. Thick, well-insulated concrete walls absorb energy and heat the house atnight or when it is cloudy. In the active solar heating system,water is pumped to the solar collector, where it is heated. Thehot water is pumped through pipes and transfers its energy tothem. A fan blowing over the pipes helps the pipes transfertheir thermal energy to the air. Warm air is then sent intorooms through vents. Cooler water returns to the water stor-age tank to be pumped back through the solar collector.


Waterstoragetank

Solar energycollector

Fan

Passive solar heating systemsutilize thick walls and largewindows that face south.

Active solar heating systemsoften consist of solar collec-tors, a network of pipes, afan, and a water storage tank.

Figure 22 Passive and activesolar heating systems worktogether to use the sun’s energyto heat an entire house.

Pumps


Heat EnginesDid you know that automobiles work because of heat? A car hasa heat engine, a machine that uses heat to do work. In a heatengine, fuel combines with oxygen in a chemical change thatproduces thermal energy. This process, called combustion, ishow engines burn fuel. Heat engines that burn fuel outside theengine are called external combustion engines. Heat engines thatburn fuel inside the engine are called internal combustion engines.In both types of engines, fuel is burned to produce thermalenergy that can be used to do work.

External Combustion Engine A simple steam engine, shownin Figure 23, is an example of an external combustion engine.Coal is burned to heat water in a boiler and change the waterto steam. When water changes to steam, it expands. The expand-ing steam is used to drive a piston, which can be attached toother mechanisms that do work, such as a flywheel. Modernsteam engines, such as those used to generate electrical energyat a power plant, drive turbines instead of pistons.

Chapter 10266

Figure 23 An External Combustion Engine

Steam enters throughthe open valve.

Used steam exitsthe cylinder throughan exhaust outlet.

Ocean engineers are developing anew technology known as OceanThermal Energy Conversion, or OTEC.OTEC uses temperature differencesbetween surface water and deepwater in the ocean to do work like a heat engine does. Warm surfacewater vaporizes a fluid, such asammonia, causing it to expand. Thencool water from ocean depths causesthe fluid to condense and contract.The continuous cycle of vaporizingand condensing converts thermalenergy into kinetic energy that canbe used to generate electrical energy.

OceanographyC O N N E C T I O N

a b As the piston moves to the other side, asecond valve opens and steam enters. Thesteam does work on the piston and movesit back. The motion of the piston turns aflywheel.

The expanding steam enters the cylinderfrom one side. The steam does work on thepiston, forcing the piston to move.

Cylinder Piston

Flywheel

Internal Combustion Engine In the six-cylinder car engineshown in Figure 24, fuel is burned inside the engine. Duringthe intake stroke, a mixture of gasoline and air enters each cylin-der as the piston moves down. Next the crankshaft turns andpushes the piston up, compressing the fuel mixture. This iscalled the compression stroke. Next comes the power stroke, inwhich the spark plug uses electrical energy to ignite the com-pressed fuel mixture, causing the mixture to expand and forcethe piston down. Finally, during the exhaust stroke, the crank-shaft turns and the piston is forced back up, pushing exhaustgases out of the cylinder.

Cooling SystemsWhen it gets hot in the summer, an air-conditioned room can feel very refreshing.Cooling systems are used to transfer thermalenergy out of a particular area so that it feelscooler. An air conditioner, shown in Figure 25,is a cooling system that transfers thermal energyfrom a warm area inside a building or car toan area outside, where it is often even warmer.But wait a minute—doesn’t that go against thenatural direction of heat—from higher tem-peratures to lower temperatures? Well, yes. Acooling system moves thermal energy fromcooler temperatures to warmer temperatures.But in order to do that, the cooling systemmust do work.

Figure 24 The continuouscycling of the four strokes in the cylinders converts thermalenergy into the kinetic energyrequired to make a car move.


Wire to spark plug

Cylinder

Crankshaft

Piston

Figure 25 This air conditioning unit keeps abuilding cool by moving thermal energy frominside the building to the outside.


Cooling Takes Energy Most cooling systems require electri-cal energy to do the work of cooling. The electrical energy isused by a device called a compressor. The compressor does thework of compressing the refrigerant, a gas that has a boilingpoint below room temperature. This property of the refriger-ant allows it to condense easily.

To keep many foods fresh, you store them in a refrigera-tor. A refrigerator is another example of a cooling system.Figure 26 shows how a refrigerator continuously transfers ther-mal energy from inside the refrigerator to the condenser coilson the outside of the refrigerator. That’s why the area near theback of a refrigerator feels warm.

Chapter 10268

Figure 26 How a Refrigerator Works

When the liquid passesthrough the expansion valve,it goes from a high-pressurearea to a low-pressure area.As a result, the temperatureof the liquid decreases.

The hot gas flows throughthe condenser coils onthe outside of the refrig-erator. The gas condensesinto a liquid, transferringsome of its thermalenergy to the coils.

The compressor uses electri-cal energy to compress therefrigerant gas; this compres-sion increases the pressureand temperature of the gas.

Low pressure

High pressure

The gas is thenreturned to thecompressor, andthe cycle repeats.

As the cold liquid refriger-ant moves through theevaporating coils, it absorbsthermal energy from therefrigerator compartment,making the inside of therefrigerator cold. As aresult, the temperature ofthe refrigerant increases,and it changes into a gas.

If you had a refrigerator inAntarctica, you would haveto heat it to keep it running.Otherwise, the refrigeratorwould transfer energy to its surroundings until itreached the same tempera-ture as its surroundings. Itwould freeze!

3

2

1

5

4

REVIEW

Heat Technology and Thermal PollutionHeating systems, car engines, and cooling systems all transferthermal energy to the environment. Unfortunately, too muchthermal energy can have a negative effect on the environment.

One of the negative effects of excess thermal energy isthermal pollution, the excessive heating of a body of water.Thermal pollution can occur near large power plants, whichare often located near a body of water. Electric power plantsburn fuel to produce thermal energy that is used to generateelectrical energy. Unfortunately, it is not possible for all of thatthermal energy to do work, so some waste thermal energyresults. Figure 27 shows how a cooling tower helps remove thiswaste thermal energy in order to keep the power plants oper-ating smoothly. In extreme cases, the increase in temperaturedownstream from a power plant can adversely affect the ecosys-tem of the river or lake. Some power plants reduce thermalpollution by reducing the temperature of the water before itis returned to the river.

Figure 27 Cool water is circulated through apower plant to absorb waste thermal energy.


Cool water Warm water

1. Compare a hot-water heating system with a warm-airheating system.

2. What is the difference between an external combustionengine and an internal combustion engine?

3. Analyzing Relationships How are changes of state animportant part of the way a refrigerator works?

Large cities can exhibit somethingcalled a heat island effect whenexcessive amounts of waste thermalenergy are added to the urban envi-ronment. This thermal energy comesfrom automobiles, factories, homeheating and cooling, lighting, andeven just the number of people liv-ing in a relatively small area. Theheat island effect can make the tem-perature of the air in a city higherthan that of the air in the surround-ing countryside.


NSTA

TOPIC: Heating SystemsGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP252

Skills Check

Chapter HighlightsSECTION 1 SECTION 2

Vocabularytemperature (p. 246)

thermal expansion (p. 248)

absolute zero (p. 249)

Section Notes

• Temperature is a measure ofthe average kinetic energy ofthe particles of a substance.It is a specific measurementof how hot or cold a sub-stance is.

• Thermal expansion is theincrease in volume of a sub-stance due to an increase intemperature. Temperature ismeasured according to theexpansion of the liquid in athermometer.

• Fahrenheit, Celsius, andKelvin are three temperaturescales.

• Absolute zero—0 K, or–273°C— is the lowest pos-sible temperature.

• A thermostat works accord-ing to the thermal expansionof a bimetallic strip.

Vocabularyheat (p. 251)

thermal energy (p. 252)

conduction (p. 253)

conductor (p. 254)

insulator (p. 254)

convection (p. 254)

radiation (p. 255)

specific heat capacity (p. 256)

Section Notes

• Heat is the transfer of energybetween objects that are atdifferent temperatures.

• Thermal energy is the totalenergy of the particles thatmake up a substance.

• Energy transfer will alwaysoccur from higher tempera-tures to lower temperaturesuntil thermal equilibrium isreached.

Math ConceptsTEMPERATURE CONVERSION To convertbetween different temperature scales, you canuse the equations found on page 249. Theexample below shows you how to convert aFahrenheit temperature to a Celsius temperature.


°C 59 (°F 32)

°C 59 (41°F 32)

°C 59 9 5°C

Visual UnderstandingHEAT—A TRANSFER OF ENERGYRemember that thermal energyis transferred between objectsat different temperatures untilboth objects reach the sametemperature. Look back atFigure 7, on page 252, toreview what you’ve learnedabout heat.



TOPIC: What Is Temperature? sciLINKS NUMBER: HSTP230

TOPIC: What Is Heat? sciLINKS NUMBER: HSTP240

TOPIC: Conduction, Convection, and Radiation sciLINKS NUMBER: HSTP245

TOPIC: Changes of State sciLINKS NUMBER: HSTP250

TOPIC: Heating Systems sciLINKS NUMBER: HSTP252



KEYWORD: HSTHOT

271Heat and Heat Technology

SECTION 3 SECTION 4SECTION 2

• Conduction, convection, andradiation are three methodsof energy transfer.

• Specific heat capacity is theamount of energy needed tochange the temperature of 1 kg of a substance by 1°C.Different substances have dif-ferent specific heat capacities.

• Energy transferred by heatcannot be measured directly.It must be calculated usingspecific heat capacity, mass,and change in temperature.

• A calorimeter is used todetermine the specific heatcapacity of a substance.

LabsFeel the Heat (p. 672)

Save the Cube! (p. 674)

Counting Calories (p. 675)

Vocabularystates of matter (p. 260)

change of state (p. 261)

Section Notes

• A substance’s state is deter-mined by the speed of its particles and the attractionbetween them.

• Thermal energy transferredduring a change of statedoes not change a sub-stance’s temperature. Rather,it causes a substance’s par-ticles to be rearranged.

• Chemical changes can causethermal energy to beabsorbed or released.

Vocabularyinsulation (p. 264)

heat engine (p. 266)

thermal pollution (p. 269)

Section Notes

• Central heating systemsinclude hot-water heatingsystems and warm-airheating systems.

• Solar heating systems can bepassive or active.

• Heat engines use heat to dowork. External combustionengines burn fuel outside theengine. Internal combustionengines burn fuel inside theengine.

• A cooling system transfersthermal energy from coolertemperatures to warmer tem-peratures by doing work.

• Transferring excess thermalenergy to lakes and rivers canresult in thermal pollution.


USING VOCABULARY


1. temperature/thermal energy

2. heat/thermal energy

3. conductor/insulator

4. conduction/convection

5. states of matter/change of state


Multiple Choice

6. Which of the following temperatures isthe lowest?a. 100°C c. 100 Kb. 100°F d.They are the same.

7. Compared with the Pacific Ocean, a cupof hot chocolate hasa. more thermal energy and a higher

temperature.b. less thermal energy and a higher

temperature.c. more thermal energy and a lower

temperature.d. less thermal energy and a lower

temperature.

8. The energy units on a food label area. degrees. c. calories.b. Calories. d. joules.

9. Which of the following materials wouldnot be a good insulator?a. wood c. metalb. cloth d. rubber

10. The engine in acar is a(n)a. heat engine.b. external combustion engine.c. internal combustion engine.d.Both (a) and (c)

11. Materials that warm up or cool down veryquickly have aa. low specific heat capacity.b. high specific heat capacity.c. low temperature.d.high temperature.

12. In an air conditioner, thermal energy isa. transferred from higher to lower

temperatures.b. transferred from lower to higher

temperatures.c. used to do work.d. taken from air outside a building and

transferred to air inside the building.

Short Answer

13. How does temperature relate to kineticenergy?

14. What is specific heat capacity?

15. Explain how heat affects matter during achange of state.

16. Describe how abimetallic stripworks in a thermostat.

Chapter 10272

Chapter Review


Concept Mapping

17. Use the followingterms to create a con-cept map: thermalenergy, temperature,radiation, heat, con-duction, convection.


18. Why does placing a jar under warmrunning water help loosen the lid onthe jar?

19. Why do you think a down-filled jacketkeeps you so warm? (Hint: Think aboutwhat insulation does.)

20. Would opening the refrigerator cool aroom in a house? Why or why not?

21. In a hot-air balloon, air is heated by aflame. Explain how this enables theballoon to float in the air.

MATH IN SCIENCE

22. The weather forecast calls for a tempera-ture of 86°F. What is the correspondingtemperature in degrees Celsius? inkelvins?

23. Suppose 1,300 mL of water are heatedfrom 20°C to 100°C. How much energywas transferred to the water? (Hint: Water’sspecific heat capacity is 4,184 J/kg•°C.)


Examine the graph below, and then answerthe questions that follow.

24. What physical change does this graphillustrate?

25. What is the freezing point of this liquid?

26. What is happening at the point where theline is horizontal?

–40

–30

–20

–10

0

10

20

30

Time

Freezing point

Liquid + solid

Solid

Liquid

Tem

pera

ture

(°C

)




ReadingCheck-up


274

Cryogenics—ColdTemperatureTechnologySupercold tempera-tures have led to some super-cool tech-nology. Cryosurgery,which is surgery thatuses extremely lowtemperatures, allowsdoctors to seal off tinyblood vessels during an operation or tofreeze diseased cellsand destroy them.

Cooling materials tonear absolute zero has

also led to the discovery of superconductors.Superconductors are materials that lose all oftheir electrical resistance when they are cooledto a low enough temperature. Imagine the possibilities for materials that could conductelectricity indefinitely without any energy loss.Unfortunately, it takes a great deal of energy tocool such materials. Right now, applications forsuperconductors are still just the stuff of dreams.

Freezing Fun on Your Own You can try your hand at cryoinvestigation.Place 50 mL of tap water, 50 mL of salt water(50 mL of water plus 15 g of salt), and 50 mLof rubbing alcohol (isopropanol) in three sepa-rate plastic containers. Then put all three con-tainers in your freezer at the same time. Checkthe containers every 5 minutes for 40 minutes.Which liquid freezes first? How can you explainany differences?

The Deep Freeze

In the dark reaches of outer space,temperatures can

drop below 270°C.Perhaps the only placecolder is a laboratoryhere on Earth!

The Quest for ZeroAll matter is made up oftiny, constantly vibratingparticles. Temperature isa measure of the aver-age kinetic energy ofthese particles. Thecolder a substance gets,the less kinetic energy its particles have and theslower the particles move. In theory, at absolutezero (273°C), all movement of matter shouldstop. Scientists are working in laboratories toslow down matter so much that the temperatureapproaches absolute zero.

How Low Can They Go?Using lasers, along with magnets, mirrors, andsupercold chemicals, scientists have cooled mat-ter to within a few billionths of a degree ofabsolute zero. In one method, scientists aimlasers at tiny gas particles inside a special cham-ber. The lasers hold the particles so still that theirtemperature approaches 272.999998°C.

To get an idea of what takes place, imagineturning on several garden hoses as high as theycan go. Then direct the streams of water at asoccer ball so that each stream pushes the ballfrom a different angle. If the hoses are aimedproperly, the ball won’t roll in any direction.That’s similar to what happens to the particles in the scientists’ experiment.

This laser device is used to coolmatter to nearly absolute zero.


275

E A R T H S C I E N C E • P H Y S I C A L S C I E N C E

DiAPLEX®: The Intelligent FabricWouldn’t it be great if you had a winter coat thatcould automatically adjust to keep you cozyregardless of the outside temperature? Well, sci-entists have developed a new fabric, calledDiAPLEX, that can be used to make such a coat!

With Pores or Without?Winter adventurers usually wear nylon fabrics tokeep warm. These nylon fabrics are laminatedwith a thin coating that contains thousands oftiny pores, or openings. The pores allow mois-ture, such as sweat from your body, and excessthermal energy to escape. You might think thepores would let moisture and cold air into thefabric, but that’s not the case. Because the poresare so small, the nylon fabric is windproof andwaterproof.

DiAPLEX is also made from laminated nylon,but the coating is different. DiAPLEX doesn’t havepores; it is a solid film. This film makes DiAPLEXeven more waterproof and breathable than otherlaminated nylon fabrics. So how does it work?

Moving ParticlesDiAPLEX keeps you warm by taking advantage ofhow particles move. When the air outside is cold,the particles of DiAPLEX arrange themselves into

a solid sheet, forming an insulator and preventingthe transfer of thermal energy from your body tocolder surroundings. As your body gets warm,such as after exercising, the fabric’s particlesrespond to your body’s increased thermal energy.Their kinetic energy increases, and they rearrangeto create millions of tiny openings that allowexcess thermal energy and moisture to escape.

Donning DiAPLEXDiAPLEX has a number of important advantagesover traditional nylon fabrics. Salts in perspirationand ice can clog the pores of traditional nylonfabrics, decreasing their ability to keep you warmand dry. But DiAPLEX does not have this problembecause it contains no pores. Because DiAPLEX isunaffected by UV light and is machine washable,it is also a durable fabric that is easy to care for.

Anatomy Connection Do some research to find out how your skinlets thermal energy and moisture escape.

When your body is cold, theDiAPLEX garment adjusts toprevent the transfer of thermalenergy from your body to itssurroundings, and you feel warmer.

When your body gets too warm, theDiAPLEX garment adjusts to allowyour body to transfer excess ther-mal energy and moisture to yoursurroundings, and you feel cooler.

Thermalenergy

Moisture


U N I T The Atom

Unit 4276

1911Ernest Rutherford, a physicist from

New Zealand, discovers the positively charged nucleus of the atom.

1932The neutron, one of the particles in the

nucleus of an atom, is discovered byBritish physicist James Chadwick.

1964Scientists propose the idea that smaller particlesmake up protons and neutrons. The particles arenamed quarks after a word used by James Joyce

in his book Finnegans Wake.

Around

400 B.C.The Greek philosopher Democritusproposes that small particles called

atoms make up all matter.

1945The United Nations is

formed. Its purpose is tomaintain world peace anddevelop friendly relations

between countries.

housands of yearsago, people began

asking the question,“What is matter madeof?” This unit followsthe discoveries andideas that have led toour current theoriesabout what makes upmatter. You will learnabout the atom—thebuilding block of allmatter—and its struc-ture. You will alsolearn how the periodictable is used to clas-sify and organize el-ements according topatterns in atomicstructure and otherproperties. This time-line illustrates some ofthe events that havebrought us to our cur-rent understanding ofatoms and of the peri-odic table in whichthey are organized.

T4

T I M E L I N E


The Atom 277

1848James Marshall finds gold

while building Sutter’sMill, starting the California

gold rush.

1803British scientist and school

teacher John Dalton reintroduces the concept of

atoms with evidence tosupport his ideas.

1869Russian chemist

Dmitri Mendeleevdevelops a periodictable that organizesthe elements known

at the time.

1898

British scientists Sir William Ramsay and

Morris W. Travers discoverthree elements—krypton,

neon, and xenon—in threemonths. The periodic tabledeveloped by Mendeleev

helps guide their research.

1996Another element is added to the periodic tableafter a team of German scientists synthesize an

atom containing 112 protons in its nucleus.

1989Germans celebrate when the BerlinWall ceases to function as a barrierbetween East and West Germany.

1897British scientist J. J.

Thomson identifies elec-trons as particles that are

present in every atom.

1981Scientists in Switzerland develop a

scanning tunneling microscope,which is used to see atoms for the

first time.


278 Chapter 11

Development of the Atomic Theory . . . . . . 280

InternetConnect . . . . . . 283, 286

The Atom . . . . . . . . . . 287Astronomy

Connection . . . . . . . 290Apply . . . . . . . . . . . . . 291MathBreak . . . . . . . . . 292Internet Connect . . . . 293

Chapter Review . . . . . . . . . 296


LabBook . . . . . . . . . . . 676–677

Introductionto AtomsIntroductionto Atoms

Atomic BubblesYou probably have made bubbles with a plastic wand and a soapy liquid. To trace the paths of atoms, some scientistsalso made bubbles, but they did not use a wand. They useda bubble chamber. A bubble chamber is filled with a hot,pressurized liquid that forms bubbles when a charged particle moves through it. Why are scientists interested inbubbles? The bubbles give them information about particlescalled atoms that make up all objects. In this chapter, youwill learn about atoms and experiments that led to themodern atomic theory. You will also learn about the partsand structure of an atom.


1. What are some ways thatscientists have describedthe atom?

2. What are the parts of theatom, and how are theyarranged?

3. How are atoms of all elements alike?


279

WHERE IS IT?Some theories about the internalstructure of atoms were formed byobserving the effects of aiming verysmall moving particles at atoms. Inthis activity, you will form an ideaabout the location and size of a hid-den object by rolling marbles at it.

Procedure

1. Place a rectangular piece of card-board on four books or blocks sothat each corner of the cardboardrests on a book or block.

2. Ask your teacher to place theunknown object under the card-board. Be sure that you do not see the object.

3. Place a large piece of paper on top of the cardboard.

4. Carefully roll a marble under thecardboard. Record on the paperthe position where the marbleenters and exits. Also record thedirection it travels.

5. Keep rolling the marble from dif-ferent directions to collect dataabout the shape and location ofthe object.

6. Write down all your observations in your ScienceLog.

Analysis

7. Form a conclusion about theobject’s shape, size, and location.Record your conclusion in yourScienceLog.

Introduction to AtomsCopyright © by Holt, Rinehart and Winston. All rights reserved.


Chapter 11280

Development of the Atomic TheoryThe photo at right showsuranium atoms magnified 3.5 million times by a scan-ning tunneling microscope.An atom is the smallestparticle into which an el-ement can be divided andstill be the same substance.Atoms make up elements;elements combine to formcompounds. Because allmatter is made of elementsor compounds, atoms areoften called the buildingblocks of matter.

Before the scanning tunneling microscope was invented,in 1981, no one had ever seen an atom. But the existence ofatoms is not a new idea. In fact, atomic theory has beenaround for more than 2,000 years. A theory is a unifying expla-nation for a broad range of hypotheses and observations thathave been supported by testing. In this section, you will travelthrough history to see how our understanding of atoms hasdeveloped. Your first stop—ancient Greece.

Democritus Proposes the AtomImagine that you cut the silver coin shown in Figure 1 inhalf, then cut those halves in half, and so on. Could youkeep cutting the pieces in half forever? Around 440 B.C., a Greek philosopher named Democritus (di MAHK ruh tuhs)proposed that you would eventually end up with an “uncut-

table” particle. He called this particle an atom (from theGreek word atomos, meaning “indivisible”). Democritus

proposed that all atoms are small, hard particles madeof a single material formed into different shapes andsizes. He also claimed that atoms are always moving and that they form different materials byjoining together.

Figure 1 This coin was in use during Democritus’stime. Democritus thought the smallest particle in anobject like this silver coin was an atom.

Section

1

atom modeltheory nucleuselectrons electron clouds

Describe some of the experi-ments that led to the currentatomic theory.

Compare the different modelsof the atom.

Explain how the atomic theoryhas changed as scientists havediscovered new informationabout the atom.


Aristotle Disagrees Aristotle (ER is TAHT uhl), a Greek philoso-pher who lived from 384 to 322 B.C., disagreed withDemocritus’s ideas. He believed that you would never end upwith an indivisible particle. Although Aristotle’s ideas wereeventually proved incorrect, he had such a strong influenceon popular belief that Democritus’s ideas were largely ignoredfor centuries.

Dalton Creates an Atomic Theory Based on ExperimentsBy the late 1700s, scientists had learned that elements combine in specific proportions based on mass to form compounds. For example, hydrogen and oxygen always combine in the same proportion to form water. John Dalton,a British chemist and school teacher, wanted to know why.He performed experiments with different substances. Hisresults demonstrated that elements combine in specific proportions because they are made of individual atoms.Dalton, shown in Figure 2, published his own atomic theoryin 1803. His theory stated the following:

Not Quite Correct Toward the end of the nineteenthcentury scientists agreed that Dalton’s theory explainedmany of their observations. However, as new infor-mation was discovered that could not be explainedby Dalton’s ideas, the atomic theory was revisedto more correctly describe the atom. As youread on, you will learn how Dalton’s theoryhas changed, step by step, into the currentatomic theory.

Introduction to Atoms 281

All substances are made of atoms.Atoms are small particles that cannotbe created, divided, or destroyed.

Atoms of the same element are exactly alike, and atoms of different elements are different.

Atoms join with other atoms tomake new substances.

In 342 or 343 B.C., KingPhillip II of Macedonappointed Aristotle to be atutor for his son, Alexander.Alexander later conqueredGreece and the PersianEmpire (in what is now Iran)and became known asAlexander the Great.

Figure 2 John Dalton developed his atomic

theory from observationsgathered from manyexperiments.


Thomson Finds Electrons in the AtomIn 1897, a British scientist named J. J. Thomson made a dis-covery that identified an error in Dalton’s theory. Using sim-ple equipment (compared with modern equipment), Thomsondiscovered that there are small particles inside the atom.Therefore, atoms can be divided into even smaller parts.

Thomson experimented with a cathode-ray tube, as shownin Figure 3. He discovered that a positively charged plate(marked with a positive sign in the illustration) attracts the beam. Thomson concluded that the beam was made ofparticles with a negative electric charge.

Just What Is Electric Charge?

Have you ever rubbed a balloon on your hair? The propertiesof your hair and the balloon seem to change, making them

attract one another. To describe these observations, scientistssay that the balloon and your hair become “charged.” There are

two types of electric charges—positive and negative. Objects withopposite charges attract each other, while objects with the same

charge push each other away.

Figure 3 Thomson’s Cathode-Ray Tube Experiment

Chapter 11282

When the plates were charged, thebeam produced a glowing spothere after being pulled toward thepositively charged plate.

Metal plates could be charged to changethe path of the beam.

When the plates were not charged, thebeam produced a glowing spot here.

Almost all gas was removedfrom the glass tube.

An invisible beam was produced when the tube was connected toa source of electrical energy.

–

+

e

a

b

c

d


Negative Corpuscles Thomson repeated his experiment sev-eral times and found that the particle beam behaved in exactlythe same way each time. He called the particles in the beamcorpuscles (KOR PUHS uhls). His results led him to concludethat corpuscles are present in every type of atom and that allcorpuscles are identical. The negatively charged particles foundin all atoms are now called electrons.

Like Plums in a Pudding Thomson revised the atomic theory to account for the presence of electrons. BecauseThomson knew that atoms have no overall charge, he realizedthat positive charges must be present to balance the negativecharges of the electrons. But Thomson didn’t know the loca-tion of the electrons or of the positive charges. So he proposeda model to describe a possible structure of the atom. A modelis a representation of an object or system. A model is differ-ent from a theory in that a model presents a picture of whatthe theory explains.

Thomson’s model, illustrated in Figure 4, came to beknown as the plum-pudding model, named for anEnglish dessert that was popular at the time.Today you might call Thomson’s modelthe chocolate-chip-ice-cream model; elec-trons in the atom could be compared tothe chocolate chips found throughoutthe ice cream!

Introduction to Atoms 283Introduction to Atoms

1. What discovery demonstrated that atoms are not thesmallest particles?

2. What did Dalton do in developing his theory thatDemocritus did not do?

3. Analyzing Methods Why was it important for Thomsonto repeat his experiment?

The word electron comesfrom a Greek word meaning“amber.” A piece of amber(the solidified sap fromancient trees) attracts smallbits of paper after beingrubbed with cloth.

REVIEW

The atom is mostlypositively chargedmaterial.

Electrons aresmall, negativelycharged particleslocated through-out the positivematerial.

Figure 4 Thomson’s plum-pudding model of the atom is shown above. A modern version ofThomson’s model might be chocolate-chip ice cream.

NSTA

TOPIC: Development of the Atomic Theory



"It was quite the most incredible event that has ever happened

to me in my life. It was almost as if you fired a fifteen-inch shell

into a piece of tissue paper and it came back and hit you."

Figure 5 Rutherford’s Gold Foil Experiment

Chapter 11284

An element such as radium producedthe particles.

Some particleswere slightlydeflected froma straight path.

a

d

Rutherford Opens an Atomic “Shooting Gallery”In 1909, a former student of Thomson’s named ErnestRutherford decided to test Thomson’s theory. He designed anexperiment to investigate the structure of the atom. He aimeda beam of small, positively charged particles at a thin sheetof gold foil. These particles were larger than protons, evensmaller positive particles identified in 1902. Figure 5 shows adiagram of Rutherford’s experiment. To find out where theparticles went after being “shot” at the gold foil, Rutherfordsurrounded the foil with a screen coated with zinc sulfide, asubstance that glowed when struck by the particles.

Rutherford Gets Surprising Results Rutherford thoughtthat if atoms were soft “blobs” of material, as suggested byThomson, then the particles would pass through the gold andcontinue in a straight line. Most of the particles did just that.But to Rutherford’s great surprise, some of the particles weredeflected (turned to one side) a little, some were deflected a great deal, and some particles seemed to bounce back.Rutherford reportedly said,

Find out aboutMelissa

Franklin, amodern atomexplorer, onpage 299.

Most of theparticles passedstraight throughthe gold foil.

c

Lead stopped all of the positiveparticles except for a small streamaimed at a gold foil target.

b

Very few particlesseemed to bounce back.

e


Rutherford Presents a New Atomic Model Rutherford real-ized that the plum-pudding model of the atom did not explainhis results. In 1911, he revised the atomic theory and de-veloped a new model of the atom, as shown in Figure 6. Toexplain the deflection of the particles, Rutherford proposedthat in the center of the atom is a tiny, extremely dense, positively charged region called the nucleus (NOO klee uhs).Most of the atom’s mass is concentrated here. Rutherford reasoned that positively charged particles that passed close bythe nucleus were pushed away by the positive charges in the nucleus. A particle that headedstraight for a nucleus would bepushed almost straight back inthe direction from which itcame. From his results,Rutherford calculated thatthe diameter of the nu-cleus was 100,000 timessmaller than the diam-eter of the gold atom. Toimagine how small this is,look at Figure 7.


Figure 7 The diameter of this pinhead is 100,000 times smallerthan the diameter of the stadium.

Self-CheckWhy did Thomson think the atom contains positivecharges? (See page 724 to check your answer.)

Figure 6Rutherford’s Model of the Atom

The atom has a small, dense,positively charged nucleus.

The atom is mostly empty space throughwhich electrons travel.

Electrons travel around thenucleus like planets aroundthe sun, but their exactarrangement could not be described.


Bohr States That Electrons Can Jump Between LevelsIn 1913, Niels Bohr, a Danish scientist who workedwith Rutherford, suggested that electrons travelaround the nucleus in definite paths. These pathsare located in levels at certain distances from thenucleus, as illustrated in Figure 8. Bohr proposedthat no paths are located between the levels, butelectrons can jump from a path in one level to apath in another level. Think of the levels as rungson a ladder. You can stand on the rungs of a lad-der but not between the rungs. Bohr’s model was a valuable tool in predicting some atomic behav-ior, but the atomic theory still had room forimprovement.

The Modern Theory: ElectronClouds Surround the NucleusMany twentieth-century scientists have con-tributed to our current understanding of the atom.An Austrian physicist named Erwin Schrödingerand a German physicist named Werner Heisenbergmade particularly important contributions. Theirwork further explained the nature of electrons inthe atom. For example, electrons do not travel indefinite paths as Bohr suggested. In fact, the exactpath of a moving electron cannot be predicted.According to the current theory, there are regionsinside the atom where electrons are likely to befound—these regions are called electron clouds.Electron clouds are related to the paths describedin Bohr’s model. The electron-cloud model of theatom is illustrated in Figure 9.

286

Electron paths

Figure 8 Bohr’s Model of the Atom

1. In what part of an atom is most of its mass located?

2. What are two differences between the atomic theorydescribed by Thomson and that described by Rutherford?

3. Comparing Concepts Identify the difference in howBohr’s theory and the modern theory describe the loca-tion of electrons.

Chapter 11

Nucleus

Electron cloudsNucleus

REVIEW

Figure 9 The Current Model of the Atom

NSTA

TOPIC: Modern Atomic TheoryGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP260



The AtomIn the last section, you learned how the atomic theory de-veloped through centuries of observation and experimenta-tion. Now it’s time to learn about the atom itself. In thissection, you’ll learn about the particles inside the atom, andyou’ll learn about the forces that act on those particles. Butfirst you’ll find out just how small an atom really is.

How Small Is an Atom?The photograph below shows the pattern that forms when abeam of electrons is directed at a sample of aluminum. By ana-lyzing this pattern, scientists can determine the size of an atom.Analysis of similar patterns for many elements has shown thataluminum atoms, whichare average-sized atoms,have a diameter of about0.00000003 cm. That’s threehundred-millionths of acentimeter. That is so smallthat it would take a stack of 50,000 aluminum atomsto equal the thickness of a sheet of aluminum foilfrom your kitchen!

As another example, consider an ordinary penny.Believe it or not, a pennycontains about 2 1022 atoms, which can be written as 20,000,000,000,000,000,000,000 atoms, of copper and zinc. That’s twenty thousand billion billion atoms—over3,000,000,000,000 times more atoms than there are people on Earth! So if there are that many atoms in a penny, eachatom must be very small. You can get a better idea of just howsmall an atom is in Figure 10.

Figure 10 If you could enlarge a penny untilit was as wide as the continental United

States, each of its atoms would beonly about 3 cm in diameter—aboutthe size of this table-tennis ball.

The size of atoms varieswidely. Helium atoms havethe smallest diameter, andfrancium atoms have thelargest diameter. In fact,about 600 atoms of heliumwould fit in the space occu-pied by a single franciumatom!

Section

2

protonsatomic mass unitneutronsatomic numberisotopesmass numberatomic mass

Compare the charge, location,and relative mass of protons,neutrons, and electrons.

Calculate the number of parti-cles in an atom using the atomicnumber, mass number, andoverall charge.

Calculate the atomic mass ofelements.


What’s Inside an Atom?As tiny as an atom is, it consists of even smaller particles—protons, neutrons, and electrons—as shown in the model inFigure 11. (The particles represented in the figures are not shownin their correct proportions because the electrons would betoo small to see.)

The Nucleus Protons are the positively charged particles ofthe nucleus. It was these particles that repelled Rutherford’s“bullets.” All protons are identical. The mass of a proton isapproximately 1.7 1024 g, which can also be written as0.0000000000000000000000017 g. Because the masses of particles in atoms are so small, scientists developed a newunit for them. The SI unit used to express the masses ofparticles in atoms is the atomic mass unit (amu). Scientistsassign each proton a mass of 1 amu.

Neutrons are the particles of the nucleus that have nocharge. All neutrons are identical. Neutrons are slightly moremassive than protons, but the difference in mass is so smallthat neutrons are also given a mass of 1 amu.

Protons and neutrons are the most massive particles inan atom, yet the nucleus has a very small volume. So thenucleus is very dense. If it were possible to have a nucleusthe volume of an average grape, that nucleus would have amass greater than 9 million metric tons!

Chapter 11288

Proton Profile

Charge: positive

Mass: 1 amu

Location: nucleus

Neutron Profile

Charge: none

Mass: 1 amu

Location: nucleus

Protons are positivelycharged particles in thenucleus of an atom.

Neutrons are particles inthe nucleus of an atomthat have no charge.

Figure 11 Parts of an Atom

Electrons are negatively charged particlesfound in electron clouds outside thenucleus. The size of the electron cloudsdetermines the size of the atom.

The nucleus is the small,dense, positively chargedcenter of the atom. Itcontains most of theatom’s mass.

The diameter of thenucleus is 1/100,000 the diameter of the atom.


Outside of the Nucleus Electrons are the negatively chargedparticles in atoms. Electrons are likely to be found around thenucleus within electron clouds. The charges of protons andelectrons are opposite but equal in size. An atom is neutral(has no overall charge) because there are equal numbers ofprotons and electrons, so their charges cancel out. If the num-bers of electrons and protons are not equal, the atom becomesa charged particle called an ion (IE ahn). Ions are positivelycharged if the protons outnumber the electrons, and they arenegatively charged if the electrons outnumber the protons.

Electrons are very small in mass compared with protonsand neutrons. It takes more than 1,800 electrons to equal themass of 1 proton. In fact, the mass of an electron is so smallthat it is usually considered to be zero.

How Do Atoms of Different Elements Differ?There are over 110 different elements, each of which ismade of different atoms. What makes atoms different fromeach other? To find out, imagine that it’s possible to “build”an atom by putting together protons, neutrons, and electrons.

Starting Simply It’s easiest to start with the simplestatom. Protons and electrons are found in all atoms, andthe simplest atom consists of just one of each. It’s so simple it doesn’t even have a neutron. Put just one proton in the center of the atom for thenucleus. Then put one electron in the electron cloud, as shown in the model inFigure 12. Congratulations! You have justmade the simplest atom—a hydrogen atom.

1. What particles form the nucleus?

2.Explain why atoms are neutral.

3. Summarizing Data Why do scientists say that most ofthe mass of an atom is located in the nucleus?

REVIEW

Electron Profile

Charge: negative

Mass: almost zero

Location: electron clouds

Electron

Figure 12 The simplest atomhas one proton and one electron.


Help wanted! Elements-4-Uneeds qualified nucleus

builders. Report to page 676 of the LabBook.

Proton


Now for Some Neutrons Now build an atom containingtwo protons. Both of the protons are positively charged, sothey repel one another. You cannot form a nucleus with themunless you add some neutrons. For this atom, two neutronswill do. Your new atom will also need two electrons outsidethe nucleus, as shown in the model in Figure 13. This is anatom of the element helium.

Building Bigger Atoms You could build a carbon atom using6 protons, 6 neutrons, and 6 electrons; or you could build anoxygen atom using 8 protons, 9 neutrons, and 8 electrons.You could even build a gold atom with 79 protons, 118 neu-trons, and 79 electrons! As you can see, an atom does not haveto have equal numbers of protons and neutrons.

The Number of Protons Determines the Element Howcan you tell which elements these atoms represent? The keyis the number of protons. The number of protons in the nucleusof an atom is the atomic number of that atom. All atoms ofan element have the same atomic number. Every hydrogenatom has only one proton in its nucleus, so hydrogen has anatomic number of 1. Every carbon atom has six protons in itsnucleus, so carbon has an atomic number of 6.

Are All Atoms of an Element the Same?Back in the atom-building workshop, you make an atom thathas one proton, one electron, and one neutron, as shown inFigure 14. The atomic number of this new atom is 1, so theatom is hydrogen. However, this hydrogen atom’s nucleus hastwo particles; therefore, this atom has a greater mass than thefirst hydrogen atom you made. What you have is another iso-tope (IE suh TOHP) of hydrogen. Isotopes are atoms that havethe same number of protonsbut have different numbers ofneutrons. Atoms that are iso-topes of each other are alwaysthe same element because thenumber of protons in eachatom is the same.

Chapter 11290

ProtonElectron

Neutron

Figure 13 A helium nucleusmust have neutrons in it to keepthe protons from moving apart.

Neutron

ElectronProton

Figure 14 The atom in this modeland the one in Figure 12 are isotopesbecause each has one proton but adifferent number of neutrons.


Hydrogen is the most abundant el-ement in the universe. It is the fuelfor the sun and other stars. It is cur-rently believed that there are roughly2,000 times more hydrogen atomsthan oxygen atoms and 10,000times more hydrogen atoms thancarbon atoms.


Properties of Isotopes Each el-ement has a limited number of iso-topes that occur naturally. Someisotopes of an element have uniqueproperties because they are unsta-ble. An unstable atom is an atomwhose nucleus can change its com-position. This type of isotope isradioactive. However, isotopes of anelement share most of the samechemical and physical properties.For example, the most commonoxygen isotope has 8 neutrons inthe nucleus, but other isotopes have9 or 10 neutrons. All three isotopesare colorless, odorless gases at room temperature.Each isotope has the chemical property of combin-ing with a substance as it burns and even behavesthe same in chemical changes in your body.

How Can You Tell One Isotope from Another?You can identify each isotope of an element by itsmass number. The mass number is the sum of the pro-tons and neutrons in an atom. Electrons are notincluded in an atom’s mass number because theirmass is so small that they have very little effect onthe atom’s total mass. Look at the boron isotope models shown in Figure 15 to see how to calculatean atom’s mass number.


Figure 15 Each of these boron isotopes has five protons.But because each has a different number of neutrons,each has a different mass number.

Protons: 5Neutrons: 5Electrons: 5Mass number = protons + neutrons = 10

Protons: 5Neutrons: 6Electrons: 5Mass number = protons + neutrons = 11

Isotopes and Light BulbsOxygen reacts, or undergoes a chemical change, with the hot filament in a light bulb, quickly burning out thebulb. Argon does not react with the filament, so a light bulb filled with argon burns out more slowly than one filled with oxygen. Do all three naturally-occurring isotopes of argon have thesame effect in light bulbs?Explain your reasoning.

Naming Isotopes To identify a specific isotope of an el-ement, write the name of the element followed by a hyphenand the mass number of the isotope. A hydrogen atom withone proton and no neutrons has a mass number of 1. Its nameis hydrogen-1. Hydrogen-2 has one proton and one neutron.The carbon isotope with a mass number of 12 is called carbon-12. If you know that the atomic number for carbon is6, you can calculate the number of neutrons in carbon-12 bysubtracting the atomic number from the mass number. Forcarbon-12, the number of neutrons is 12 6, or 6.

12 Mass number6 Number of protons (atomic number)

6 Number of neutrons

Calculating the Mass of an ElementMost elements found in nature contain a mixture of two ormore stable (nonradioactive) isotopes. For example, all copperis composed of copper-63 atoms and copper-65 atoms. Theterm atomic mass describes the mass of a mixture of isotopes.Atomic mass is the weighted average of the masses of all thenaturally occurring isotopes of an element. A weighted aver-age accounts for the percentages of each isotope that are pres-ent. Copper, including the copper in the Statue of Liberty(shown in Figure 16), is 69 percent copper-63 and 31 percentcopper-65. The atomic mass of copper is 63.6 amu. You cantry your hand at calculating atomic mass by doing theMathBreak at left.

Chapter 11292

Figure 16 The copper usedto make the Statue of Libertyincludes both copper-63 andcopper-65. Copper’s atomicmass is 63.6 amu.

Atomic MassTo calculate the atomic massof an element, multiply themass number of each isotopeby its percentage abundancein decimal form. Then addthese amounts together tofind the atomic mass. Forexample, chlorine-35 makesup 76 percent (its percent-age abundance) of all thechlorine in nature, andchlorine-37 makes up theother 24 percent. The atomicmass of chlorine is calculatedas follows:

Now It’s Your TurnCalculate the atomic mass ofboron, which occurs naturallyas 20 percent boron-10 and80 percent boron-11.

MATH BREAK

(35 0.76) 26.6(37 0.24) 8.9

35.5 amu

Draw diagrams of hydrogen-2,helium-3, and carbon-14.Show the correct number andlocation of each type of parti-cle. For the electrons, simplywrite the total number ofelectrons in the electroncloud. Use colored pencils ormarkers to represent the pro-tons, neutrons, and electrons.



What Forces Are at Work in Atoms?You have seen how atoms are composed of protons, neutrons,and electrons. But what are the forces (the pushes or pullsbetween two objects) acting between these particles? Four basicforces are at work everywhere, including within the atom—gravity, the electromagnetic force, the strong force, and theweak force. These forces are discussed below.


1. List the charge, location, and mass of a proton, a neutron,and an electron.

2. Determine the number of protons, neutrons, and elec-trons in an atom of aluminum-27.

3.Doing Calculations The metal thallium occurs natu-rally as 30 percent thallium-203 and 70 percent thallium-205. Calculate the atomic mass of thallium.

REVIEW

Weak Force The weak force is an important force in radioactive atoms.In certain unstable atoms, a neutron can change into a proton and anelectron. The weak force plays a key role in this change.

Strong Force Protons push away from one another because of the electromagnetic force. A nucleus containing two or more protonswould fly apart if it were not for the strong force. At the close distances between protons in the nucleus, the strong force is greaterthan the electromagnetic force, so the nucleus stays together.

Electromagnetic Force As mentioned earlier, objects that have the same charge repel each other, while objects with opposite charge attract each other. This is due to the electromagnetic force. Protons and electrons are attracted to each other because they have opposite charges. The electromagnetic force holds the electrons around the nucleus.

Gravity Probably the most familiar of the four forces is gravity. Gravityacts between all objects all the time. The amount of gravity betweenobjects depends on their masses and the distance between them. Gravitypulls objects, such as the sun, Earth, cars, and books, toward one another.However, because the masses of particles in atoms are so small, the force of gravity within atoms is very small.

Particles with the samecharges repel each other.

Particles with oppositecharges attract each other.

Forces in the Atom

NSTA

TOPIC: Inside the Atom, IsotopesGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP265, HSTP270

Chapter 11294

SECTION 1

Skills Check

Vocabularyatom (p. 280)

theory (p. 280)

electrons (p. 283)

model (p. 283)

nucleus (p. 285)

electron clouds (p. 286)

Section Notes

• Atoms are the smallest parti-cles of an element that retainthe properties of the element.

• In ancient Greece,Democritus argued thatatoms were the smallest particles in all matter.

• Dalton proposed an atomictheory that stated the follow-ing: Atoms are small particlesthat make up all matter;atoms cannot be created,divided, or destroyed; atomsof an element are exactlyalike; atoms of different el-ements are different; andatoms join together to makenew substances.

• Thomson discovered elec-trons. His plum-puddingmodel described the atom asa lump of positively chargedmaterial with negative elec-trons scattered throughout.

• Rutherford discovered thatatoms contain a small, dense,positively charged centercalled the nucleus.

• Bohr suggested that electronsmove around the nucleus atonly certain distances.

• According to the currentatomic theory, electronclouds are where electronsare most likely to be in thespace around the nucleus.

Math ConceptsATOMIC MASS The atomic mass of an elementtakes into account the mass of each isotope andthe percentage of the element that exists as thatisotope. For example, magnesium occurs natu-rally as 79 percent magnesium-24, 10 percentmagnesium-25, and 11 percent magnesium-26.The atomic mass is calculated as follows:

(24 0.79) 19.0(25 0.10) 2.5(26 0.11) 2.8

24.3 amu

Visual UnderstandingATOMIC MODELSThe atomic theory haschanged over the pastseveral hundred years. Tounderstand the differentmodels of the atom, lookover Figures 2, 4, 6, 8, and 9.

PARTS OF THE ATOM Atoms are composed ofprotons, neutrons, and electrons. To review theparticles and their placement in the atom,study Figure 11 on page 288.

Chapter Highlights


295Introduction to Atoms

SECTION 2

Vocabularyprotons (p. 288)

atomic mass unit (p. 288)

neutrons (p. 288)

atomic number (p. 290)

isotopes (p. 290)

mass number (p. 291)

atomic mass (p. 292)

Section Notes

• A proton is a positivelycharged particle with a massof 1 amu.

• A neutron is a particle withno charge that has a mass of1 amu.

• An electron is a negativelycharged particle with anextremely small mass.

• Protons and neutrons makeup the nucleus. Electrons arefound in electron clouds out-side the nucleus.

• The number of protons inthe nucleus of an atom is theatomic number. The atomicnumber identifies the atomsof a particular element.

• Isotopes of an atom have thesame number of protons buthave different numbers ofneutrons. Isotopes sharemost of the same chemicaland physical properties.

• The mass number of an atomis the sum of the atom’s neu-trons and protons.

• The atomic mass is an aver-age of the masses of all naturally occurring isotopesof an element.

• The four forces at work in anatom are gravity, the electro-magnetic force, the strongforce, and the weak force.

LabsMade to Order (p. 676)


TOPIC: Development of the Atomic Theory sciLINKS NUMBER: HSTP255

TOPIC: Modern Atomic Theory sciLINKS NUMBER: HSTP260

TOPIC: Inside the Atom sciLINKS NUMBER: HSTP265

TOPIC: Isotopes sciLINKS NUMBER: HSTP270



KEYWORD: HSTATS



The statements below are false. For each state-ment, replace the underlined word to make atrue statement.

1. Electrons are found in the nucleus of anatom.

2. All atoms of the same element containthe same number of neutrons.

3. Protons have no electric charge.

4. The atomic number of an element is thenumber of protons and neutrons in thenucleus.

5. The mass number is an average of themasses of all naturally occurring isotopesof an element.


Multiple Choice

6. The discovery of which particle provedthat the atom is not indivisible?a. proton c. electronb. neutron d. nucleus

7. In his gold foil experiment, Rutherfordconcluded that the atom is mostly emptyspace with a small, massive, positivelycharged center becausea. most of the particles passed straight

through the foil.b. some particles were slightly deflected.c. a few particles bounced back.d. All of the above

8. How many protons does an atom with anatomic number of 23 and a mass numberof 51 have?a. 23 c. 51b. 28 d. 74

9. An atom has no overall charge if it con-tains equal numbers ofa. electrons and protons.b. neutrons and protons.c. neutrons and electrons.d. None of the above

10. Which statement about protons is true?a. Protons have a mass of 1/1,840 amu.b. Protons have no charge.c. Protons are part of the nucleus of an

atom.d. Protons circle the nucleus of an atom.

11. Which statement about neutrons is true?a. Neutrons have a mass of 1 amu.b. Neutrons circle the nucleus of an atom.c. Neutrons are the only particles that

make up the nucleus.d. Neutrons have a negative charge.

12. Which of the following determines theidentity of an element?a. atomic number c. atomic massb. mass number d. overall charge

13. Isotopes exist because atoms of the sameelement can have different numbers ofa. protons. c. electrons.b. neutrons. d. None of the above

Short Answer

14. Why do scientific theories change?

15. What force holds electrons in atoms?

16. In two or three sentences, describe theplum-pudding model of the atom.


Concept Mapping

17. Use the followingterms to create a concept map: atom,nucleus, protons,neutrons, electrons,isotopes, atomic num-ber, mass number.


18. Particle accelerators, like the one shownbelow, are devices that speed up chargedparticles in order to smash them together.Sometimes the result of the collision is anew nucleus. How can scientists deter-mine whether the nucleus formed is thatof a new element or that of a new isotopeof a known element?

19. John Dalton made a number of state-ments about atoms that are now knownto be incorrect. Why do you think hisatomic theory is still found in sciencetextbooks?

MATH IN SCIENCE

20. Calculate the atomic mass of gallium consisting of 60 percent gallium-69 and40 percent gallium-71.

21. Calculate the number of protons, neu-trons, and electrons in an atom of zirconium-90, which has an atomicnumber of 40.


22. Study the models below, and answer thequestions that follow:

a. Which models represent isotopes of thesame element?

b. What is the atomic number for (a)?c. What is the mass number for (b)?

23. Predict how the direction of the movingparticle in the figure below will change,and explain what causes the change tooccur.

Key

Proton

Neutron

Electron

a b

c

297Introduction to Atoms



ReadingCheck-up


P H Y S I C A L S C I E N C E • A S T R O N O M Y

Water on the Moon?

298

When the astronauts of the Apollo space missionexplored the surface of the moon in 1969, allthey found was rock powder. None of the manysamples of moon rocks they carried back toEarth contained any hint of water. Because theastronauts didn’t see water on the moon andscientists didn't detect any in the lab, scientistsbelieved there was no water on the moon.

Then in 1994, radio waves suggested anotherpossibility. On a 4-month lunar jaunt, anAmerican spacecraft called Clementine beamedradio waves toward various areas of the moon,including a few craters that never receive sun-light. Mostly, the radio waves were reflected bywhat appeared to be ground-up rock. However,in part of one huge, dark crater, the radiowaves were reflected as if by . . . ice.

Hunting for Hydrogen AtomsScientists were intrigued by Clementine’sevidence. Two years later, another spacecraft,Lunar Prospector, traveled to the moon. Insteadof trying to detect water with radio waves,Prospector scanned the moon’s surface with adevice called a neutron spectrometer (NS). Aneutron spectrometer counts the number ofslow neutrons bouncing off a surface. When aneutron hits something about the same massas itself, it slows down. As it turns out, the onlything close to the mass of a neutron is an atomof the lightest of all elements, hydrogen. Sowhen the NS located high concentrations ofslow-moving neutrons on the moon, it indi-cated to scientists that the neutrons werecrashing into hydrogen atoms.

As you know, water consists of two atoms ofhydrogen and one atom of oxygen. The presenceof hydrogen atoms on the moon is more evi-dence that water may exist there.

How Did It Get There?Some scientists speculate that the water mol-ecules came from comets (which are 90 per-cent water) that hit the moon more than 4 billion years ago. Water from comets mayhave landed in the frigid, shadowed craters ofthe moon, where it mixed with the soil andfroze. The Aitken Basin, at the south pole of themoon, where much of the ice was detected, ismore than 12 km deep in places. Sunlightnever touches most of the crater. And it is verycold—temperatures there may fall to 229C.The conditions seem right to lock water intoplace for a very long time.

Think About Lunar Life Do some research on conditions on themoon. What conditions would humans have toovercome before we could establish a colonythere?

The Lunar Prospector spacecraft may havefound water on the moon.


299

M elissa Franklin is an experimental physicist. “I am trying tounderstand the forces that describe how everything in the

world moves—especially the smallest things,” she explains. “I wantto find the things that make up all matter in the universe and thentry to understand the forces between them.”

Other scientists rely on her to test some of the most importanthypotheses in physics. For instance, Franklin and her team recentlycontributed to the discovery of a particle called the top quark.(Quarks are the tiny particles that make up protons and neutrons.)

Physicists had theorized that the top quark might exist but hadno evidence. Franklin and more than 450 other scientists workedtogether to prove the existence of the top quark. Finding itrequired the use of a massive machine called a particle accelerator.Basically, a particle accelerator smashes particles together, and thenscientists look for the remains of the collision. The physicists had tobuild some very complicated machines to detect the top quark, butthe discovery was worth the effort. Franklin and the otherresearchers have earned the praise of scientists all over the world.

Getting Her Start“I didn’t always want to be a scientist, but what happens is thatwhen you get hooked, you really get hooked. The next thing youknow, you’re driving forklifts and using overhead cranes while at

In the course of a single day, you could find MelissaFranklin operating a hugedrill, giving a tour of her lab toa 10-year-old, putting togethera gigantic piece of electronicequipment, or even telling ajoke. Then you’d see her reallyget down to business—studying the smallest particlesof matter in the universe.

EXPERIMENTAL

the same time working on really tiny, incrediblycomplicated electronics. What I do is a combinationof exciting things. It’s better than watching TV.”

It isn’t just the best students who grow up to bescientists. “You can understand the ideas withouthaving to be a math genius,” Franklin says. Anyonecan have good ideas, she says, absolutely anyone.

Don’t Be Shy! Franklin also has some good advice for youngpeople interested in physics. “Go and bug peopleat the local university. Just call up a physics personand say, ‘Can I come visit you for a couple ofhours?’ Kids do that with me, and it’s really fun.”Why don't you give it a try? Prepare for the visit bymaking a list of questions you would like answered.

This particle accelerator was used inthe discovery of the top quark.


300 Chapter 12

Arranging the Elements. . . . . . . . . . . 302

QuickLab . . . . . . . . . . 307Apply . . . . . . . . . . . . . 308Internet Connection . . 309

Grouping the Elements. . . . . . . . . . . 310

Internet Connect . . . . 313Environment

Connection . . . . . . . . 314

Chapter Review . . . . . . . . . 320


LabBook . . . . . . . . . . . 678–679

The PeriodicTableThe PeriodicTable

A building as a Piece of Art!Would you believe that this strange-looking building is anart museum? It is! It’s the Guggenheim Museum in Bilbao,Spain. The building is made of limestone blocks, glass, andthe element titanium. Titanium was chosen because it isstrong, lightweight, and very resistant to corrosion andrust. In fact, the half-millimeter-thick fish-scale titaniumpanels covering most of the building are guaranteed to last100 years! In this chapter, you will learn about some otherelements on the periodic table and their properties.


1. How are elements organized in the periodictable?

2. Why is the table of the elements called “periodic”?

3. What one property isshared by elements in a group?


301

PLACEMENT PATTERN In this activity, you will determinethe pattern behind a new seatingchart your teacher has created.

Procedure

1. In your ScienceLog, draw a seatingchart for the classroom arrange-ment given to you by your teacher.Write the name of each of yourclassmates in the correct place onthe chart.

2. Write information about yourself,such as your name, date of birth,hair color, and height, in the spacethat represents you on the chart.

3. Starting with the people aroundyou, gather the same informationabout them. Write each person’sinformation in the proper space onthe seating chart.

Analysis

4. In your ScienceLog, identify a pat-tern to the information you gath-ered that might explain the orderof the people in the seating chart.If you cannot find a pattern, collectmore information and look again.

5. Test your pattern by gatheringinformation from a person you didnot talk to before.

6. If the new information does notsupport your pattern, reanalyze yourdata and collect more informationto determine another pattern.

The Periodic TableCopyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 12302

Arranging the ElementsImagine you go to a new grocery store to buy a box of cereal.You are surprised by what you find. None of the aisles arelabeled, and there is no pattern to the products on the shelves!You think it might take you days to find your cereal.

Some scientists probably felt a similar frustration before1869. By that time, more than 60 elements had been discoveredand described. However, it was not until 1869 that the el-ements were organized in any special way.

Discovering a PatternIn the 1860s, a Russian chemist named Dmitri Mendeleevbegan looking for patterns among the properties of the

elements. He wrote the names and properties of the elements on pieces of paper. He included density, appear-

ance, atomic mass, melting point, and informationabout the compounds formed from the element. He

then arranged and rearranged the pieces of paper, asshown in Figure 1. After much thought and work,

he determined that there was a repeatingpattern to the properties of the elements

when the elements were arranged inorder of increasing atomic mass.

The Properties of Elements Are Periodic Mendeleev sawthat the properties of the elements were periodic, meaning theyhad a regular, repeating pattern. Many things that are famil-iar to you are periodic. For example, the days of the week areperiodic because they repeat in the same order every 7 days.

When the elements were arranged in order of increasingatomic mass, similar chemical and physical properties wereobserved in every eighth element. Mendeleev’s arrangementof the elements came to be known as a periodic table becausethe properties of the elements change in a periodic way.

Section

1

periodic periodperiodic law group

Describe how elements arearranged in the periodic table.

Compare metals, nonmetals, and metalloids based on theirproperties and on their locationin the periodic table.

Describe the difference betweena period and a group.

Figure 1 By playing “chemical solitaire”on long train rides, Mendeleev organizedthe elements according to their properties.



Predicting Properties of Missing Elements Look at thesection of Mendeleev’s periodic table shown in Figure 2. Noticethe question marks. Mendeleev recognized that there were el-ements missing and boldly predicted that elements yet to bediscovered would fill the gaps. He also predicted the propertiesof the missing elements by using the pattern of properties inthe periodic table. When one of the missing elements, gal-lium, was discovered a few years later, its properties matchedMendeleev’s predictions very well. Since that time, all of themissing elements on Mendeleev’s periodic table have been dis-covered. In the chart below, you can see Mendeleev’s predic-tions for another missing element—germanium—and the actualproperties of that element.

Changing the ArrangementMendeleev noticed that a few elements in the table were notin the correct place according to their properties. He thoughtthat the calculated atomic masses were incorrect and that moreaccurate atomic masses would eventually be determined.However, new measurements of the atomic masses showedthat the masses were in fact correct.

The mystery was solved in 1914 by a British scientist namedHenry Moseley (MOHZ lee). From the results of his experi-ments, Moseley was able to determine the number of pro-tons—the atomic number—in an atom. When he rearrangedthe elements by atomic number, every element fell into itsproper place in an improved periodic table.

Since 1914, more elements have been discovered. Each dis-covery has supported the periodic law, considered to be thebasis of the periodic table. The periodic law states that thechemical and physical properties of elements are periodicfunctions of their atomic numbers. The modern version of theperiodic table is shown on the following pages.

The Periodic Table 303

Figure 2 Mendeleev used ques-tion marks to indicate someelements that he believed would later be identified.

Moseley was 26 when hemade his discovery. Hiswork allowed him to predictthat only three elementswere yet to be foundbetween aluminum andgold. The following year, ashe fought for the British inWorld War I, he was killed inaction at Gallipoli, Turkey.The British government nolonger assigns scientists tocombat duty.

Properties of Germanium

Mendeleev’s Actual predictions properties

Atomic mass 72 72.6

Density 5.5 g/cm3 5.3 g/cm3

Appearance dark gray metal gray metal

Melting point high melting point 937C


140.1

232.0

140.9

231.0

144.2

238.0

(144.9)

(237.0)

150.4

244.1

6.9

23.0

39.1

85.5

132.9

(223.0)

9.0

24.3

40.1

87.6

137.3

(226.0)

45.0

88.9

138.9

(227.0)

47.9

91.2

178.5

(261.1)

50.9

92.9

180.9

(262.1)

52.0

95.9

183.8

(263.1)

54.9

(97.9)

186.2

(262.1)

55.8

101.1

190.2

(265)

58.9

102.9

192.2

(266)

1.0

Praseodymium

Rutherfordium

Molybdenum

Lithium

Sodium

Potassium

Rubidium

Cesium

Francium

Cerium

Thorium Protactinium

Neodymium

Uranium

Promethium

Neptunium

Samarium

Plutonium

Beryllium

Magnesium

Calcium

Strontium

Barium

Radium

Scandium

Yttrium

Lanthanum

Actinium

Titanium

Zirconium

Hafnium

Vanadium

Niobium

Tantalum

Dubnium

Chromium

Tungsten

Seaborgium

Manganese

Technetium

Rhenium

Bohrium

Iron

Ruthenium

Osmium

Hassium

Cobalt

Rhodium

Iridium

Meitnerium

Hydrogen

Li

V

Na

K

Rb

Cs

Fr

Be

Mg

Ca

Sr

Ba

Ra

Sc

Y

La

Ac

Ti

Zr

H f

Rf

Nb

Ta

Db

Cr

Mo

W

Sg

Mn

Re

Bh

IrOs

Ce

Th

Pr

Pa

Nd

U

Pm

Np

Sm

Pu

Fe

Ru

Hs

Co

Rh

Mt

H

Tc

3

11

19

37

55

87

58

90

59

91

60

92

61

93

62

94

4

12

20

38

56

88

21

39

57

89

22

40

72

104

23

41

73

105

24

42

74

106

25

43

75

107

26

44

76 77

108

27

45

109

1

Group 3 Group 4 Group 5 Group 6 Group 7 Group 8 Group 9

Group 1 Group 2

Period 1

Period 2

Period 3

Period 4

Period 5

Period 6

Period 7

Lanthanides

Actinides

Background

Metals

Metalloids

Nonmetals

Chemical symbol

Solid

Liquid

Gas

6

CCarbon

12.0

Periodic Tableof the ElementsEach square on the table includes anelement’s name, chemical symbol,atomic number, and atomic mass.

Atomic number

Chemical symbol

Element name

Atomic mass

Chapter 12304

The color of the chemicalsymbol indicates the physi-cal state at room tempera-ture. Carbon is a solid.

The background colorindicates the type ofelement. Carbon is anonmetal.

A column of el-ements is called a group or family.

A row of elements iscalled a period.

These elements are placed below thetable to allow the table to be narrower.

Background

Metals

Metalloids

Nonmetals

Chemical symbol

Solid

Liquid

Gas

152.0

(243.1)

157.3

(247.1)

158.9

(247.1)

162.5

(251.1)

164.9

(252.1)

167.3

(257.1)

168.9

(258.1)

173.0

(259.1)

175.0

(262.1)

58.7 63.5 65.4 69.7 72.6 74.9 79.0 79.9 83.8

27.0 28.1 31.0 32.1 35.5 39.9

10.8 12.0 14.0 16.0 19.0 20.2

4.0

106.4 107.9 112.4 114.8 118.7 121.8 127.6 126.9 131.3

195.1

(271) (272)

197.0 200.6 204.4 207.2 209.0 (209.0) (210.0) (222.0)

(277)

Europium

Americium

Gadolinium

Curium

Terbium

Berkelium

Dysprosium

Californium

Holmium

Einsteinium

Erbium

Fermium

Thulium

Mendelevium

Ytterbium

Nobelium

Lutetium

Lawrencium

Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton

Aluminum Silicon Phosphorus Sulfur Chlorine Argon

Boron Carbon Nitrogen Oxygen Fluorine Neon

Helium

Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon

Ununnilium Unununium

Platinum Gold Mercury Thallium Lead Bismuth Polonium Astatine Radon

Ununbium

Eu

Am

Gd

Cm

Tb

Bk

Dy

Cf

Pd Ag Cd In Sn Sb Te I Xe

Pt

Uun Uuu

Au Hg Tl Pb Bi Po At Rn

Ho

Es

Er

Fm

Tm

Md

Yb

No

Lu

Lr

Ni Cu Zn Ga Ge As Se Br Kr

Al Si P S Cl Ar

B C N O F Ne

He

Uub

28 29 30 31 32 33 34 35 36

13 14 15 16 17 18

5 6 7 8 9 10

2

46 47 48 49 50 51 52 53 54

78 79 80 81 82 83 84 85 86

110 111

63

95

64

96

65

97

66

98

67

99

68

100

69

101

70

102

71

103

112

Group 13 Group 14 Group 15 Group 16 Group 17

Group 18

Group 10 Group 11 Group 12


A number in parentheses is the mass numberof the most stable isotope of that element.

The names and symbols of elements 110–112 aretemporary. They are based on the atomic number ofthe element. The official name and symbol will beapproved by an international committee of scientists.

This zigzag linereminds you wherethe metals, nonmetals,and metalloids are.

TOPIC: Periodic TableGO TO: go.hrw.comKEYWORD: HN0 Periodic

Visit the HRW Web site to see the most recent version of the periodic table.


Finding Your Way Around the Periodic TableAt first glance, you might think studying the periodic table islike trying to explore a thick jungle without a guide—it wouldbe easy to get lost! However, the table itself contains a lot ofinformation that will help you along the way.

Classes of Elements Elements are classified as metals,nonmetals, and metalloids, according to their properties. Thenumber of electrons in the outer energy level of an atomalso helps determine which category an element belongs in.The zigzag line on the periodic table can help you recog-nize which elements are metals, which are nonmetals, andwhich are metalloids.

Most elements are metals. Metals arefound to the left of the zigzag line on theperiodic table. Atoms of most metalshave few electrons in their outer energylevel, as shown at right.

Most metals are solid at room tem-perature. Mercury, however, is a liquid.Some additional information on propertiesshared by most metals is shown below.

Metals

A model of amagnesium atom

Most metals are malleable, meaningthat they can be flattened with a hammer without shattering.Aluminum is flattened into sheets to make cans and foil.

306

Most metals are ductile,which means that they can be drawn into thin wires. Allmetals are good conductors of electric current. The wires in the electrical devices in your home are made from the metal copper.

Chapter 12

Metals tend to be shiny. Youcan see a reflection in a mirrorbecause light reflects off theshiny surface of a thin layer of silver behind the glass.

Most metals are goodconductors of thermalenergy. This iron griddleconducts thermal energyfrom a stovetop to cookyour favorite foods.




Nonmetals are found to the right of thezigzag line on the periodic table. Atoms ofmost nonmetals have an almost completeset of electrons in their outer level, asshown at right. (Atoms of one group ofnonmetals, the noble gases, have a com-plete set of electrons, with most havingeight electrons in their outer energy level.)

More than half of the nonmetals aregases at room temperature. The prop-erties of nonmetals are the opposite ofthe properties of metals, as shown below.

Nonmetals

Metalloids, also called semiconductors,are the elements that border the zigzagline on the periodic table. Atoms of met-alloids have about a half-complete set ofelectrons in their outer energy level, asshown at right.

Metalloids have some properties ofmetals and some properties of nonmetals,as shown below.

Metalloids

A model of asilicon atom

A model of achlorine atom

Nonmetals are not malleable or ductile. In fact, solid nonmetals, like carbon (shown here in the graphite of the pencil lead), are brittle and will break or shatter when hit with a hammer.

Tellurium is shiny, but it is also brittleand is easily smashed into a powder.

Boron is almost ashard as diamond, butit is also very brittle.At high temperatures,boron is a goodconductor of electriccurrent.

Sulfur, like most nonmetals,is not shiny.

Nonmetals are poor conductorsof thermal energy and electriccurrent. If the gap in a sparkplug is too wide, the non-

metals nitrogen and oxygen in the air will stop the spark,

and a car’s engine will not run.

Conduction Connection

1. Fill a plastic-foamcup with hot water.

2. Stand a piece ofcopper wire and agraphite lead froma mechanical pencil in thewater.

3. After 1 minute, touch thetop of each object. Recordyour observations.

4. Which material conductedthermal energy the best?Why?

Each Element Is Identified by a Chemical Symbol Eachsquare on the periodic table contains information about anelement, including its atomic number, atomic mass, name, andchemical symbol. An international committee of scientists isresponsible for approving the names and chemical symbols ofthe elements. The names of the elements come from manysources. For example, some elements are named after impor-tant scientists (mendelevium, einsteinium), and others arenamed for geographical regions (germanium, californium).

The chemical symbol for each element usually consists ofone or two letters. The first letter in the symbol is always cap-italized, and the second letter, if there is one, is always writ-ten in lowercase. The chart below lists the patterns that thechemical symbols follow, and the Activity will help you inves-tigate two of those patterns further.

Chapter 12308

Writing the Chemical Symbols

You can create your own well-rounded periodic table using

coins, washers, and buttons onpage 678 of the LabBook.

Pattern of chemical symbols

first letter of the name

first two letters of the name

first letter and third or laterletter of the name

letter(s) of a word other thanthe English name

first letter of root words thatstand for the atomic number(used for elements whose offi-cial names have not yet beenchosen)

Examples

S—sulfur

Ca—calcium

Mg—magnesium

Pb—lead (from the Latinplumbum, meaning “lead”)

Uun—ununnilium (uhn uhn NIL ee uhm) (foratomic number 110)

Draw a line down a sheet of paper to divide it into twocolumns. Look at the el-ements with atomic numbers1 through 10 on the periodictable. Write all the chemicalsymbols and names that fol-low one pattern in one col-umn on your paper and allchemical symbols and namesthat follow a second patternin the second column. Writea sentence describing eachpattern you found.

One Set of SymbolsLook at the periodic table shown here.How is it the same as the periodictable you saw earlier? How is it differ-ent? Explain why it is important forscientific communication that thechemical symbols used are the samearound the world.



Rows Are Called Periods Each horizontal row of elements(from left to right) on the periodic table is called a period. Forexample, the row from lithium (Li) to neon (Ne) is Period 2. A row is called a period because the properties of elementsin a row follow a repeating, or periodic, pattern as you move across each period. The physical and chemical prop-erties of elements, such as conductivity and the number ofelectrons in the outer level of atoms, change gradually fromthose of a metal to those of a nonmetal in each period, asshown in Figure 3.

Columns Are Called Groups Each column of elements(from top to bottom) on the periodic table is called a group.Elements in the same group often have similar chemical andphysical properties. For this reason, sometimes a group is alsocalled a family. You will learn more about each group in thenext section.

Figure 3 The elements in a row become lessmetallic from left to right.

1. Compare a period and a group on the periodic table.

2. How are the elements arranged in the modern periodictable?

3. Comparing Concepts Compare metals, nonmetals, andmetalloids in terms of their electrical conductivity.


To remember that a periodgoes from left to rightacross the periodic table,just think of reading a sen-tence. You read from left toright across the page untilyou come to a period.

REVIEW

Elements at the left end of aperiod, such as titanium, arevery metallic in their properties.

Elements farther to theright, like germanium, are less metallic in theirproperties.

Elements at the far right endof a period, such as bromine,are nonmetallic in their properties.

VK Ca Sc Ti Cr Mn Fe Co19 20 21 22 23 24 25 26 27

Ni Cu Zn Ga Ge As Se Br Kr28 29 30 31 32 33 34 35 36

47.9Titanium

Ti22

72.6Germanium

Ge32

79.9Bromine

Br35

NSTA

TOPIC: The Periodic TableGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP280

Chapter 12310

Grouping the ElementsYou probably know a family with several members that looka lot alike. Or you may have a friend whose little brother orsister acts just like your friend. Members of a family often—but not always—have a similar appearance or behavior.Likewise, the elements in a family or group in the periodictable often—but not always—share similar properties. The prop-erties are similar because the atoms of the elements have thesame number of electrons in their outer energy level.

Groups 1 and 2: Very Reactive MetalsThe most reactive metals are the elements in Groups 1 and 2.What makes an element reactive? The answer has to do withelectrons in the outer energy level of atoms. Atoms will oftentake, give, or share electrons with other atoms in order to havea complete set of electrons in their outer energy level. Elementswhose atoms undergo such processes are reactive and combineto form compounds. Elements whose atoms need to take, give,or share only one or two electrons to have a filled outer leveltend to be very reactive.

The elements in Groups 1 and 2 are so reactive that theyare only found combined with other elements in nature. Tostudy the elements separately, the naturally occurringcompounds must first be broken apart through chemicalchanges.

Group 1: Alkali Metals

Alkali (AL kuh LIE) metals aresoft enough to be cut with aknife, as shown in Figure 4. Thedensities of the alkali metalsare so low that lithium,sodium, and potassium areactually less dense than water.

Group contains: MetalsElectrons in the outer level: 1Reactivity: Very reactiveOther shared properties: Soft; silver-colored; shiny;low density

Lithium

Sodium

Potassium

Rubidium

Cesium

Francium

Li

Na

K

Rb

Cs

Fr

3

11

19

37

55

87 Figure 4 Metals so soft thatthey can be cut with a knife?Welcome to the alkali metals.

Although the elementhydrogen appears above thealkali metals on the periodictable, it is not considered amember of Group 1. It willbe described separately at

the end of this section.

Section

2

alkali metalsalkaline-earth metalshalogensnoble gases

Explain why elements in a groupoften have similar properties.

Describe the properties of theelements in the groups of theperiodic table.



Alkali metals are the most reactive of the metals. This isbecause their atoms can easily give away the single electronin their outer level. For example, alkali metals react violentlywith water, as shown in Figure 5. Alkali metals are usuallystored in oil to prevent them from reacting with water andoxygen in the atmosphere.

The compounds formed from alkali metals have many uses.Sodium chloride (table salt) can be used to add flavor to yourfood. Sodium hydroxide can be used to unclog your drains.Potassium bromide is one of several potassium compoundsused in photography.

Group 2: Alkaline-earth Metals

Alkaline-earth metals are not as reactive as alkalimetals because it is more difficult for atoms to giveaway two electrons than to give away only onewhen joining with other atoms.

The alkaline-earth metal magnesium is oftenmixed with other metals to make low-densitymaterials used in airplanes. Compounds ofalkaline-earth metals also have many uses.For example, compounds of calcium arefound in cement, plaster, chalk, and evenyou, as shown in Figure 6.

Figure 5 As alkali metals react with water, they form hydrogen gas.

Group contains: MetalsElectrons in the outer level: 2Reactivity: Very reactive, but less reactive than alkalimetalsOther shared properties: Silver-colored; more densethan alkali metals

Beryllium

Magnesium

Calcium

Strontium

Barium

Radium

Be

Mg

Ca

Sr

Ba

Ra

4

12

20

38

56

88

Figure 6 Smile! Calcium, analkaline-earth metal, is animportant component of acompound that makes yourbones and teeth healthy.

311

Lithium PotassiumSodium


Groups 3–12: Transition Metals Groups 3–12 do not have individual names. Instead, thesegroups are described together under the name transition metals.

The atoms of transition metals do not give away their elec-trons as easily as atoms of the Group 1 and Group 2 metalsdo, making transition metals less reactive than the alkali metals and the alkaline-earth metals. The properties of thetransition metals vary widely, as shown in Figure 7.

Some transition metals, including the titanium in the artificial hip at right,are not very reactive. But others, suchas iron, are reactive. The iron in thesteel trowel above has reacted withoxygen to form rust.

Figure 7 Transition metals have a wide range of physical and chemical properties.

Chapter 12312

Group contains: MetalsElectrons in the outer level: 1 or 2Reactivity: Less reactive than alkaline-earth metalsOther shared properties: Shiny; good conductors of thermalenergy and electric current; higher densities and melting points(except for mercury) than elements in Groups 1 and 2

Self-CheckWhy are alkali metals more reactive than alkaline-earth metals? (See page 724 to check your answer.)

Rutherfordium

Molybdenum

Scandium

Yttrium

Lanthanum

Actinium

Titanium

Zirconium

Hafnium

Vanadium

Niobium

Tantalum

Dubnium

Chromium

Tungsten

Seaborgium

Manganese

Technetium

Rhenium

Bohrium

Iron

Ruthenium

Osmium

Hassium

Cobalt

Rhodium

Iridium

Meitnerium

VSc

Y

La

Ac

Ti

Zr

H f

Rf

Nb

Ta

Db

Cr

Mo

W

Sg

Mn

Re

Bh

IrOs

Fe

Ru

Hs

Co

Rh

Mt

Tc

21

39

57

89

22

40

72

104

23

41

73

105

24

42

74

106

25

43

75

107

26

44

76 77

108

27

45

109

Nickel Copper Zinc

Palladium Silver Cadmium


Platinum Gold Mercury

Ununbium

Pd Ag Cd

Pt

Uun Uuu

Au Hg

Ni Cu Zn

Uub

28 29 30

46 47 48

78 79 80

110 111 112

Mercury is used in thermometers because,unlike the other transition metals, it is inthe liquid state at room temperature.

Many transition metals aresilver-colored—but not all!This gold ring proves it!


Lanthanides and Actinides Some transitionmetals from Periods 6 and 7 are placed at the bot-tom of the periodic table to keep the table frombeing too wide. The properties of the elements ineach row tend to be very similar.

Elements in the first row are calledlanthanides because they follow thetransition metal lanthanum. The lan-thanides are shiny, reactive metals.Some of these elements are used tomake different types of steel. An impor-tant use of a compound of one lan-thanide element is shown in Figure 8.

Elements in the second row arecalled actinides because they follow thetransition metal actinium. All atoms ofactinides are radioactive, which meansthey are unstable. The atoms of aradioactive element can change intoatoms of a different element. Elementslisted after plutonium, element 94, donot occur in nature but are insteadproduced in laboratories. You mighthave one of these elements in yourhome. Very small amounts of americ-ium (AM uhr ISH ee uhm), element 95,are used in some smoke detectors.


1. What are two properties of the alkali metals?

2. What causes the properties of elements in a group to besimilar?

3. Applying Concepts Why are neither the alkali metals northe alkaline-earth metals found uncombined in nature?

REVIEW

138.9Lanthanum

La57

(227.0)Actinium

Ac89

58

90

59

91

60

92

61

93

62

94

Ce

Th

Pr

Pa

Nd

U

Pm

Np

Sm

Pu

Eu

Am

Gd

Cm

Tb

Bk

Dy

Cf

Ho

Es

Er

Fm

Tm

Md

Yb

No

Lu

Lr

63

95

64

96

65

97

66

98

67

99

68

100

69

101

70

102

71

103

Lanthanides

Actinides

Figure 8 Seeing red? The color red appears on acomputer monitor because of a compound formedfrom europium that coats the back of the screen.

NSTA

TOPIC: MetalsGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP285


Groups 13–16: Groups with MetalloidsMoving from Group 13 across to Group 16, the elements shiftfrom metals to nonmetals. Along the way, you find the met-alloids. These elements have some properties of metals andsome properties of nonmetals.

Group 13: Boron Group

The most common element from Group 13 is alu-minum. In fact, aluminum is the most abundantmetal in Earth’s crust. Until the 1880s, it was con-sidered a precious metal because the process usedto produce pure aluminum was very expensive. Infact, aluminum was even more valuable than gold,as shown in Figure 9.

Today, the process is not as difficult or expen-sive. Aluminum is now an important metal usedin making lightweight automobile parts and air-craft, as well as foil, cans, and wires.

Group 14: Carbon Group

The metalloids silicon and germanium are used tomake computer chips. The metal tin is usefulbecause it is not very reactive. A tin can is reallymade of steel coated with tin. The tin is less reac-tive than the steel, and it keeps the steel from rusting.

Chapter 12314

Group contains: One metalloid and four metalsElectrons in the outer level: 3Reactivity: ReactiveOther shared properties: Solid at room temperature

Gallium

Aluminum

Boron

Indium

Thallium

In

Tl

Ga

Al

B

31

13

5

49

81

Group contains: One nonmetal, two metalloids, andtwo metalsElectrons in the outer level: 4Reactivity: Varies among the elementsOther shared properties: Solid at room temperature

Germanium

Silicon

Carbon

Tin

Lead

Sn

Pb

Ge

Si

C

32

14

6

50

82

Figure 9 During the 1850s and 1860s, EmperorNapoleon III of France used aluminum dinnerwarebecause aluminum was more valuable than gold!

Recycling aluminum uses less energythan obtaining aluminum in the firstplace. Aluminum must be separatedfrom bauxite, a mixture containingnaturally occurring compounds of aluminum. Twenty times moreelectrical energy is required toseparate aluminum from bauxitethan to recycle used aluminum.



The nonmetal carbon can be founduncombined in nature, as shown in Figure 10.Carbon forms a wide variety of compounds.Some of these compounds, including pro-teins, fats, and carbohydrates, are essential tolife on Earth.

Group 15: Nitrogen Group

Nitrogen, which is a gas at room temperature,makes up about 80 percent of the air you breathe.Nitrogen removed from air is reacted with hydro-gen to make ammonia for fertilizers.

Although nitrogen is unreactive, phosphorus isextremely reactive, as shown in Figure 11. In fact,phosphorus is only found combined with otherelements in nature.

Group 16: Oxygen Group

Oxygen makes up about 20 percent of air. Oxygenis necessary for substances to burn, such as thechemicals on the match in Figure 11. Sulfur,another common member of Group 16, can befound as a yellow solid in nature. The principaluse of sulfur is to make sulfuric acid, the mostwidely used compound in the chemical industry.

Diamond is the hardest material known.It is used as a jewel and on cutting toolssuch as saws, drills, and files.

Figure 11Simply striking a matchon the side of this boxcauses chemicals onthe match to reactwith phosphorus on the box andbegin to burn.


Group contains: Two nonmetals, two metalloids, andone metalElectrons in the outer level: 5Reactivity: Varies among the elementsOther shared properties: All but nitrogen are solidat room temperature.

Arsenic

Phosphorus

Nitrogen

Antimony

Bismuth

Sb

Bi

As

P

N

33

15

7

51

83

Group contains: Three nonmetals, one metalloid,and one metalElectrons in the outer level: 6Reactivity: ReactiveOther shared properties: All but oxygen are solid atroom temperature.

Selenium

Sulfur

Oxygen

Tellurium

Polonium

Te

Po

Se

S

O

34

16

8

52

84

Soot—formed from burning oil, coal, and wood—is used as a pigment in paints and crayons.

Figure 10 Diamonds andsoot have very differentproperties, yet both arenatural forms of carbon.


Groups 17 and 18: Nonmetals OnlyThe elements in Groups 17 and 18 are nonmetals. The el-ements in Group 17 are the most reactive nonmetals, but theelements in Group 18 are the least reactive nonmetals. In fact,the elements in Group 18 normally won’t react at all withother elements.

Group 17: Halogens

Halogens are very reactive nonmetals because theiratoms need to gain only one electron to have acomplete outer level. The atoms of halogens com-bine readily with other atoms, especially metals,to gain that missing electron.

Although the chemical properties of the halo-gens are similar, the physical properties are quitedifferent, as shown in Figure 12.

Both chlorine and iodine are used as disinfec-tants. Chlorine is used to treat water, while iodinemixed with alcohol is used in hospitals.

Group 18: Noble Gases

Noble gases are unreactive nonmetals. Because theatoms of the elements in this group have a com-plete set of electrons in their outer level, they donot need to lose or gain any electrons. Therefore,they do not react with other elements under nor-mal conditions.

All of the noble gases are found in Earth’satmosphere in small amounts. Argon, the mostabundant noble gas in the atmosphere, makes upalmost 1 percent of the atmosphere.

Figure 12 Physical propertiesof some halogens at roomtemperature are shown here.

316

Group contains: NonmetalsElectrons in the outer level: 7Reactivity: Very reactiveOther shared properties: Poor conductors of electriccurrent; react violently with alkali metals to formsalts; never found uncombined in nature

Bromine

Chlorine

Fluorine

Iodine

Astatine

I

At

Br

Cl

F

35

17

9

53

85

Group contains: NonmetalsElectrons in the outer level: 8 (2 for helium)Reactivity: UnreactiveOther shared properties: Colorless, odorless gasesat room temperature

Krypton

Argon

Neon

Helium

Xenon

Radon

Xe

Rn

Kr

Ar

Ne

He

36

18

10

2

54

86

The term noble gasesdescribes the nonreactivityof these elements. Just asnobles, such as kings andqueens, did not often mixwith common people, thenoble gases do not normallyreact with other elements.

Chapter 12

Chlorine is a yellowishgreen gas.

Bromine is adark red liquid.

Iodine is a darkgray solid.

The nonreactivity of the noble gasesmakes them useful. Ordinary light bulbslast longer when filled with argon thanthey would if filled with a reactive gas.Because argon is unreactive, it does notreact with the metal filament in the lightbulb even when the filament gets hot.The low density of helium causes blimpsand weather balloons to float, and itsnonreactivity makes helium safer to usethan hydrogen. One popular use of noblegases that does not rely on their nonre-activity is shown in Figure 13.

Hydrogen Stands Apart

The properties of hydrogen do not match the properties of anysingle group, so hydrogen is set apart from the other elementsin the table.

Hydrogen is placed above Group 1 in the periodic tablebecause atoms of the alkali metals also have only one elec-tron in their outer level. Atoms of hydrogen, like atoms ofalkali metals, can give away one electron when joining withother atoms. However, hydrogen’s physical properties are morelike the properties of nonmetals than of metals. As you cansee, hydrogen really is in a group of its own.

Hydrogen is the most abundant element in the universe.Hydrogen’s reactive nature makes it useful as a fuel in rockets,as shown in Figure 14. Figure 14 Hydrogen reacts

violently with oxygen. The hotwater vapor that forms as aresult pushes the space shuttleinto orbit.


1. In which group are the unreactive nonmetals found?

2. What are two properties of the halogens?

3. Making Predictions In the future, a new halogen maybe synthesized. Predict its atomic number and properties.

4. Comparing Concepts Compare the element hydrogenwith the alkali metal sodium.

Figure 13 Besides neon, other noble gases are oftenused in “neon” lights.

Electrons in the outer level: 1Reactivity: ReactiveOther properties: Colorless, odorless gas at room tem-perature; low density; reacts explosively with oxygen

REVIEW

HydrogenH1

Argon producesa lavender color.

Xenon producesa blue color.

Neon produces anorange-red color.


Chapter Highlights

Chapter 12318

SECTION 1

Vocabularyperiodic (p. 302)

periodic law (p. 303)

period (p. 309)

group (p. 309)

Section Notes

• Mendeleev developed thefirst periodic table. Hearranged elements in order of increasing atomic mass. The properties of elementsrepeated in an orderly pat-tern, allowing Mendeleev to predict properties for el-ements that had not yet been discovered.

• Moseley rearranged the elements in order of increas-ing atomic number.

• The periodic law states thatthe chemical and physicalproperties of elements areperiodic functions of theiratomic numbers.

• Elements in the periodictable are divided into metals, metalloids, andnonmetals.

• Each element has a chemicalsymbol that is recognizedaround the world.

• A horizontal row of elementsis called a period. The el-ements gradually change from metallic to nonmetallicfrom left to right across eachperiod.

• A vertical column of elementsis called a group or family.Elements in a group usuallyhave similar properties.

LabsCreate a Periodic Table (p. 678)

Skills CheckVisual UnderstandingPERIODIC TABLE OF THE ELEMENTS Scientistsrely on the periodic table as a resource for alarge amount of information. Review theperiodic table on pages 304–305. Pay closeattention to the labels and the key; they will help you understand the informationpresented in the table.

CLASSES OF ELEMENTS Identifying an elementas a metal, nonmetal, or metalloid gives you abetter idea of the properties of that element.Review the figures on pages 306–307 tounderstand how to use thezigzag line on the periodictable to identify the classesof elements and to reviewthe properties of elementsin each category.


SECTION 2

Vocabularyalkali metals (p. 310)

alkaline-earth metals (p. 311)

halogens (p. 316)

noble gases (p. 316)

Section Notes

• The alkali metals (Group 1)are the most reactive metals.Atoms of the alkali metalshave one electron in theirouter level.

• The alkaline-earth metals(Group 2) are less reactivethan the alkali metals. Atomsof the alkaline-earth metalshave two electrons in theirouter level.

• The transition metals(Groups 3–12) include mostof the well-known metals aswell as the lanthanides andactinides located below theperiodic table.

• Groups 13–16 contain themetalloids along with somemetals and nonmetals. Theatoms of the elements ineach of these groups havethe same number of elec-trons in their outer level.

• The halogens (Group 17) arevery reactive nonmetals.Atoms of the halogens haveseven electrons in their outerlevel.

• The noble gases (Group 18)are unreactive nonmetals.Atoms of the noble gaseshave a complete set of elec-trons in their outer level.

• Hydrogen is set off by itselfbecause its properties do notmatch the properties of anyone group.


TOPIC: The Periodic Table sciLINKS NUMBER: HSTP280

TOPIC: Metals sciLINKS NUMBER: HSTP285

TOPIC: Metalloids sciLINKS NUMBER: HSTP290

TOPIC: Nonmetals sciLINKS NUMBER: HSTP295

TOPIC: Buckminster Fuller and the Buckyball sciLINKS NUMBER: HSTP300



KEYWORD: HSTPRT

The Periodic Table 319Copyright © by Holt, Rinehart and Winston. All rights reserved.


Complete the following sentences by choos-ing the appropriate term from each pair ofterms listed below.

1. Elements in the same vertical column inthe periodic table belong to the same ? . (group or period)

2. Elements in the same horizontal row inthe periodic table belong to the same ? . (group or period)

3. The most reactive metals are ? . (alkali metals or alkaline-earth metals)

4. Elements that are unreactive are called ? . (noble gases or halogens)


Multiple Choice

5. An element that is a very reactive gas ismost likely a member of thea. noble gases. c. halogens.b. alkali metals. d. actinides.

6. Which statement is true?a. Alkali metals are generally found in

their uncombined form.b. Alkali metals are Group 1 elements.c. Alkali metals should be stored under

water.d. Alkali metals are unreactive.

7. Which statement about the periodic tableis false?a. There are more metals than nonmetals.b. The metalloids are located in Groups 13

through 16.c. The elements at the far left of the table

are nonmetals.d. Elements are arranged by increasing

atomic number.

8. One property of most nonmetals is thatthey area. shiny.b. poor conductors of electric current.c. flattened when hit with a hammer.d. solids at room temperature.

9. Which is a true statement about elements?a. Every element occurs naturally.b. All elements are found in their uncom-

bined form in nature.c. Each element has a unique atomic

number.d. All of the elements exist in approxi-

mately equal quantities.

10. Which is NOT found on the periodictable?a. the atomic number of each elementb. the symbol of each elementc. the density of each elementd. the atomic mass of each element

Short Answer

11. Why was Mendeleev’s periodic table useful?

12. How is Moseley’s basis for arranging theelements different from Mendeleev’s?

13. How is the periodic table like a calendar?

14. Describe the location of metals, metal-loids, and nonmetals on the periodictable.


Concept Mapping

15. Use the followingterms to create aconcept map: peri-odic table, elements,groups, periods,metals, nonmetals,metalloids.


16. When an element with 115 protons in itsnucleus is synthesized, will it be a metal,a nonmetal, or a metalloid? Explain.

17. Look at Mendeleev’s periodic table inFigure 2. Why was Mendeleev not able tomake any predictions about the noble gaselements?

18. Your classmate offers to give you a pieceof sodium he found while hiking. What isyour response? Explain.

19. Determine the identity of each elementdescribed below:a. This metal is very reactive, has proper-

ties similar to magnesium, and is in thesame period as bromine.

b. This nonmetal is in the same group as lead.

c. This metal is the most reactive metal inits period and cannot be found uncom-bined in nature. Each atom of the el-ement contains 19 protons.

MATH IN SCIENCE

20. The chart below shows the percentages ofelements in the Earth’s crust.

Excluding the “Other” category, what per-centage of the Earth’s crust isa. alkali metals?b. alkaline-earth metals?


21. Study the diagram below to determine thepattern of the images. Predict the missingimage, and draw it. Identify which prop-erties are periodic and which propertiesare shared within a group.

?fpo

47-A

46.6% O

27.7% Si

2.0% Mg

2.8% Na

3.6% Ca

5.0% Fe

8.1% Al

2.6% K

1.6% Other

321The Periodic Table



ReadingCheck-up


322

The Science of Fireworks

What do the space shuttle and theFourth of July have in common? Thesame scientific principles that help

scientists launch a space shuttle also helppyrotechnicians create spectacular fireworksshows. The word pyrotechnics comes from theGreek words for “fire art.” Explosive and daz-zling, a fireworks display is both a science andan art.

An Ancient HistoryMore than 1,000 years ago, Chinese civilizationsmade black powder, the original gunpowderused in pyrotechnics. They used the powder toset off firecrackers and primitive missiles. Blackpowder is still used today to launch fireworksinto the air and to give fireworks an explosivecharge. Even the ingredients—saltpeter (potas-sium nitrate), charcoal, and sulfur—haven’tchanged since ancient times.

Snap, Crackle, Pop!The shells of fireworks contain the ingredientsthat create the explosions. Inside the shells,black powder and other chemicals are packedin layers. When ignited, one layer may cause abright burst of light while a second layer pro-duces a loud booming sound. The shell’s shapeaffects the shape of the explosion. Cylindricalshells produce a trail of lights that looks like anumbrella. Round shells produce a star-burstpattern of lights.

The color and sound of fireworks dependon the chemicals used. To create colors, chemi-cals like strontium (for red), magnesium (forwhite), and copper (for blue) can be mixedwith the gunpowder.

Explosion in the SkyFireworks are launched from metal, plastic, orcardboard tubes. Black powder at the bottomof the shell explodes and shoots the shell intothe sky. A fuse begins to burn when the shell islaunched. Seconds later, when the explosivechemicals are high in the air, the burning fuselights another charge of black powder. Thisignites the rest of the ingredients in the shell,causing an explosion that lights up the sky!

Bang for Your Buck The fireworks used during New Year’s Eveand Fourth of July celebrations can cost any-where from $200 to $2,000 apiece. Count thenumber of explosions at the next fireworksshow you see. If each of the fireworks cost just$200 to produce, how much would the fire-works for the entire show cost?

Cutaway view of a typicalfirework. Each shell createsa different type of display.

Quick-burning fuse

Time-delay fuse

Light-burst mixture

Fuse

Sound-burst mixture

Black-powder propellant


323

B U C K Y B A L LSResearchers are scrambling for the ball—thebuckyball, that is. This special form of carbonhas 60 carbon atoms linked together in a shapemuch like a soccer ball. Scientists are having afield day trying to find new uses for thisunusual molecule.

The Starting LineupNamed for architect Buckminster Fuller, bucky-balls resemble the geodesic domes that arecharacteristic of the architect’s work. Excitementover buckyballs began in 1985 when scientistsprojected light from a laser onto a piece ofgraphite. In the soot that remained, researchersfound a completely new kind of molecule!Buckyballs are also found in the soot from acandle flame. Some scientists claim to havedetected buckyballs in outer space. In fact, one

The buckyball, short for buckminster-fullerene, was named after architectBuckminster Fuller.

Potassium atom trappedinside buckyball

Carbonatoms

Bond

hypothesis suggests that buckyballs might be atthe center of the condensing clouds of gas, dust,and debris that form galaxies.

The Game Plan Ever since buckyballs were discovered, chemistshave been busy trying to identify the molecules’properties. One interesting property is that sub-stances can be trapped inside a buckyball. Abuckyball can act like a cage that surroundssmaller substances, such as individual atoms.Buckyballs also appear to be both slippery andstrong. They can be opened to insert materials,and they can even link together in tubes.

How can buckyballs be used? They mayhave a variety of uses, from carrying messagesthrough atom-sized wires in computer chips todelivering medicines right where the bodyneeds them. Making tough plastics and cuttingtools are uses that are also under investigation.With so many possibilities,scientists expect to geta kick out of bucky-balls for sometime!

The Kickoff A soccer ballis a great modelfor a buckyball.On the model, theplaces where threeseams meet correspondto the carbon atoms on a buckyball. What represents the bonds betweencarbon atoms? Does your soccer-ball modelhave space for all 60 carbon atoms? You’ll haveto count and see for yourself.


T I M E L I N E

U N I T Interactions ofMatter

Unit 5324

5n this unit you willstudy the inter-

actions through whichmatter can change itsidentity. You will learnhow atoms bond withone another to formcompounds and howatoms join in differentcombinations to formnew substancesthrough chemicalreactions. You will alsolearn about the prop-erties of several cate-gories of compounds.Finally, you will learnhow nuclear interac-tions can actuallychange the identity ofan atom. This timelineincludes some of theevents leading to thecurrent understandingof these interactions of matter.

I1828

Urea, a compound foundin urine, is produced in alaboratory. Until this time,

chemists had believedthat compounds createdby living organisms could

not be produced in the laboratory.

1858German chemistFriedrich August

Kekulé suggests thatcarbon forms four

chemical bonds andcan form longchains of car-bon bonded

to itself.

1964Dr. Martin Luther King, Jr.,

American civil rights leader, isawarded the Nobel Peace Prize.

1969The Nimbus III weather satellite

is launched by the UnitedStates, representing the first

civilian use of nuclear batteries.

1979Public fear about nuclear

power grows after an accidentoccurs at the Three Mile Island

nuclear power station, inPennsylvania.


1898The United States defeats Spain in

the Spanish-American War.

Marie Curie, Pierre Curie, and Henri Becquerel are

awarded the Nobel Prize inPhysics for the discovery

of radioactivity.

1996Evidence of organic compounds in

a meteorite leads scientists tospeculate that life may haveexisted on Mars more than

3.6 billion years ago. 2001The first total

solar eclipse ofthe millenium

occurs onJune 21.

1867Swedish chemist Alfred Nobeldevelops dynamite. Dynamite’sexplosive power is a result ofthe decomposition reaction

of nitroglycerin.

1942

The first nuclear chain reaction iscarried out in a squash court

under the football stadium at theUniversity of Chicago.

1903

325Interactions of MatterCopyright © by Holt, Rinehart and Winston. All rights reserved.

326 Chapter 13

Electrons and Chemical Bonding . . . . 328


Types of ChemicalBonds . . . . . . . . . . . . . 332

MathBreak . . . . . . . . . 334Biology Connection . . 339QuickLab . . . . . . . . . . 340Apply . . . . . . . . . . . . . 341Internet Connect . . . . 341

Chapter Review . . . . . . . . . . 344


LabBook . . . . . . . . . . . 680–681

ChemicalBondingChemicalBonding

Bonded for LifeLook at the photo. What looks like a fantastic modern art“sculpture” is actually a model of DNA, one of the longestand most complex molecules in living things. In DNA, twovery long spiral strands of atoms bond together, forming a double spiral. The DNA in living cells contains all thecoding for passing on the traits of that cell and that organism to each new cell as it is formed. In this chapter,you will learn how atoms bond in different ways duringchemical reactions.


1. What is a chemical bond?2. How are ionic bonds dif-

ferent from covalentbonds?

3. How are the properties ofmetals related to thetype of bonds in them?


327

FROM GLUE TO GOOPParticles of glue can bond to otherparticles and hold objects together.Different types of bonds create differences in the properties of sub-stances. In this activity, you will seehow the formation of bonds causesan interesting change in the proper-ties of white glue.

Procedure

1. Fill a small paper cup full of white

Observe the properties of the glue, and recordyour observations.

2. Fill a second small paper cupfull of borax solution.

3. Pour the borax solution into thecup containing the white glue, andstir well using a plastic spoon.

4. When it becomes too thick to stir,remove the material from thecup and knead it with your fin-gers. Observe the properties ofthe material, and record yourobservations.

Analysis

5. Compare the properties of theglue with those of the new material.

6. The properties of the new mater-ial resulted from the bondsbetween the borax and the parti-cles of the glue. If too little boraxwere used, in what way wouldthe properties of the materialhave been different?

14

14

Chemical Bonding

glue.


Chapter 13328

Electrons and Chemical BondingHave you ever stopped to consider that by using just the 26letters of the alphabet, you make all of the words you useevery day? Even though the number of letters is limited, their

ability to be combined in different waysallows you to make an enormous number

of words. Now look around the room.

Everything around you—desks,chalk, paper, even your friends—

is made of atoms of elements.How can so many sub-stances be formed fromabout 100 elements? Inthe same way that wordscan be formed by com-

bining letters, differentsubstances can be formedby combining atoms.

Atoms Combine Through Chemical BondingThe atoms of just three elements—carbon, hydrogen, andoxygen—combine in different patterns to form the sub-stances sugar, alcohol, and citric acid. Chemical bonding isthe joining of atoms to form new substances. The prop-erties of these new substances are different from those ofthe original elements. A force of attraction that holds twoatoms together is called a chemical bond. As you will see,chemical bonds involve the electrons in the atoms.

Atoms and the chemical bonds that connect them cannotbe observed with your eyes. During the past 150 years, scien-tists have performed many experiments that have led to thedevelopment of a theory of chemical bonding. Remember thata theory is a unifying explanation for a broad range of hypoth-eses and observations that have been supported by testing.The use of models helps people to discuss the theory of howand why atoms form chemical bonds.

Section

1

chemical bondingchemical bondvalence electrons

Describe chemical bonding. Identify the number of valence

electrons in an atom. Predict whether an atom is

likely to form bonds.

Why are the amino acids that arechemically bonded together to formyour proteins all left-handed? Readabout one cosmic explanation onpage 346.



Electron Number and OrganizationTo understand how atoms form chemical bonds, you first needto know how many electrons are in a particular atom and howthe electrons in an atom are organized. The number of elec-trons in an atom can be determined from the atomic numberof the element. The atomic number is the number of protonsin an atom. However, atoms have no charge, so the atomicnumber also represents the number of electrons in the atom.

The electrons in an atom are organized inenergy levels. The levels farther from thenucleus contain electrons that havemore energy than levels closer to thenucleus. The arrangement of elec-trons in a chlorine atom is shownin Figure 1.

Outer-Level Electrons Are the Key to Bonding As you justsaw in Figure 1, a chlorine atom has a total of 17 electrons.When a chlorine atom bonds to another atom, not all of theseelectrons are used to create the bond. Most atoms form bondsusing only the electrons in their outermost energy level. Theelectrons in the outermost energy level of an atom are calledvalence (VAY luhns) electrons. Thus, a chlorine atom has 7valence electrons. You can see the valence electrons for atomsof some other elements in Figure 2.

Chemical Bonding 329

Figure 1 Electron Arrangementin an Atom

Figure 2 Valence electrons are the electrons in theoutermost energy level of an atom.

a

b

OxygenElectron total: 8First level: 2 electronsSecond level: 6 electrons

SodiumElectron total: 11First level: 2 electronsSecond level: 8 electronsThird level: 1 electron

Electrons will enter the secondenergy level only after the firstlevel is full. The second energylevel can hold up to 8 electrons.

The second energylevel is the outermostlevel, so an oxygenatom has 6 valenceelectrons.

The third energy levelis the outermost level,so a sodium atom has1 valence electron.

c

The first energy level isclosest to the nucleus andcan hold up to 2 electrons.

The third energy level inthis model of a chlorineatom contains only 7electrons, for a total of 17electrons in the atom. Thisouter level of the atom isnot full.


Valence Electrons and the Periodic Table You can deter-mine the number of valence electrons in Figure 2 because youhave a model to look at. But what if you didn’t have a model?You have a tool that helps you determine the number of valenceelectrons for some elements—the periodic table!

Remember that elements in a group often have similarproperties, including the number of electrons in the outer-most energy level of their atoms. The number of valence elec-trons for many elements is related to the group number, asshown in Figure 3.

To Bond or Not to BondAtoms do not all bond in the same manner. In fact, someatoms rarely bond at all! The number of electrons in the outer-most energy level of an atom determines whether an atomwill form bonds.

Atoms of the noble, or inert, gases (Group 18) do not nor-mally form chemical bonds. As you just learned, atoms ofGroup 18 elements (except helium) have 8 valence electrons.Therefore, having 8 valence electrons must be a special con-dition. In fact, atoms that have 8 electrons in their outermostenergy level do not normally form new bonds. The outermostenergy level of an atom is considered to be full if it contains8 electrons.

Chapter 13330

Figure 3 Determining the Number of Valence Electrons

Atoms of elements in Groups 13–18have 10 fewer valence electrons thantheir group number. However, heliumatoms have only 2 valence electrons.

Atoms of elements in Groups 1and 2 have the same numberof valence electrons as theirgroup number.

Atoms of elements in Groups 3–12 donot have a general rule relating theirvalence electrons to their group number.

Determine the number ofvalence electrons in each ofthe following atoms: lithium(Li), beryllium (Be), aluminum(Al), carbon (C), nitrogen (N),sulfur (S), bromine (Br), andkrypton (Kr).


Atoms Bond to Have a Filled Outermost Level An atomthat has fewer than 8 valence electrons is more reactive, or morelikely to form bonds, than an atom with 8 valence electrons.Atoms bond by gaining, losing, or sharing electrons in order tohave a filled outermost energy level with 8 valence electrons.Figure 4 describes the ways in which atoms can achieve a filledoutermost energy level.

A Full Set—with Two? Not all atoms need 8 valence elec-trons for a filled outermost energy level. Helium atoms needonly 2 valence electrons. With only 2 electrons in the entireatom, the first energy level (which is also the outermost energylevel) is full. Atoms of hydrogen and lithium form bonds withother atoms in order to have 2 electrons.


Figure 4 These atomsachieve a full set of valenceelectrons in different ways.

1. What is a chemical bond?

2. What are valence electrons?

3. How many valence electrons does a silicon atom have?

4. Predict how atoms with 5 valence electrons will achievea full set of valence electrons.

5. Interpreting Graphics At right is a diagram of a fluorineatom. Will fluorine form bonds? Explain.

REVIEW

SulfurAn atom of sulfur has 6 valence electrons. It canhave 8 valence electrons by sharing 2 electronswith or gaining 2 electrons from other atoms tofill its outermost energy level.

MagnesiumAn atom of magnesium has 2 valence electrons. It can have a full outer level by losing 2 electrons.The second energy level becomes the outermostenergy level and contains a full set of 8 electrons.

Fluorine

NSTA

TOPIC: The Electron, The Periodic TableGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP305, HSTP310


332

Types of Chemical BondsAtoms bond by gaining, losing, or sharing electrons to havea filled outermost energy level containing eight valence elec-trons. The way in which atoms interact through their valenceelectrons determines the type of bond that forms. The threetypes of bonds are ionic (ie AHN ik), covalent (KOH VAY luhnt),and metallic.

Ionic BondsThe materials shown in Figure 5 have much in common.They are all hard, brittle solids at room temperature, theyall have high melting points, and they all contain ionicbonds. An ionic bond is the force of attraction betweenoppositely charged ions. Ions are charged particles that

form during chemical changes when one or morevalence electrons transfer from one atom to another.

A Transfer of Electrons An atomis neutral because the number ofelectrons equals the number of pro-tons. So their charges cancel eachother. A transfer of electrons betweenatoms changes the number of elec-trons in each atom, while the num-ber of protons stays the same. Thenegative charges and positive charges no longer cancel out, and the atoms become ions. Although an atom cannot gain (or lose) elec-trons without another atom nearbyto lose (or gain) electrons, it is easier to study the formation of ionsone at a time.

Atoms That Lose Electrons FormPositive Ions Ionic bonds formduring chemical changes whenatoms pull electrons away fromother atoms. The atoms that loseelectrons form ions that have fewerelectrons than protons. Because thepositive charges outnumber the neg-ative charges, these ions have anoverall positive charge.

Figure 5 Calcium carbonate in seashells, sodiumchloride in table salt, and calcium sulfate used tomake plaster of Paris casts all contain ionic bonds.

Section

2

ionic bond covalent bondions moleculecrystal lattice metallic bond

Describe ionic, covalent, andmetallic bonding.

Describe the propertiesassociated with substancescontaining each type of bond.


Metal Atoms Lose Electrons Atoms of most metals have fewelectrons in their outer energy level. When metal atoms bondwith other atoms, the metal atoms tend to lose these valenceelectrons and form positive ions. For example, look at the modelin Figure 6. An atom of sodium has one valence electron. Whena sodium atom loses this electron to another atom, it becomesa sodium ion. A sodium ion has a charge of 1+ because it con-tains 1 more proton than electrons. To show the differencebetween a sodium atom and a sodium ion, the chemical sym-bol for the ion is written as Na+. Notice that the charge is writ-ten to the upper right of the chemical symbol. Figure 6 alsoshows a model for the formation of an aluminum ion.

The Energy of Losing Electrons When an atom loses elec-trons, energy is needed to overcome the attraction betweenthe electrons and the protons in the atom’s nucleus. Removingelectrons from atoms of metals requires only a small amountof energy, so metal atoms lose electrons easily. In fact, theenergy needed to remove electrons from atoms of elements inGroups 1 and 2 is so low that these elements react very easily and can be found only as ions in nature. On the otherhand, removing electrons from atoms of nonmetals requires alarge amount of energy. Rather than give up electrons, theseatoms gain electrons when they form ionic bonds.


Figure 6 Forming Positive Ions

Sodium atom (Na)11+ protons11– electrons0 charge

Sodium ion (Na+)11+ protons10– electrons1+ charge

Aluminum atom (Al)13+ protons13– electrons0 charge

Aluminum ion (Al3+)13+ protons10– electrons3+ charge

Self-CheckLook at the periodictable, and determinewhich noble gas has thesame electron arrange-ment as a sodium ion.(See page 724 to checkyour answer.)

Here’s How It Works: During chemical changes, a sodium atom can lose its 1 electron in the thirdenergy level to another atom. The filled secondlevel becomes the outermost level, so the resultingsodium ion has 8 valence electrons.

Here’s How It Works: During chemical changes,an aluminum atom can lose its 3 electrons in thethird energy level to another atom. The filled sec-ond level becomes the outermost level, so theresulting aluminum ion has 8 valence electrons.


Atoms That Gain Electrons Form Negative Ions Atoms thatgain electrons from other atoms during chemical changes formions that have more electrons than protons. The negative chargesoutnumber the positive charges, giving each of these ions anoverall negative charge.

The outermost energy level of nonmetal atoms is almostfull. Only a few electrons are needed to fill the outer level, soatoms of nonmetals tend to gain electrons from other atoms.For example, look at the model in Figure 7. An atom of chlo-rine has 7 valence electrons. When a chlorine atom gains 1electron to complete its outer level, it becomes an ion with a1– charge called a chloride ion. The symbol for the chloride ionis Cl–. Notice that the name of the negative ion formed fromchlorine has the ending -ide. This ending is used for the namesof the negative ions formed when atoms gain electrons. Figure7 also shows a model of how an oxide ion is formed.

The Energy of Gaining Electrons Atoms of most nonmetalsfill their outermost energy level by gaining electrons. Energyis given off by most nonmetal atoms during this process. Themore easily an atom gains an electron, the more energy anatom gives off. Atoms of the Group 17 elements (the halogens)give off the most energy when they gain an electron. The halo-gens, such as fluorine and chlorine, are extremely reactive non-metals because they release a large amount of energy.

Chapter 13334

Figure 7 Forming Negative Ions

Charge!Calculating the charge of anion is the same as addingintegers (positive or negativewhole numbers or zero) withopposite signs. You write thenumber of protons as a posi-tive integer and the number of electrons as a negative inte-ger and then add the integers.Calculate the charge of an ionthat contains 16 protons and18 electrons. Write the ion’ssymbol and name.

MATH BREAK

Oxygen atom (O)8+ protons8– electrons0 charge

Oxide ion (O2–)8+ protons

10– electrons2– charge

Chlorine atom (Cl)17+ protons17– electrons0 charge

Chloride ion (Cl–)17+ protons18– electrons1– charge

Here’s How It Works: During chemical changes, a chlorine atom gains 1 electron in the third en-ergy level from another atom. A chloride ion isformed with 8 valence electrons. Thus, its outer-most energy level is filled.

Here’s How It Works: During chemical changes,an oxygen atom gains 2 electrons in the secondenergy level from another atom. An oxide ion isformed with 8 valence electrons. Thus, its outer-most energy level is filled.


Charged Ions Form a Neutral Compound When a metalreacts with a nonmetal, the same number of electrons is lostby the metal atoms as is gained by the nonmetal atoms. Eventhough the ions that bond are charged, the compound formedis neutral because the charges of the ions cancel each otherthrough ionic bonding. An ionic bond is an example of electrostatic attraction in which opposite electric charges stick together. Another example is static cling, illustrated in Figure 8.

Ions Bond to Form a Crystal Lattice The ions that make upan ionic compound are bonded in a repeating three-dimensionalpattern called a crystal lattice (KRI stuhl LAT is). In ionic com-pounds, such as table salt, the ions in the crystal lattice arearranged as alternating positive and negative ions, forming asolid. The model in Figure 9 shows a small part of a crystal lat-tice. The arrangement of bonded ions in a crystal lattice deter-mines the shape of the crystals of an ionic compound.

The strong force of attraction between bonded ions in acrystal lattice gives ionic compounds certain properties, includ-ing a high melting point and boiling point. Ionic compoundstend to be brittle solids at room temperature and usually breakapart when hit with a hammer.


Figure 8 Like ionic bonds, staticcling is the result of the attrac-tion between opposite charges.

1. How does an atom become a negative ion?

2. What are two properties of ionic compounds?

3. Applying Concepts Which group of elements lose 2valence electrons when their atoms form ionic bonds?What charge would the ions formed have?

REVIEW

Figure 9 This model of the crystal lattice of sodium chloride,

or table salt, shows a three-dimensional view

of the bonded ions.


Covalent BondsMost materials you encounter every day, such as water,sugar, and carbon dioxide, are held together by bondsthat do not involve ions. These substances tend to havelow melting and boiling points, and some of these sub-stances are brittle in the solid state. The type of bondsfound in these substances, including the substancesshown in Figure 10, are covalent bonds.

A covalent bond is the force of attraction betweenthe nuclei of atoms and the electrons shared by theatoms. When two atoms of nonmetals bond, a largeamount of energy is required for either atom to lose anelectron, so no ions are formed. Rather than transferringelectrons to complete their outermost energy levels, twononmetal atoms bond by sharing electrons with oneanother, as shown in the model in Figure 11.

Covalently Bonded Atoms Make Up Molecules The parti-cles of substances containing covalent bonds differ from thosecontaining ionic bonds. Ionic compounds consist of ions organ-ized in a crystal. Covalent compounds consist of individualparticles called molecules (MAHL i KYOOLZ). A molecule is aneutral group of atoms held together by covalent bonds. InFigure 11, you saw a model of a hydrogen molecule, which iscomposed of two hydrogen atoms covalently bonded. However,most molecules are composed of atoms of two or more el-ements. The models in Figure 12 show two ways to representthe covalent bonds in a molecule.

Chapter 13336

Figure 10 Covalentbonds are found in this plastic ball, the paddle’srubber covering, the cotton fibers in clothes,and even many of thesubstances that make up the human body!

Figure 11 By sharing electrons in a covalentbond, each hydrogen atom (the smallestatom known) has a full outermost energylevel containing two electrons.

Make models of molecules outof marshmallows on page 680

of the LabBook.

The shared electrons spend most of theirtime between the nuclei of the atoms.

The protons and the shared electrons attractone another. This attraction is the basis of thecovalent bond that holds the atoms together.


Making Electron-Dot Diagrams

An electron-dot diagram is a model that showsonly the valence electrons in an atom. Electron-dotdiagrams are helpful when predicting how atomsmight bond. You draw an electron-dot diagram bywriting the symbol of the element and placing the

correct number of dots around it. This type ofmodel can help you to better understand bondingby showing the number of valence electrons andhow atoms share electrons to fill their outermostenergy levels, as shown below.


Figure 12 Covalent Bonds in a Water Molecule

••••

••••O HH

Another way to showcovalent bonds is to draw an electron-dot diagram.An electron-dot diagramshows only the outermostlevel of electrons for eachatom. But you can still seehow electrons are sharedbetween the atoms.

Each hydrogen atom shares its 1electron with the oxygen atom. Thisallows each hydrogen to have afilled outer level with 2 electrons.

Through covalent bonding,the oxygen atom sharesone of its electrons witheach of the two hydrogenatoms. As a result, it has a filled outermost energylevel with 8 electrons.

Self-Check1. How many dots does the electron-dot diagram of

a sulfur atom have?

2. How is a covalent bond different from an ionicbond? (See page 724 to check your answers.)

Carbon atoms have 4valence electrons, so 4dots are placed aroundthe symbol. A carbonatom needs 4 moreelectrons for a filledoutermost energy level.

Oxygen atoms have 6valence electrons, so 6dots are placed aroundthe symbol. An oxygenatom needs only 2 moreelectrons for a filled outermost energy level.

The noble gas kryptonhas a full set of 8valence electrons in itsatoms. Thus, krypton isnonreactive because itsatoms do not need anymore electrons.

This electron-dot dia-gram represents hydro-gen gas, the samesubstance shown in themodel in Figure 11.

C•••

•

•••• ••O

••

•••• ••Kr ••H H


A Molecule Is the Smallest Particle of a CovalentCompound An atom is the smallest particle intowhich an element can be divided and still be thesame substance. Likewise, a molecule is the small-est particle into which a covalently bonded com-

pound can be divided and still be thesame compound. Figure 13 illustrates

how a sample of water is made upof many individual molecules

of water (shown as three-dimensional models). If youcould divide water over andover, you would eventuallyend up with a single mol-ecule of water. However, ifyou separated the hydrogenand oxygen atoms that makeup a water molecule, youwould no longer have water.

The Simplest Molecules All molecules are composed of atleast two covalently bonded atoms. The simplest molecules,known as diatomic molecules, consist of two atoms bondedtogether. Some elements are called diatomic elements becausethey are found in nature as diatomic molecules composed oftwo atoms of the element. Hydrogen is a diatomic element,as you saw in Figure 11. Oxygen, nitrogen, and the halogensfluorine, chlorine, bromine, and iodine are also diatomic. Bysharing electrons, both atoms of a diatomic molecule can filltheir outer energy level, as shown in Figure 14.

Chapter 13338

Figure 14 Models of a Diatomic Fluorine Molecule

This is a three-dimensionalmodel of a fluorine molecule.

Figure 13 The water in this fishbowl is made up of many tiny water molecules.Each molecule is the smallestparticle that still has thechemical properties of water.

Two covalently bonded fluorine atoms have filledoutermost energy levels.The pair of electronsshared by the atoms arecounted as valence elec-trons for each atom.

Try your hand at drawingelectron-dot diagrams for a molecule of chlorine (adiatomic molecule) and amolecule of ammonia (onenitrogen atom bonded withthree hydrogen atoms).


More-Complex Molecules Diatomic molecules are the sim-plest—and some of the most important—of all molecules. Youcould not live without diatomic oxygen molecules. But otherimportant molecules are much more complex. Gasoline, plas-tic, and even proteins in the cells of your body are examplesof complex molecules. Carbon atoms are the basis of many ofthese complex molecules. Each carbon atom needs to make 4covalent bonds to have 8 valence electrons. These bonds canbe with atoms of other elements or with other carbon atoms,as shown in the model in Figure 15.

Metallic BondsLook at the unusual metal sculp-ture shown in Figure 16. Notice thatsome metal pieces have been flat-tened, while other metal pieceshave been shaped into wires. Howcould the artist change the shapeof the metal into all of these dif-ferent forms without breaking themetal into pieces? A metal can beshaped because of the presence ofa special type of bond called ametallic bond. A metallic bond isthe force of attraction between a positively charged metal ion and the electrons in a metal.(Remember that metal atoms tendto lose electrons and form posi-tively charged ions.)

339Chemical Bonding

Figure 16 The different shapes of metalin this sculpture are possible because ofthe bonds that hold the metal together.

Figure 15 A granola bar contains sucrose, or table sugar. A mol-ecule of sucrose is composed of carbon atoms, hydrogen atoms, and oxygen atoms joined by covalent bonds.


Proteins perform many functionsthroughout your body, such as digest-ing your food, building componentsof your cells, and transporting nutri-ents to each cell. A single protein canhave a chain of 7,000 atoms of car-bon and nitrogen with atoms of otherelements covalently bonded to it.

Hydrogen

Carbon

Oxygen


Bending with Bonds

1. Straighten out a wirepaper clip. Recordthe result in yourScienceLog.

2. Bend a piece of chalk.Record the result in yourScienceLog.

3. Chalk is composed of cal-cium carbonate, a com-pound containing ionicbonds. What type of bondsare present in the paperclip?

4. In your ScienceLog, explainwhy you could change theshape of the paper clip butcould not bend the chalkwithout breaking it.

Chapter 13340

Gold can be pounded out tomake a foil only a few atomsthick. A piece of gold thesize of the head of a pin canbe beaten into a thin “leaf”that would cover this page!

Electrons Move Throughout a Metal The scientific under-standing of the bonding in metals is that the metal atoms getso close to one another that their outermost energy levels over-lap. This allows their valence electrons to move throughout themetal from the energy level of one atom to the energy levelsof the atoms nearby. The atoms form a crystal much like theions associated with ionic bonding. However, the negativecharges (electrons) in the metal are free to move about. You canthink of a metal as being made up of positive metal ions withenough valence electrons “swimming” about to keep the ionstogether and to cancel the positive charge of the ions, as shownin Figure 17. The ions are held together because metallic bondsextend throughout the metal in all directions.

Metals Conduct Electric Current Metallic bonding is thereason why metals have particular properties. One of theseproperties is electrical conductivity—the ability to conduct elec-tric current. For example, when you turn on a lamp, electronsmove within the copper wire that connects the lamp with theoutlet. The electrons that move are the valence electrons inthe copper atoms. These electrons are free to move because ofmetallic bonds—they are not connected to any one atom.

Metals Can Be Reshaped Metallic bonds allow atoms inmetals to be rearranged. As a result, metals can be reshaped.The properties of ductility (the ability to be drawn into wires)and malleability (the ability to be hammered into sheets)describe a metal’s ability to be reshaped. For example, copperis made into wires for use in electrical cords. Aluminum canbe pounded into thin sheets and made into aluminum foiland cans.

Figure 17 The moving electrons are attracted to the metal ions, forming metallic bonds.

The positive metal ions are infixed positions in the metal.

Negative electrons arefree to move about.


•••C•• •H •

HH

How Metals Can Bend Without Breaking When a pieceof metal is bent, some of the metal ions are forced closertogether. You might expect the metal to break because thepositive ions repel one another. However, even in their newpositions, the positive ions are surrounded by and attracted tothe electrons, as shown in Figure 18. (Ionic compounds dobreak when hit because neither the positive ions nor the nega-tive ions are free to move.)

Figure 18 The shape of a metal can bechanged without breaking because metallicbonds occur in many directions.

The moving electrons maintainthe metallic bonds no matter howthe shape of the metal changes.

The repulsion between the positivelycharged metal ions increases as theions are pushed closer to one another.


1. What happens to electrons in covalent bonding?

2. What type of element is most likely to form covalent bonds?

3. What is a metallic bond?

4. Interpreting Graphics Thiselectron-dot diagram is not yetcomplete. Which atom needsto form another covalentbond? How do you know?

REVIEW

Metallic Bonding in StaplesAlthough they are not very glamorous, metal staples are veryuseful in holding things such as sheets of paper together.Explain how the metallic bonds in a staple allow it tochange shape so that it can function properly.

NSTA

TOPIC: Types of Chemical Bonds, Properties of Metals



Chapter Highlights

Chapter 13342

SECTION 1 SECTION 2

Vocabularychemical bonding (p. 328)

chemical bond (p. 328)

valence electrons (p. 329)

Section Notes

• Chemical bonding is thejoining of atoms to form newsubstances. A chemical bondis a force of attraction thatholds two atoms together.

• Valence electrons are theelectrons in the outermostenergy level of an atom.These electrons are used toform bonds.

• Most atoms form bonds bygaining, losing, or sharingelectrons until they have 8valence electrons. Atoms ofhydrogen, lithium, and he-lium need only 2 electrons tofill their outermost level.

Vocabularyionic bond (p. 332)

ions (p. 332)

crystal lattice (p. 335)

covalent bond (p. 336)

molecule (p. 336)

metallic bond (p. 339)

Section Notes

• In ionic bonding, electronsare transferred between twoatoms. The atom that loseselectrons becomes a positiveion. The atom that gainselectrons becomes a negativeion. The force of attractionbetween these oppositelycharged ions is an ionicbond.

• Ionic bonding usually occursbetween atoms of metals andatoms of nonmetals.

Skills CheckVisual UnderstandingDETERMINING VALENCE ELECTRONSKnowing the number of valence electrons in anatom is important in predicting how it will bondwith other atoms. Review Figure 3 onpage 330 to learn how an element’slocation on the periodic tablehelps you determine the numberof valence electrons in an atom.

FORMING IONS Turn back toFigures 6 and 7 on pages 333–334to review how ions are formedwhen atoms lose or gain electrons.

Math ConceptsCALCULATING CHARGE To calculate the charge of an ion, you must add integers withopposite signs. The total positive charge of theion (the number of protons) is written as apositive integer. The total negative charge ofthe ion (the number of electrons) is written as a negative integer. For example, the charge ofan ion containing 11 protons and 10 electronswould be calculated as follows:

(11) (10) 1



TOPIC: The Electron sciLINKS NUMBER: HSTP305

TOPIC: The Periodic Table sciLINKS NUMBER: HSTP310

TOPIC: Types of Chemical Bonds sciLINKS NUMBER: HSTP315

TOPIC: Properties of Metals sciLINKS NUMBER: HSTP320



KEYWORD: HSTBND

343Chemical Bonding

SECTION 2

• Energy is needed to removeelectrons from metal atomsto form positive ions. Energyis released when most non-metal atoms gain electrons to form negative ions.

• In covalent bonding, elec-trons are shared by twoatoms. The force of attractionbetween the nuclei of theatoms and the shared elec-trons is a covalent bond.

• Covalent bonding usuallyoccurs between atoms ofnonmetals.

• Electron-dot diagrams are asimple way to represent thevalence electrons in an atom.

• Covalently bonded atomsform a particle called a mol-ecule. A molecule is thesmallest particle of a com-pound with the chemicalproperties of the compound.

• Diatomic elements are theonly elements found innature as diatomic moleculesconsisting of two atoms ofthe same element covalentlybonded together.

• In metallic bonding, theoutermost energy levels ofmetal atoms overlap, allow-ing the valence electrons tomove throughout the metal.The force of attractionbetween a positive metal ion and the electrons in themetal is a metallic bond.

• Many properties of metals,such as conductivity, duc-tility, and malleability, resultfrom the freely moving elec-trons in the metal.

LabsCovalent Marshmallows (p. 680)



To complete the following sentences, choosethe correct term from each pair of terms listedbelow.

1. The force of attraction that holds twoatoms together is a ____. (crystal lattice orchemical bond)

2. Charged particles that form when atomstransfer electrons are ____. (molecules or ions)

3. The force of attraction between the nucleiof atoms and shared electrons is a(n) ____.(ionic bond or covalent bond)

4. Electrons free to move throughout amaterial are associated with a(n) ____.(ionic bond or metallic bond)

5. Shared electrons are associated with a____. (covalent bond or metallic bond)


Multiple Choice

6. Which element has a full outermostenergy level containing only twoelectrons?a. oxygen (O) c. fluorine (F)b. hydrogen (H) d.helium (He)

7. Which of the following describes whathappens when an atom becomes an ionwith a 2– charge?a. The atom gains 2 protons.b. The atom loses 2

protons.c. The atom gains

2 electrons.d.The atom loses

2 electrons.

Chapter 13344

8. The propertiesof ductility andmalleability areassociated with which type of bonds?a. ionicb. covalentc. metallicd.none of the above

9. In which area of the periodic table do youfind elements whose atoms easily gainelectrons?a. across the top two rowsb. across the bottom rowc. on the right sided.on the left side

10. What type of element tends to lose elec-trons when it forms bonds?a. metalb. metalloidc. nonmetald.noble gas

11. Which pair of atoms can form an ionicbond?a. sodium (Na) and potassium (K)b. potassium (K) and fluorine (F)c. fluorine (F) and chlorine (Cl) d. sodium (Na) and neon (Ne)

Short Answer

12. List two properties of covalent compounds.

13. Explain why an iron ion is attracted to asulfide ion but not to a zinc ion.

14. Using your knowledge of valence elec-trons, explain the main reason so manydifferent molecules are made from carbonatoms.

15. Compare the three types of bonds basedon what happens to the valence electronsof the atoms.


Concept Mapping

16. Use the followingterms to create aconcept map:chemical bonds, ionic bonds, covalentbonds, metallic bonds,molecule, ions.


17. Predict the type of bond each of the fol-lowing pairs of atoms would form:a. zinc (Zn) and zinc (Zn)b. oxygen (O) and nitrogen (N)c. phosphorus (P) and oxygen (O)d.magnesium (Mg) and chlorine (Cl)

18. Draw electron-dot diagrams for each ofthe following atoms, and state how manybonds it will have to make to fill its outerenergy level.a. sulfur (S)b. nitrogen (N)c. neon (Ne)d. iodine (I)e. silicon (Si)

19. Does the substance being hit in the photobelow contain ionic or metallic bonds?Explain.

MATH IN SCIENCE

20. For each atom below, write the number ofelectrons it must gain or lose to have 8valence electrons. Then calculate thecharge of the ion that would form.a. calcium (Ca) c. bromine (Br)b. phosphorus (P) d. sulfur (S)


Look at the picture of the wooden pencilbelow, and answer the following questions.

21. In which part of the pencil are metallicbonds found?

22. List three materials composed of mol-ecules with covalent bonds.

23. Identify two differences between theproperties of the metallically bondedmaterial and one of the covalentlybonded materials.




ReadingCheck-up



Left-Handed Molecules

346

Some researchers think that light from a newlyforming star 1,500 light-years away (1 light-year is equal to about 9.6 trillion kilometers)may hold the answer to an Earthly riddle thathas been puzzling scientists for over 100 years!

We Are All Lefties!In 1848, Louis Pasteur discovered that carbon-containing molecules come in left-handed andright-handed forms. Each of the molecules isan exact mirror image of the other, just aseach of your hands is a mirror image of theother. These molecules are made of the sameelements, but they differ in the elements’arrangement in space.

Shortly after Pasteur’s discovery,researchers stumbled across an interesting but unexplained phenomenon—all organisms,including humans, are made almost entirely of left-handed molecules! Chemists werepuzzled by this observation because whenthey made amino acids in the laboratory, theamino acids came out in equal numbers ofright- and left-handed forms. Scientists also

found that organisms cannot even use theright-handed form of the amino acids to make proteins! For years, scientists have triedto explain this. Why are biological moleculesusually left-handed and not right-handed?

Cosmic ExplanationAstronomers recently discovered that a newlyforming star in the constellation Orion emits aunique type of infrared light. Infrared light hasa wavelength longer than the wavelenth of vis-ible light. The wave particles of this light spiralthrough space like a corkscrew. This light spi-rals in only one direction. Researchers suspectthat this light might give clues to why allorganisms are lefties.

Laboratory experiments show that depend-ing on the direction of the ultraviolet lightspirals, either left-handed or right-handedmolecules are destroyed. Scientists wonder if a similar type of light may have been presentwhen life was beginning on Earth. Such lightmay have destroyed most right-handed mol-ecules, which explains why life’s molecules are left-handed.

Skeptics argue that the infrared light hasless energy than the ultraviolet light used in the laboratory experiments and thus is not avalid comparison. Some researchers, however,hypothesize that both infrared and ultravioletlight may be emitted from the newly formingstar that is 1,500 light-years away.

Find Out More The French chemist Pasteur discovered left-handed and right-handed molecules in tartaricacid. Do some research to find out more aboutPasteur and his discovery. Share your findingswith the class.

Molecules, such as the carbon moleculesshown above, often come in two mirror-image forms, just as hands do.


347

Here’s Looking At Ya’!

To some people, just the thought of puttingsmall pieces of plastic in their eyes isuncomfortable. But for millions of others,

those little pieces of plastic, known as contactlenses, are a part of daily life. So what would youthink about putting a piece of glass in your eyeinstead? Strangely enough, the humble beginningof the contact lens began with doing just that—inserting a glass lens right in the eye! Ouch!

Molded GlassEarly developers of contactlenses had only glass touse until plastics were dis-covered. In 1929, aHungarian physiciannamed Joseph Dalloscame up with a way tomake a mold of thehuman eye. This was acritical step in the devel-opment of contact lenses.He used these molds tomake a glass lens that fol-lowed the shape of theeye rather than laying flatagainst it. In combinationwith the eye’s natural lens,light was refocused toimprove a person’s eye-sight. As you can probablyguess, glass lenses weren’tvery comfortable.

Still Too Hard Seven years later, an American optometrist,William Feinbloom, introduced contact lensesmade of hard plastic. Plastic was a newly devel-oped material made from long, stable chains ofcarbon, hydrogen, and oxygen molecules calledpolymers. But polymers required a lot of work to make. Chemists heated short chains, forcing

them to chemically bond to form a longer, more-stable polymer. The whole process was alsoexpensive. To make matters worse, the hard-plastic lenses made from polymers weren’t muchmore comfortable than the glass lenses.

How About Spinning Plastic Gel?In an effort to solve the comfort problem,Czech chemists Otto Wichterle and DrahoslavLim invented a water-absorbing plastic gel. Thelenses made from this gel were soft and pli-

able, and they allowed airto pass through the lensto the eye. These charac-teristics made the lensesmuch more comfortableto wear than the glasslenses.

Wichterle solved thecost problem by develop-ing a simple and inexpen-sive process to make theplastic-gel lenses. In thisprocess, called spin cast-ing, liquid plastic is addedto a spinning mold of aneye. When the plasticforms the correct shape, itis treated with ultravioletand infrared light, whichhardens the plastic. Bothplastic gel and spin cast-ing were patented in

1963, becoming the foundation for the contactlenses people wear today.

Look Toward the Future What do you think contact lenses might belike in 20 years? Let your imagination run wild.Sometimes the strangest ideas are the bestseeds of new inventions!

Does the thought of puttingsomething in your eye makeyou squirm?


348 Chapter 14

Forming New Substances . . . . . . . . . 350

MathBreak . . . . . . . . . 352MathBreak . . . . . . . . . 356QuickLab . . . . . . . . . . 357Internet Connect . . . . 357

Types of ChemicalReactions . . . . . . . . . . . 358


Energy and Rates ofChemical Reactions . . 361

Biology Connection . . 362Apply . . . . . . . . . . . . . 363QuickLab . . . . . . . . . . 364QuickLab . . . . . . . . . . 365Internet Connect . . . . 365

Chapter Review . . . . . . . . . . 368

Feature Article . . . . . . . 370, 371

LabBook . . . . . . . . . . . . 682–687

ChemicalReactionsChemicalReactions


1. What clues can help you identify a chemicalreaction?

2. What are some types ofchemical reactions?

3. How can you change therate of a chemical reaction?


Chemical Reactions 349

A MODEL FORMULAChemicals react in very precise ways.In this activity, you will model achemical reaction and predict howchemicals react.

Procedure

1. You will receive severalmodels that are made from marshmallows stuck togetherwith toothpicks. Each of thesemodels is a Model A.

2. Your teacher will show you ModelB and Model C. Take apart one ormore Model A’s to make copies ofmodel B and Model C.

3. Do you have any pieces left over?If so, use them to make moreModel B’s and/or Model C’s. Doyou need more parts to completeModel B or Model C? If so, takeapart another Model A.

4. If necessary, repeat step 3 untilyou have no parts left over.

Analysis

5. How many Model A’s did you useto make copies of Model B andModel C?

6. How many Model B’s did youmake? How many Model C’s didyou make?

7. Suppose you needed to make sixModel B’s. How many Model A’swould you need? How manyModel C’s could you make withthe leftover parts?

Reaction to the RescueA car slams into a wall at 97 km/h (60 mph) during a crashtest. Although both dummies are wearing seat belts, onesuffers a crushing blow to the head as it strikes the dash-board. The other suffers only minor bruises thanks to an airbag. Air bags can inflate rapidly due to a chemical reactionthat produces gas at a very fast rate. In this chapter youwill learn how to identify and describe a chemical reaction.You will also learn about factors that affect the rate of areaction.

Reaction to the RescueA car slams into a wall at 97 km/h (60 mi/h) during a crash test. Although both dummies arewearing seat belts, one suffers a crushing blow tothe head as it strikes the dashboard. The other suffers only minor bruises, thanks to an air bag. Air bags can inflate rapidly because of a chemicalreaction that produces gas at a very fast rate. Inthis chapter, you will learn how to identify anddescribe a chemical reaction. You will also learnabout factors that affect the rate of a reaction.


Chapter 14350

Forming New SubstancesEach fall, an amazing transformation takes place. Leaves change

color, as shown in Figure 1. Vibrant reds, oranges,and yellows that had been hidden by green all year

are seen as the temperatures get cooler and thehours of sunlight become fewer. What is hap-

pening to cause this change? Leaves have agreen color as a result of a compound called

chlorophyll (KLOR uh FIL). Each fall, the chloro-phyll undergoes a chemical change and forms sim-pler substances that have no color. You can see thered, orange, and yellow colors in the leaves because

the green color of the chlorophyll no longer hides them.

Chemical Reactions The chemical change that occurs as chlorophyll breaks downinto simpler substances is one example of a chemical reaction.A chemical reaction is the process by which one or more sub-stances undergo change to produce one or more different sub-stances. These new substances have different chemical andphysical properties from the original substances. Many of thechanges you are familiar with are chemical reactions, includ-ing the ones shown in Figure 2.

Figure 1 The change of color in thefall is a result of chemical changesin the leaves.

Figure 2 Examples of Chemical Reactions

The substances that make up baking powder undergo a chemical reaction when mixed with water. One newsubstance that forms is carbon dioxide gas, which causesthe bubbles in this muffin.

Once ignited, gasoline reacts with oxygen gas inthe air. The new substances that form, carbondioxide and water, push against the pistons inthe engine to keep the car moving.

Section

1

chemical reactionchemical formulachemical equationreactantsproductslaw of conservation of mass

Identify the clues that indicate a chemical reactionmight be taking place.

Interpret and write simplechemical formulas.

Interpret and write simplebalanced chemical equations.

Explain how a balancedequation illustrates the law ofconservation of mass.



Clues to Chemical Reactions How can you tell when achemical reaction is taking place? There are several clues thatindicate when a reaction might be occurring. The more ofthese clues you observe, the more likely it is that the changeis a chemical reaction. Several of these clues are described below.


Some Clues to Chemical Reactions

Gas FormationThe formation of gas bubbles is a clue that a chemicalreaction might be taking place. For example, bubbles ofcarbon dioxide are produced when hydrochloric acid isplaced on a piece of limestone.

Solid FormationA solid formed in a solutionas a result of a chemicalreaction is called a precipitate(pruh SIP uh TAYT). Here yousee potassium chromate solu-tion being added to a silvernitrate solution. The dark redsolid is a precipitate of silverchromate.

Color ChangeChlorine bleach is great for removingthe color from stains on white clothes.But don’t spill it on your jeans. Thebleach reacts with the blue dye on thefabric, causing the color of the materialto change.

Energy ChangeEnergy is released during some chemicalreactions. A fire heats a room and provideslight. Electrical energy is released whenchemicals in a battery react. During someother chemical reactions, energy is absorbed.Chemicals on photographic film react whenthey absorb energy from light shining on the film.


Breaking and Making Bonds New substances are formedin a chemical reaction because chemical bonds in the startingsubstances break, atoms rearrange, and new bonds form tomake the new substances. Look at the model in Figure 3 tounderstand how this process occurs.

Chemical FormulasRemember that a chemical symbol is a shorthand method ofidentifying an element. A chemical formula is a shorthandnotation for a compound or a diatomic element using chemi-cal symbols and numbers. A chemical formula indicates thechemical makeup by showing how many of each kind of atomis present in a molecule.

The chemical formula for water, H2O, tells you that a watermolecule is composed of two atoms of hydrogen and one atomof oxygen. The small number 2 in the formula is a subscript.A subscript is a number written below and to the right of achemical symbol in a formula. When no subscript is writtenafter a symbol, as with the oxygen in water’s formula, onlyone atom of that element is present. Figure 4 shows two morechemical formulas and what they mean.

Chapter 14352

Figure 3Reaction of Hydrogen and Chlorine

Breaking Bonds The elements hydrogen and chlo-rine are diatomic, meaning they are composed ofmolecules that consist of two atoms bondedtogether. For these molecules to react, the bondsjoining the atoms must break.

Making Bonds Molecules of the new substance,hydrogen chloride, are formed as new bonds aremade between hydrogen atoms and chlorineatoms.

Figure 4 A chemical formula shows the number of atoms of each element present.

Oxygen is a diatomic element.Each molecule of oxygen gas is composed of two atoms ofoxygen bonded together.

Counting AtomsSome chemical formulascontain two or more chemi-cal symbols enclosed byparentheses. When countingatoms in these formulas,multiply everything inside theparentheses by the subscriptas though they were part of amathematical equation. Forexample, Ca(NO3)2 contains:

1 calcium atom 2 nitrogen atoms (2 1)6 oxygen atoms (2 3)

Now It’s Your TurnDetermine the number ofatoms of each element in theformulas Mg(OH)2 andAl2(SO4)3.

MATH BREAK

O2Every molecule of glucose (thesugar formed by plants duringphotosynthesis) is composedof six atoms of carbon, twelveatoms of hydrogen, and sixatoms of oxygen.

C6H12O6


Writing Formulas for Covalent Compounds You can oftenwrite a chemical formula if you know the name of the sub-stance. Remember that covalent compounds are usuallycomposed of two nonmetals. The names of covalent com-pounds use prefixes to tell you how many atoms of eachelement are in the formula. A prefix is a syllable or sylla-bles joined to the beginning of a word. Each prefix used ina chemical name represents a number, as shown in the tableat right. Figure 5 demonstrates how to write a chemical for-mula from the name of a covalent compound.

Writing Formulas for IonicCompounds If the name of acompound contains the name ofa metal and a nonmetal, thecompound is probably ionic. Towrite the formula for an ioniccompound, you must make surethe compound’s overall charge iszero. In other words, the formulamust have subscripts that causethe charges of the ions to cancelout. (Remember that the chargeof many ions can be determinedby looking at the periodic table.)Figure 6 demonstrates how towrite a chemical formula fromthe name of an ionic compound.


Self-CheckHow many atoms of each element make up Na2SO4?(See page 724 to check your answer.)

Prefixes Used in Chemical Names

mono- 1 hexa- 6

di- 2 hepta- 7

tri- 3 octa- 8

tetra- 4 nona- 9

penta- 5 deca- 10

Figure 5 The formulas ofthese covalent compoundscan be written using theprefixes in their names.

Carbon dioxide Dinitrogen monoxide

CO2 N2OThe lack of a prefixindicates 1 carbon atom.The prefix di- indicates2 oxygen atoms.

The prefix di- indicates 2 nitrogen atoms. The prefix mono- indicates1 oxygen atom.

Sodium chloride Magnesium chloride

NaCl MgCl2A magnesium ion has a 2 charge.A chloride ion has a 1 charge.

A sodium ion has a 1 charge.A chloride ion has a 1 charge.

One sodium ion and onechloride ion have an overallcharge of (1) (1) = 0

One magnesium ion and twochloride ions have an overall charge of (2) 2(1) = 0

Figure 6 The formula of an ionic compound is written byusing enough of each ion so the overall charge is zero.


Chemical EquationsA composer writing a piece of music, like the one inFigure 7, must communicate to the musician whatnotes to play, how long to play each note, and inwhat style each note should be played. The composerdoes not use words to describe what must happen.Instead, he or she uses musical symbols to commu-nicate in a way that can be easily understood by any-one in the world who can read music.

Similarly, people who work with chemical reac-tions need to communicate information about reac-tions clearly to other people throughout the world.Describing reactions using long descriptive sentenceswould require translations into other languages.Chemists have developed a method of describing reac-tions that is short and easily understood by anyonein the world who understands chemical formulas. Achemical equation is a shorthand description of achemical reaction using chemical formulas and sym-bols. Because each element’s chemical symbol isunderstood around the world, a chemical equationneeds no translation.

Reactants Yield Products Consider theexample of carbon reacting with oxygen toyield carbon dioxide, as shown in Figure 8.The starting materials in a chemical reac-tion are reactants (ree AKT UHNTS). The sub-stances formed from a reaction are products.In this example, carbon and oxygen are reac-tants, and carbon dioxide is the productformed. The parts of the chemical equationfor this reaction are described in Figure 9.

Figure 8 Charcoal is used tocook food on a barbecue. Whencarbon in charcoal reacts withoxygen in the air, the primaryproduct is carbon dioxide.

Chapter 14354

Figure 9 The Parts of a Chemical Equation

A plus sign separates the for-mulas of two or more reactantsor products from one another.

C+O2 CO2

The arrow, also called the yieldssign, separates the formulas ofthe reactants from the formulasof the products.

The formulas of the reactantsare written before the arrow.

The formulas of the productsare written after the arrow.

Figure 7 The symbols on this music areunderstood around the world—just likechemical symbols!


Accuracy Is Important The symbol or formula for each substance in the reaction must be written correctly. For acompound, determine if it is covalent or ionic, and write theappropriate formula. For an element, use the proper chemicalsymbol, and be sure to use a subscript of 2 for the diatomicelements. (The seven diatomic elements are hydrogen, nitro-gen, oxygen, fluorine, chlorine, bromine, and iodine.) Anequation with an incorrect chemical symbol or formula willnot accurately describe the reaction. In fact, even a simplemistake can make a huge difference, as shown in Figure 10.

An Equation Must Be Balanced In a chemical reaction,every atom in the reactants becomes part of the products.Atoms are never lost or gained in a chemical reaction. Whenwriting a chemical equation, you must show that the numberof atoms of each element in the reactants equals the numberof atoms of those elements in the products by writing abalanced equation.


Self-CheckWhen calcium bromide reacts with chlorine,bromine and calcium chloride are produced. Writean equation to describe this reaction. Identify eachsubstance as either a reactant or a product. (See page 724 to check your answers.)

Hydrogen gas, H2, is animportant fuel that may help reduce air pollution.Because water is the onlyproduct formed as hydro-gen burns, there is little airpollution from vehicles thatuse hydrogen as fuel.

The chemical symbol for theelement cobalt is Co. Cobalt is ahard, bluish gray metal.

The chemical formula for thecompound carbon monoxide isCO. Carbon monoxide is a col-orless, odorless, poisonous gas.

The chemical formula for thecompound carbon dioxide is CO2.Carbon dioxide is a colorless,odorless gas that you exhale.

Figure 10 The symbols and formulasshown here are similar, but don’t confuse them while writing an equation!


H2 + O2 H2O

Reactants Products

How to Balance an Equation Writing a balanced equationrequires the use of coefficients (KOH uh FISH uhnts). A coefficientis a number placed in front of a chemical symbol or formula.When counting atoms, you multiply a coefficient by the sub-script of each of the elements in the formula that follows it.Thus, 2CO2 represents 2 carbon dioxide molecules. Together thetwo molecules contain a total of 2 carbon atoms and 4 oxygenatoms. Coefficients are used when balancing equations becausethe subscripts in the formulas cannot be changed. Changing asubscript changes the formula so that it no longer representsthe correct substance. Study Figure 11 to see how to use coef-ficients to balance an equation. Then you can practice balanc-ing equations by doing the MathBreak at left.

Chapter 14356

Figure 11 Follow these steps to write abalanced equation for H2 + O2 H2O.

Count the atoms ofeach element in thereactants and in theproducts. You can seethat there are feweroxygen atoms in theproducts than in thereactants.

1

Balancing ActWhen balancing a chemicalequation, you must placecoefficients in front of anentire chemical formula,never in the middle of a for-mula. Notice where the coef-ficients are in the balancedequation below:

F2 2KCl 2KF Cl2

Now It’s Your TurnWrite balanced equations forthe following:

HCl Na2S H2S NaClAl Cl2 AlCl3

MATH BREAK

Become a better balancer ofchemical equations on page

682 of the LabBook.

H2 + O2 2H2O

Reactants Products

To balance theoxygen atoms, placethe coefficient 2 infront of water’s for-mula. This gives you 2 oxygen atoms inboth the reactants andthe products. But nowthere are too few hydrogen atoms in the reactants.

2

H = 2 O = 2H = 4O = 2

2H2 + O2 2H2O

Reactants

To balance thehydrogen atoms,place the coefficient2 in front of hydro-gen’s formula. Butjust to be sure youranswer is correct,always double-check your work!

3

Products

H = 2 O = 2 H = 2O = 1

H = 4 O = 2H = 4O = 2


Mass Is Conserved—It’s a Law! The practice of balancingequations is a result of the work of a French chemist, AntoineLavoisier (luh vwa ZYAY). In the 1700s, Lavoisier performedexperiments in which he carefully measured and comparedthe masses of the substances involved in chemical reactions.He determined that the total mass of the reactants equaledthe total mass of the products. Lavoisier’s work led to the law of conservation of mass, which states that mass is neithercreated nor destroyed in ordinary chemical and physicalchanges. Thus, a chemical equation must show the same num-ber and kind of atom on both sides of the arrow. The law ofconservation of mass is demonstrated in Figure 12. You canexplore this law for yourself in the QuickLab at right.


1. List four clues that a chemical reaction is occurring.

2. How many atoms of each element make up 2Na3PO4?

3. Write the chemical formulas for carbon tetrachloride andcalcium bromide.

4. Explain how a balanced chemical equation illustrates thatmass is never lost or gained in a chemical reaction.

5. Applying Concepts Write the balanced chemical equa-tion for methane, CH4, reacting with oxygen gas to pro-duce water and carbon dioxide.

Figure 12 In this demonstration, magnesium in the flash-bulb of a camera reacts with oxygen. Notice that the massis the same before and after the reaction takes place.

REVIEW

Mass Conservation

1. Place 5 g (1 tsp) of baking sodainto a sealableplastic bag.

2. Place 5 mL (1 tsp) of vinegar into aplastic film canister.Close the lid.

3. Use a balance to deter-mine the masses of thebag with baking soda andthe canister with vinegar,and record both values inyour ScienceLog.

4. Place the canister into thebag. Squeeze the air out ofthe bag, and tightly seal it.

5. Open the canister in thebag. Mix the vinegar withthe baking soda.

6. When the reaction hasstopped, measure the totalmass of the bag and itscontents.

7. Compare the mass of thematerials before and afterthe reaction.

NSTA

TOPIC: Chemical Formulas, Chemical Equations


Chapter 14358

Types of Chemical ReactionsImagine having to learn 50 chemical reactions. Sound tough?Well, there are thousands of known chemical reactions. Itwould be impossible to remember them all. But there is help!Remember that the elements are divided into categories basedon their properties. In a similar way, reactions can be classi-fied according to their similarities.

Many reactions can be grouped into one of four categories:synthesis (SIN thuh sis), decomposition, single replacement,and double replacement. By dividing reactions into these cat-egories, you can better understand the patterns of how reac-tants become products. As you learn about each type ofreaction, study the models provided to help you recognizeeach type of reaction.

Synthesis ReactionsA synthesis reaction is a reaction in which two ormore substances combine to form a single compound.For example, the synthesis reaction in which thecompound magnesium oxide is produced is seen inFigure 13. (This is the same reaction that occurs in the flashbulb in Figure 12.) One way to rememberwhat happens in each type of reaction is to imaginepeople at a dance. A synthesis reaction would bemodeled by two people joining to form a dancingcouple, as shown in Figure 14.

Figure 14 A model for the synthesisreaction of sodium reacting with chlorineto form sodium chloride is shown below.

2Na + Cl2 2NaCl

+

Section

2

synthesis reactiondecomposition reactionsingle-replacement reactiondouble-replacement reaction

Describe four types of chemicalreactions.

Classify a chemical equation asone of the four types of chemi-cal reactions described here.

Figure 13 The synthesis reactionthat occurs when magnesiumreacts with oxygen in the airforms the compound magnesiumoxide.


Decomposition ReactionsA decomposition reaction is a reaction in which a singlecompound breaks down to form two or more simpler sub-stances. The decomposition of water is shown in Figure 15.Decomposition is the reverse of synthesis. The dance modelwould represent a decomposition reaction as a dancing cou-ple splitting up, as shown in Figure 16.

Single-Replacement ReactionsA single-replacement reaction is a reaction in which an el-ement takes the place of another element that is part of a com-pound. The products of single-replacement reactions are a newcompound and a different element. The dance model for single-replacement reactions is a person who cuts in on a coupledancing. A new couple is formed and a different person is leftalone, as shown in Figure 17.


Figure 15 Water can bedecomposed into theelements hydrogen andoxygen through electrolysis.

Figure 16 A model for the decomposition reaction of carbonicacid to form water and carbon dioxide is shown below.

Figure 17 A model for a single-replacement reaction of zincreacting with hydrochloric acid toform zinc chloride and hydrogenis shown below.

+

++

Zn + 2HCl ZnCl2 + H2

H2CO3 H2O + CO2


Some Elements Are More Reactive Than Others In a single-replacement reaction, a more-reactive element can replacea less-reactive one from a compound. However, the oppositereaction does not occur, as shown in Figure 18.

Double-Replacement ReactionsA double-replacement reaction is a reaction in which ions intwo compounds switch places. One of the products of thisreaction is often a gas or a precipitate. A double-replacementreaction in the dance model would be two couples dancingand switching partners, as shown in Figure 19.

Figure 18 More-reactive elementsreplace less-reactive elements insingle-replacement reactions.

Figure 19 A model for thedouble-replacement reaction ofsodium chloride reacting withsilver fluoride to form sodiumfluoride and the precipitate silverchloride is shown below.

Chapter 14360

1. What type of reaction does each of the following equa-tions represent?

a. FeS 2HCl FeCl2 H2S

b. NH4OH NH3 H2O

2. Which type of reaction always has an element and a com-pound as reactants?

3. Comparing Concepts Compare synthesis and decompo-sition reactions.

REVIEW

+ +

Cu + 2AgNO3 2Ag + Cu(NO3)2Copper is more reactive than silver.

Ag + Cu(NO3)2 No reactionSilver is less reactive than copper.

NaCl + AgF NaF + AgCl

NSTA

TOPIC: Reaction TypesGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP343



Figure 20 Types of Energy Released in Reactions

Light energy is released inthe exothermic reaction takingplace in these light sticks.

Electrical energy is releasedin the exothermic reactiontaking place in the dry cellsin this flashlight.

Light and thermal energy arereleased in the exothermicreaction taking place in thiscampfire.

Section

3

exothermicendothermiclaw of conservation of energyactivation energycatalystinhibitor

Compare exothermic andendothermic reactions.

Explain activation energy. Interpret an energy diagram. Describe the factors that affect

the rate of a reaction.

Energy and Rates of Chemical ReactionsYou just learned one method of classifying chemical reactions.In this section, you will learn how to classify reactions in termsof the energy associated with the reaction and learn how tochange the rate at which the reaction occurs.

Every Reaction Involves EnergyAll chemical reactions involve chemical energy. Remember thatduring a reaction, chemical bonds in the reactants break asthey absorb energy. As new bonds form in the products, energyis released. Energy is released or absorbed in the overall reac-tion depending on how the chemical energy of the reactantscompares with the chemical energy of the products.

Energy Is Released in Exothermic Reactions If the chemi-cal energy of the reactants is greater than the chemical energyof the products, the difference in energy is released during thereaction. A chemical reaction in which energy is released orremoved is called exothermic. Exo means “go out” or “exit,”and thermic means “heat” or “energy.” The energy can bereleased in several different forms, as shown in Figure 20. Theenergy released in an exothermic reaction is often written asa product in a chemical equation, as in this equation:

2Na Cl2 2NaCl energy



362 Chapter 14

Matches rubbing together in a box could provide theactivation energy to light a strike-anywhere match.Safety matches, which mustbe struck on a strike plateon the box, were developedto prevent such accidents.

Figure 21 Rubbing the tip of this strike-anywherematch on a rough surface provides the energyneeded to get the chemicals to react.


Photosynthesis is an endothermicprocess in which light energy from the sun is used to produce glucose, a simple sugar. The equation thatdescribes photosynthesis is as follows:

6CO2 6H2O energy

C6H12O6 6O2

The cells in your body use glucoseto get the energy they need throughcellular respiration, an exothermicprocess described by the reverse ofthe above reaction:

C6H12O6 6O2

6CO2 6H2O energy

Energy Is Absorbed in Endothermic Reactions If the chemi-cal energy of the reactants is less than the chemical energy ofthe products, the difference in energy is absorbed during thereaction. A chemical reaction in which energy is absorbed iscalled endothermic. Endo means “go in,” and thermic means“heat” or “energy.” The energy absorbed in an endothermicreaction is often written as a reactant in a chemical equation,as in this equation:

2H2O energy 2H2 O2

Energy Is Conserved—It’s a Law! You learned that mass isnever created or destroyed in chemical reactions. The sameholds true for energy. The law of conservation of energy statesthat energy can be neither created nor destroyed. The energyreleased in exothermic reactions was originally stored in thereactants. And the energy absorbed in endothermic reactionsdoes not just vanish. It is stored in the products that form. Ifyou could carefully measure all the energy in a reaction, youwould find that the total amount of energy (of all types) is thesame before and after the reaction.

Activation Energy Gets a Reaction Started A match canbe used to light a campfire—but only if the match is lit! Astrike-anywhere match, like the one shown in Figure 21, hasall the reactants it needs to be able to burn. And thoughthe chemicals on a match are intended to react and burn,

they will not ignite by themselves. Energy is neededto start the reaction. The minimum amount of

energy needed for substances to react is called activation energy.

The friction of striking a match heats the substances onthe match, breaking bonds in the reactants and allowing thenew bonds in the products to form. Chemical reactions requiresome energy to get started. An electric spark in a car’s engineprovides activation energy to begin the burning of gasoline.Light can also provide the activation energy for a reaction.You can better understand activation energy and the differ-ences between exothermic reactions and endothermic reac-tions by studying the diagrams in Figure 22.


Factors Affecting Rates of ReactionsYou can think of a reaction as occurring only if the particlesof reactants collide when they have enough energy to breakthe appropriate bonds. The rate of a reaction is a measure ofhow rapidly the reaction takes place. Four factors that affectthe rate of a reaction are temperature, concentration, surfacearea, and the presence of a catalyst or inhibitor.


Figure 22 Energy Diagrams

Ener

gy

Reaction progress

Reactants

Energy given off

Activation energy

Products

Ener

gy

Reactants

Energy absorbed

Activation energy

Products

Reaction progress

Fighting fires with slime? Readmore about it on page 370.

Exothermic Reaction Once begun, anexothermic reaction can continue to occur, as in a fire. The energy released as the prod-uct forms continues to supply the activationenergy needed for the substances to react.

Endothermic Reaction An endothermic reac-tion requires a continuous supply of energy.Energy must be absorbed to provide the activa-tion energy needed for the substances to react.

Fresh Hydrogen PeroxideHydrogen peroxide is used as a disinfectant for minorscrapes and cuts because it decomposes to produce oxy-gen gas and water, which help cleanse the wound. Thedecomposition of hydrogen peroxide is an exothermicreaction. Explain why hydrogen peroxide must be storedin a dark bottle to maintain its freshness. (HINT: What typeof energy would be blocked by this type of container?


Temperature An increase in temperature increases the rateof a reaction. At higher temperatures, particles of reactantsmove faster, so they collide with each other more frequentlyand with more energy. More particles therefore have the acti-vation energy needed to react and can change into productsfaster. Thus, more particles react in a shorter time. You cansee this effect in Figure 23 and by doing the QuickLab at left.

Concentration Generally, increasing the concentration of reac-tants increases the rate of a reaction, as shown in Figure 24.Concentration is a measure of the amount of one substance dis-solved in another. Increasing the concentration increases thenumber of reactant particles present and decreases the distancebetween them. The reactant particles collide more often, somore particles react each second. Increasing the concentrationis similar to having more people in a room. The more peoplethat are in the room, the more frequently they will collideand interact.

Chapter 14364

Figure 23 The light stick on the right glows brighter than the one on the left because the higher temperaturecauses the rate of the reaction to increase.

Figure 24 The reaction on the right produces bubblesof hydrogen gas at a faster rate because theconcentration of hydrochloric acid used is higher.

Do you feel as though you arenot up to speed on controlling

the rate of a reaction? Thenhurry over to page 686 of

the LabBook.

Which Is Quicker?

1. Fill a clear plasticcup half-full withwarm water. Fill asecond clear plasticcup half-full withcold water.

2. Place one-quarter of aneffervescent tablet ineach of the two cups ofwater at the same time.

3. Observe the reaction, andrecord your observations inyour ScienceLog.

4. In which cup did the reac-tion occur at a greater rate?What evidence supportsyour answer?


Surface Area Increasing the surface area, or the amount ofexposed surface, of solid reactants increases the rate of a reac-tion. Grinding a solid into a powder exposes more particles ofthe reactant to other reactant particles. The number of colli-sions between reactant particles increases, increasing the rateof the reaction. You can see the effect of increasing the sur-face area in the QuickLab at right.

Catalysts and Inhibitors Some reactions would be too slowto be useful without a catalyst (KAT uh LIST). A catalyst is asubstance that speeds up a reaction without being permanentlychanged. A catalyst lowers the activation energy of a reaction,which allows the reaction to occur more rapidly. Most reac-tions in your body are sped up using catalysts called enzymes.Catalysts are even found in cars, as seen in Figure 25.

An inhibitor is a substance that slows down or stops achemical reaction. Preservatives added to foods are inhibitorsthat slow down reactions in the bacteria or fungus that canspoil food. Many poisons are also inhibitors.


1. What is activation energy?

2. List four ways to increase therate of a reaction.

3. Comparing Concepts Compareexothermic and endothermicreactions.

4. Interpreting Graphics Doesthis energy diagram show anexothermic or an endothermicreaction? How can you tell?

REVIEW

Ener

gy

Reaction progress

Figure 25 This catalytic converter contains platinum and palladium—two catalysts that increase the rate of reactions that make the car’s exhaust less polluting.

I’m Crushed!

1. Fill two clear plasticcups half-full withroom-temperaturewater.

2. Fold a sheet ofpaper around one-quarterof an effervescent tablet.Carefully crush the tablet.

3. Get another one-quarter ofan effervescent tablet.Carefully pour the crushedtablet into one cup, andplace the uncrushed tabletin the second cup.

4. Observe the reaction, andrecord your observations inyour ScienceLog.

5. In which cup did the reac-tion occur at a greater rate?What evidence supportsyour answer?

6. Explain why the water ineach cup must have thesame temperature.

NSTA

TOPIC: Exothermic and EndothermicReactions


Chapter Highlights

Chapter 14366

SECTION 1 SECTION 2

Vocabularychemical reaction (p. 350)

chemical formula (p. 352)

chemical equation (p. 354)

reactants (p. 354)

products (p. 354)

law of conservation of mass (p. 357)

Section Notes

• Chemical reactions form newsubstances with differentproperties than the startingsubstances.

• Clues that a chemical reac-tion is taking place includeformation of a gas or solid, acolor change, and an energychange.

• A chemical formula tells thecomposition of a compoundusing chemical symbols andsubscripts. Subscripts aresmall numbers written belowand to the right of a symbolin a formula.

• Chemical formulas cansometimes be written fromthe names of covalentcompounds and ioniccompounds.

• A chemical equationdescribes a reaction usingformulas, symbols, andcoefficients.

• A balanced equation usescoefficients to illustrate thelaw of conservation of mass,that mass is neither creatednor destroyed during achemical reaction.

LabsFinding a Balance (p. 682)

Vocabularysynthesis reaction (p. 358)

decomposition reaction (p. 359)

single-replacement reaction (p. 359)

double-replacement reaction (p. 360)

Section Notes

• Many chemical reactions canbe classified as one of fourtypes by comparing reactantswith products.

• In synthesis reactions, thereactants form a singleproduct.

• In decomposition reactions,a single reactant breaks apartinto two or more simplerproducts.

Skills CheckMath ConceptsSUBSCRIPTS AND COEFFICIENTS A subscript isa number written below and to the right of achemical symbol when writing the chemicalformula of a compound. A coefficient is a num-ber written in front of a chemical formula in achemical equation. When you balance a chemi-cal equation, you cannot change the subscriptsin a formula; you can only add coefficients, asseen in the equation 2H2 O2 2H2O.

Visual UnderstandingREACTION TYPES It can be challenging to identifywhich type of reaction aparticular chemical equa-tion represents. Reviewfour reaction types bystudying Figures 14, 16, 17, and 19.


SECTION 3

• In single-replacementreactions, a more-reactiveelement takes the place of aless-reactive element in acompound. No reaction willoccur if a less-reactiveelement is placed with acompound containing amore-reactive element.

• In double-replacementreactions, ions in two com-pounds switch places. A gasor precipitate is oftenformed.

LabsPutting Elements Together (p. 684)

Vocabularyexothermic (p. 361)

endothermic (p. 362)

law of conservation of energy (p. 362)

activation energy (p. 362)

catalyst (p. 365)

inhibitor (p. 365)

Section Notes

• Energy is released in exother-mic reactions. The energyreleased can be written as aproduct in a chemicalequation.

• Energy is absorbed in endo-thermic reactions. Theenergy absorbed can bewritten as a reactant in achemical equation.

• The law of conservation ofenergy states that energy is neither created nordestroyed.

• Activation energy is theenergy needed to start achemical reaction.

• Energy diagrams indicatewhether a reaction isexothermic or endothermicby showing whether energyis given off or absorbed dur-ing the reaction.

• The rate of a chemical reac-tion is affected by tempera-ture, concentration, surfacearea, and the presence of acatalyst or inhibitor.

• Raising the temperature,increasing the concentration,increasing the surface area,and adding a catalyst canincrease the rate of areaction.

LabsCata-what? Catalyst! (p. 683)

Speed Control (p. 686)

SECTION 2


TOPIC: Chemical Reactions sciLINKS NUMBER: HSTP330

TOPIC: Chemical Formulas sciLINKS NUMBER: HSTP335

TOPIC: Chemical Equations sciLINKS NUMBER: HSTP340

TOPIC: Reaction Types sciLINKS NUMBER: HSTP343

TOPIC: Exothermic and sciLINKS NUMBER: HSTP345Endothermic Reactions



KEYWORD: HSTREA

Chemical Reactions 367Copyright © by Holt, Rinehart and Winston. All rights reserved.


To complete the following sentences, choosethe correct term from each pair of terms listedbelow.

1. Adding a(n) ____ will slow down a chemi-cal reaction. (catalyst or inhibitor)

2. A chemical reaction that gives off light iscalled ____. (exothermic or endothermic)

3. A chemical reaction that forms one com-pound from two or more substances iscalled a ____. (synthesis reaction or decom-position reaction)

4. The 2 in the formula Ag2S is a ____.(subscript or coefficient)

5. The starting materials in a chemical reac-tion are ____. (reactants or products)


Multiple Choice

6. Balancing a chemical equation so that thesame number of atoms of each element is found in both the reactants and theproducts is an illustration ofa. activation energy.b. the law of conservation of energy.c. the law of conservation of mass.d.a double-replacement reaction.

7. What is the correct chemical formula forcalcium chloride?a. CaCl c. Ca2Clb. CaCl2 d.Ca2Cl2

8. In which type of reaction do ions in twocompounds switch places?a. synthesisb. decompositionc. single-replacementd.double-replacement

9. Which is an example of the use of activa-tion energy?a. plugging in an ironb. playing basketballc. holding a lit match to paperd.eating

10. Enzymes in your body act as catalysts.Thus, the role of enzymes is toa. increase the rate of chemical reactions.b. decrease the rate of chemical reactions.c. help you breathe.d. inhibit chemical reactions.

Short Answer

11. Classify each of the following reactions:a. Fe O2 Fe2O3

b. Al CuSO4 Al2(SO4)3 Cuc. Ba(CN)2 H2SO4 BaSO4 HCN

12. Name two waysthat you couldincrease the rateof a chemicalreaction.

13. Acetic acid, a compound found invinegar, reacts with baking soda to produce carbon dioxide, water, andsodium acetate. Without writingan equation, identify the reactants and the products of this reaction.

Chapter 14368


Concept Mapping

14. Use the followingterms to create aconcept map:chemical reaction,chemical equation,chemical formulas,reactants, products,coefficients, subscripts.


15. Your friend is very worried by rumors hehas heard about a substance called dihy-drogen monoxide. What could you say toyour friend to calm his fears? (Be sure towrite the formula of the substance.)

16. As long as proper safety precautions havebeen taken, why can explosives be trans-ported long distances without exploding?

MATH IN SCIENCE

17. Calculate the number of atoms of eachelement shown in each of the following:a. CaSO4

b. 4NaOClc. Fe(NO3)2

d.2Al2(CO3)3

18. Write balanced equations for the following:a. Fe O2 Fe2O3

b. Al CuSO4 Al2(SO4)3 Cuc. Ba(CN)2 H2SO4 BaSO4 HCN

19. Write and balance chemical equationsfrom each of the following descriptions:a. Bromine reacts with sodium iodide to

form iodine and sodium bromide.b. Phosphorus reacts with oxygen gas to

form diphosphorus pentoxide.c. Lithium oxide decomposes to form

lithium and oxygen.


20. What evidence in the photo supports the claim that a chemical reaction istaking place?

21. Use the energy diagram below to answerthe questions that follow.

a. Which letter represents the energy ofthe products?

b. Which letter represents the activationenergy of the reaction?

c. Is energy given off or absorbed by thisreaction?

Ener

gy

Reaction progress

A

D

B

C




ReadingCheck-up


is applied, firefighters on the ground can gainvaluable time when a fire is slowed with a fireretardant. This extra time allows them to createa fire line that will ultimately stop the fire.

Neon Isn’t NecessaryOnce a fire is put out, the slimy red streaks lefton the blackened ground can be an eyesore. Tosolve the problem, scientists have created spe-cial dyes for the retardant. These dyes make thegoop neon colors when it is first applied, butafter a few days in the sun, the goop turns anatural brown shade!

What Do They Study? Do some research to learn about a fire-fighter’s training. What classes and exams are firefighters required to pass? Howdo they maintain their certificationsonce they become firefighters?

Slime That Fire!Once a fire starts in the hard-to-reachmountains of the western United States,it is difficult to stop. Trees, grasses, andbrush can provide an overwhelming sup-ply of fuel. In order to stop a fire, fire-fighters make a fire line. This is an areawhere all the burnable materials areremoved from the ground. How wouldyou slow down a fire to give a groundcrew more time to build a fire line?Would you suggest dropping water froma plane? That is not a bad idea, but whatif you had something even better thanwater—like some slimy red goop?

Red Goop Goes the DistanceThe slimy red goop is actually a powerful fire retardant. The goop is a mixture of a pow-der and water that is loaded directly onto an old military plane. Carrying between 4,500 and11,000 L of the slime, the plane drops it all in front of the raging flames when the pilotpresses the button.

The amount of water added to the powderdepends on the location of the fire. If a fire is

burning over shrubs and grasses, morewater is needed. In this form the goop actu-

ally rains down to the ground through thetreetops. But if a fire is burning in tall trees,

less water is used so the slime will glob ontothe branches and ooze down very slowly.

Failed FlamesThe burning of trees, grass, and brush is anexothermic reaction. A fire retardant slows orstops this self-feeding reaction. A fire retardantincreases the activation energy for the materialsit is applied to. Although a lot depends on howhot the fire is when it hits the area treated withthe retardant and how much of the retardant

This plane is dropping fire retardant on aforest fire.


During a fire, fuel and oxygen combine in a chemical reactioncalled combustion. On the scene, Lt. Larry McKee questions

witnesses and firefighters about what they saw. He knows, forexample, that the color of the smoke can indicate certain chemicals.

McKee explains that fires usually burn “up and out, in a Vshape.“ To find where the V begins, he says, “We work from thearea with the least amount of damage to the one with the mostdamage. This normally leads us to the point of origin.“ Once theorigin has been determined, it's time to call in the dogs!

An Accelerant-Sniffing Canine“We have what we call an accelerant-sniffing canine. Our canine,Nikki, has been trained to detect approximately 11 different chemi-cals.“ When Nikki arrives on the scene, she sniffs for traces ofchemicals, called accelerants, that may have been used to start thefire. When she finds one, she immediately starts to dig at it. At thatpoint, McKee takes a sample from the area and sends it to the lab for analysis.

At the LabOnce at the laboratory, the sample is treated so that any accelerantsin it are dissolved in a liquid. A small amount of the liquid is theninjected into an instrument called a gas chromatograph. The instru-

Once a fire dies down, youmight see arson investigatorLt. Larry McKee on thescene. “After the fire is out, Ican investigate the fire sceneto determine where the firestarted and how it started. Ifit was intentionally set andI'm successful at putting thearson case together, I can geta conviction. That's verysatisfying,” says Lt. McKee.

A R S O N I N V E S T I G AT O R

ment heats the liquid, forming a mixture of gases. Thegases then are passed through a flame. As each gaspasses through the flame, it “causes a fluctuation in anelectronic signal, which creates our graphs.”

Solving the CaseIf the laboratory report indicates that a suspicious accel-erant has been found, McKee begins to search for arsonsuspects. By combining detective work with scientificevidence, fire investigators can successfully catch andconvict arsonists.

Fascinating Fire Facts The temperature of a house fire can reach 980°C! Atthat temperature, aluminum window frames melt, andfurniture goes up in flames. Do some research to dis-cover three more facts about fires. Create a display withtwo or more classmates to illustrate some of your facts.

Nikki searches for traces of gasoline,kerosene, and other accelerants.


372 Chapter 15

Ionic and CovalentCompounds . . . . . . . . . 374


Acids, Bases, and Salts . . . . . . . . . . . 377

QuickLab . . . . . . . . . . 380Biology Connection . . 381Internet Connect . . . . 382

Organic Compounds . . 383Biology Connection . . 386Internet Connect . . . . 389

Chapter Review . . . . . . . . . . 392


LabBook . . . . . . . . . . . . 688–691

ChemicalCompoundsChemicalCompounds

Something’s FishySome people keep saltwater aquariums as a hobby. The liv-ing organisms in these aquariums—fish, coral, and algae—must have the correct environment, or they might die.Many things must be controlled in the aquarium. Forexample, the pH of the water must stay within a certainrange. The amount of salt and other compounds in thewater also must be within a certain range. In this chapter,you will learn about pH. You will also learn about salts andother chemical compounds.


1. What is the differencebetween ionic compoundsand covalent compounds?

2. What is an acid?3. What is a hydrocarbon?


373

STICKING TOGETHERIn this activity you will demonstratethe force that keeps particlestogether in some compounds.

Procedure

1. Blow up two balloons. Rub themwith a piece of wool cloth.

2. Hold the balloons by their necks.Move the balloons near eachother. Describe in your ScienceLogwhat you see.

3. Put one of the balloons against awall. Record your observations inyour ScienceLog.

Analysis

4. The balloons are charged by rub-bing them with the wool cloth.Like charges repel each other.Opposite charges attract eachother. Infer whether the balloonshave like or opposite charges.Explain your answer.

5. The two types of charge are nega-tive and positive. The balloon instep 3 has a negative charge. Inferwhat the charge is on the wallwhere you put the balloon. Explain.

6. The particles that make up somecompounds are attracted to eachother in the same way that the bal-loon is attracted to the wall. Whatcan you infer about the particles thatmake up such compounds?

Chemical CompoundsCopyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 15374

Ionic and CovalentCompoundsThe world around you is made up of chemical compounds.Chemical compounds are pure substances composed of ionsor molecules. There are millions of different kinds of com-pounds, so you can imagine how classifying them might behelpful. One simple way to classify compounds is by group-ing them according to the type of bond they contain.

Figure 2 Ionic compounds will shatter when hit with a hammer.

Ionic CompoundsCompounds that contain ionic bonds arecalled ionic compounds. Remember thatan ionic bond is the force of attractionbetween two oppositely charged ions.Ionic compounds can be formed by thereaction of a metal with a nonmetal.Electrons are transferred from the metalatoms (which become positively chargedions) to the nonmetal atoms (whichbecome negatively charged ions). Forexample, when sodium reacts with chlo-rine, as shown in Figure 1, the ionic com-pound sodium chloride, or ordinary tablesalt, is formed.

Brittleness The forces acting betweenthe ions that make up ionic compoundsgive these compounds certain properties.Ionic compounds tend to be brittle, asshown in Figure 2. The ions that make up an ionic compound are arranged in a repeating three-dimensional patterncalled a crystal lattice. The ions that makeup the crystal lattice are arranged as alter-nating positive and negative ions. Eachion in the lattice is surrounded by ionsof the opposite charge, and each ion isbonded to the ions around it. When anionic compound is struck with a hammer,the pattern of ions in the crystal lattice isshifted. Ions with the same charge line upand repel one another, causing the crys-tal to shatter.

Section

1

ionic compoundscovalent compounds

Describe the properties of ionicand covalent compounds.

Classify compounds as ionic or covalent based on their properties.

Figure 1 An ionic com-pound is formed whenthe metal sodium reactswith the nonmetalchlorine. Sodium chlo-ride is formed in thereaction, and energy isreleased as light andthermal energy.


High Melting Points Ionic com-pounds are almost always solid atroom temperature, as shown inFigure 3. An ionic compound willmelt only at temperatures highenough to overcome the strongionic bonds between the ions.Sodium chloride, for instance,must be heated to 801°C before itwill melt. This temperature ismuch higher than you can pro-duce in your kitchen or even yourschool laboratory.

Solubility and Electrical Conductivity Many ionic com-pounds dissolve easily in water. Molecules of water attract eachof the ions of an ionic compound and pull them away fromone another. The solution created when an ionic compounddissolves in water can conduct an electric current, as shownin Figure 4. The ions are able to move past one another andconduct the electric current in the solution. Keep in mind thatan undissolved crystal of an ionic compound does not conductan electric current.

Covalent CompoundsCompounds composed of elements that are covalently bondedare called covalent compounds. Remember that covalent bonds form when atoms share electrons. Gasoline, carbondioxide, water, and sugar are well-known examples of cova-lent compounds.

Chemical Compounds 375

Figure 3 Each of these ioniccompounds has a high meltingpoint and is solid at room temperature.

Nickel(II) oxidemelts at 1,984°C.

Magnesium oxidemelts at 2,800°C.

Potassium dichromatemelts at 398°C.

Pure water Salt water

Figure 4 The pure water in the left beaker does not conduct an electric current. The solution of salt water in the right beakerconducts an electric current, and the bulb lights up.


Low Melting Points Covalent compounds exist as independ-ent particles called molecules. The forces of attraction betweenmolecules of covalent compounds are much weaker than thebonds between ions in a crystal lattice. Thus, covalent com-pounds have lower melting points than ionic compounds.

Solubility and Electrical Conductivity You have probablyheard the phrase “oil and water don’t mix.” Oil, such as thatused in salad dressing, is composed of covalent compounds.Many covalent compounds do not dissolve well in water. Watermolecules have a stronger attraction for one another than theyhave for the molecules of most other covalent compounds.Thus, the molecules of the covalent compound get squeezedout as the water molecules pull together. Some covalent com-pounds do dissolve in water. Most of these solutions containuncharged molecules dissolved in water and do not conductan electric current, as shown in Figure 5. Some covalent com-pounds form ions when they dissolve in water. Solutions ofthese compounds, including compounds called acids, do con-duct an electric current. You will learn more about acids inthe next section.

Chapter 15376

1. List two properties of ionic compounds.

2. List two properties of covalent compounds.

3. Methane is a gas at room temperature. What type of com-pound is this most likely to be?

4. Comparing Concepts Compare ionic and covalentcompounds based on the type of particle that makesup each.

Figure 5 This solution of sugar, acovalent compound, in water doesnot conduct an electric currentbecause the individual moleculesof sugar are not charged.

Molecules of covalent com-pounds can have anywherefrom two atoms to hundredsor thousands of atoms!Small, lightweight mol-ecules, like water or carbondioxide, tend to form liquidsor gases at room tempera-ture. Heavier molecules,such as sugar or plastics,tend to form solids at roomtemperature.

REVIEW

Sugar water

NSTA

TOPIC: Ionic Compounds, Covalent Compounds



Figure 7 Bubbles of hydrogen gas are produced when zinc metal reacts with hydrochloric acid.


Acids, Bases, and SaltsHave you ever noticed that when yousqueeze lemon juice into tea, the colorof the tea becomes lighter? Shown inFigure 6, lemon juice contains a sub-stance called an acid that changesthe color of a substance in thetea. The ability to change thecolor of certain chemicals is oneproperty used to classify sub-stances as acids or bases. A thirdcategory of substances, calledsalts, are formed by the reac-tion of an acid with a base.

AcidsAn acid is any compound that increases the number of hydro-gen ions when dissolved in water, and whose solution tastessour and can change the color of certain compounds.

Properties of Acids If you have ever had orange juice, youhave experienced the sour taste of an acid. The taste of lemons,limes, and other citrus fruits is a result of citric acid. Taste,however, should NEVER be used as a test to identify an unknownchemical. Many acids are corrosive, meaning they destroy bodytissue and clothing, and many are also poisonous.

Acids react with some metals to produce hydrogen gas, asshown in Figure 7. Adding an acid to baking soda or limestoneproduces a different gas, carbon dioxide.

Solutions of acids conduct an electric current because acidsbreak apart to form ions in water. Acids increase the numberof hydrogen ions, H+, in a solution. However, the hydrogen iondoes not normally exist alone. In a water solution, each hydro-gen ion bonds to a water molecule, H2O, to form a hydroniumion, H3O+.

NEVER touch or taste

a concentrated solution of astrong acid.

Section

2

acid pHbase salt

Describe the properties and usesof acids and bases.

Explain the difference betweenstrong acids and bases andweak acids and bases.

Identify acids and bases usingthe pH scale.

Describe the properties and usesof salts.

Figure 6 Acids, like thosefound in lemon juice, canchange the color of tea.


Detecting Acids As mentioned earlier, a property of acids istheir ability to change the color of a substance. An indicatoris a substance that changes color in the presence of an acidor base. An indicator commonly used is litmus. Paper stripscontaining litmus are available in both blue and red. Whenan acid is added to blue litmus paper,the color of the litmus changes tored, as shown in Figure 8. (Red lit-mus paper is used to detect bases,as will be discussed shortly.) Manyplant materials, such as red cab-bage, contain compounds thatare indicators.

Uses of Acids Acids are used in many areas ofindustry as well as in your home. Sulfuric acid isthe most widely produced industrial chemical inthe world. It is used in the production of metals,paper, paint, detergents, and fertilizers. It is alsoused in car batteries, as shown in Figure 9. Nitricacid is used to make fertilizers, rubber, and plas-tics. Hydrochloric acid is used in the productionof metals and to help keep swimming pools freeof algae. It is also found in your stomach, whereit aids in digestion. Citric acid and ascorbic acid(vitamin C) are found in orange juice, while car-bonic acid and phosphoric acid help give extra“bite” to soft drinks.

Strong Versus Weak As an acid dissolves in water, its mol-ecules break apart and produce hydrogen ions. When all themolecules of an acid break apart in water to produce hydrogenions, the acid is considered a strong acid. Strong acids includesulfuric acid, nitric acid, and hydrochloric acid.

When few molecules of an acid break apart in water toproduce hydrogen ions, the acid is considered a weak acid.Acetic acid, citric acid, carbonic acid, and phosphoric acid areall weak acids.

Chapter 15378

Some hydrangea plants actas indicators. Leaves on theplants change from pink toblue as the soil becomesmore acidic.

Figure 8 Vinegar turns blue litmuspaper red because it containsacetic acid.

Figure 9 The label on this carbattery warns you that sulfuricacid is found in the battery.


BasesA base is any compound that increases the number of hydrox-ide ions when dissolved in water, and whose solution tastes bit-ter, feels slippery, and can change the color of certain compounds.

Properties of Bases If you have ever accidentally tasted soap,then you know the bitter taste of a base. Soap also demon-strates that a base feels slippery. However, NEVER use taste ortouch as a test to identify an unknown chemical. Like acids,many bases are corrosive. If your fingers feel slippery when youare using a base in an experiment, you might have gotten thebase on your hands. You should immediately rinse your handswith large amounts of water.

Solutions of bases conduct an electric current because basesincrease the number of hydroxide ions, OH, in a solution. Ahydroxide ion is actually a hydrogen atom and an oxygen atombonded together. An extra electron gives the ion a negative charge.

Detecting Bases Like acids, baseschange the color of an indicator. Mostindicators turn a different color for basesthan they do for acids. For example,bases will change the color of red litmuspaper to blue, as shown in Figure 10.

Uses of Bases Like acids, bases have many uses. Sodiumhydroxide is used to make soap and paper. It is also in ovencleaners and in products that unclog drains, as shown inFigure 11. Remember, bases can harm your skin, so carefullyfollow the safety instructions when using these products.Calcium hydroxide is used to make cement, mortar, and plas-ter. Ammonia is found in many household cleaners and is alsoused in the production of fertilizers. Magnesiumhydroxide and aluminum hydroxide areused in antacids to treat heartburn.

379

To determine how acidic orbasic a solution is, just use your head—of cabbage! Try it for yourself on page 688 of the LabBook.

NEVER touch or taste

a concentrated solution of astrong base.

Figure 10 Sodium hydroxide,a base, turns red litmuspaper blue.

Figure 11 This drain cleanercontains sodium hydroxide tohelp dissolve grease that can clog the drain.


Strong Versus Weak When all the molecules of a base breakapart in water to produce hydroxide ions, the base is called astrong base. Strong bases include sodium hydroxide, calciumhydroxide, and potassium hydroxide.

When only a few of the molecules of a base producehydroxide ions in water, the base is called a weak base.Ammonia, magnesium hydroxide, and aluminum hydroxideare all weak bases.

Acids and Bases Neutralize One AnotherIf you have ever suffered from an acid stomach, or heartburn,as shown in Figure 12, you might have taken an antacid.Antacids contain weak bases that soothe your heartburn byreacting with and neutralizing the acid in your stomach. Acidsand bases neutralize one another because the H of the acidand the OH of the base react to form water, H2O. Other ionsfrom the acid and base are also dissolved in the water. If thewater is evaporated, these ions join to form a compound calleda salt. You’ll learn more about salts later in this section.

The pH Scale Indicators such as litmus can identify whethera solution contains an acid or base. To describe how acidic orbasic a solution is, the pH scale is used. The pH of a solutionis a measure of the hydronium ion concentration in the solu-tion. By measuring the hydronium ion concentration, the pHis also a measure of the hydrogen ion concentration. On thescale, a solution that has a pH of 7 is neutral, meaning thatit is neither acidic nor basic. Pure water has a pH of 7. Basicsolutions have a pH greater than 7, and acidic solutions havea pH less than 7. Look at Figure 13 to see the pH values formany common materials.

Chapter 15380

Increasing acidity Increasing basicity

Lemonjuice

Softdrink

Humansaliva

Tap water

Acid rain Clean rain

Human stomach contents

Seawater

Detergents Householdammonia

Milk

1 2 3 4 5 6 7 8 9 10 11 12 13

Figure 12 Have heartburn? Takean antacid! Antacid tablets con-tain a base that neutralizes theacid in your stomach.

Figure 13 pH Values of Common Materials

pHast Relief!

1. Fill a small plastic cup halfway with vinegar. Test the vinegar with redand blue litmus paper. Record your results in your ScienceLog.

2. Carefully crush an antacidtablet, and mix it with thevinegar. Test the mixturewith litmus paper. Recordyour results in yourScienceLog.

3. Compare the acidity of thesolution before and afterthe reaction.


Self-CheckWhich is more acidic, a soft drink or milk? (Hint:Refer to Figure 13 to find the pH values of thesedrinks.) (See page 724 to check your answer.)


Human blood has a pH of between7.38 and 7.42. If the pH is above 7.8or below 7, the body cannot functionproperly. Sudden changes in bloodpH that are not quickly corrected canbe fatal.

Using Indicators to Determine pH A singleindicator allows you to determine if a solutionis acidic or basic, but a mixture of differentindicators can be used to determine the pH ofa solution. After determining the colors forthis mixture at different pH values, the indi-cators can be used to determine the pH of anunknown solution, as shown in Figure 14.Indicators can be used as paper strips or solu-tions, and they are often used to test the pH ofsoil and of water in pools and aquariums. Anotherway to determine the acidity of a solution is to usean instrument called a pH meter, which can detectand measure hydrogen ions electronically.

pH and the Environment Living things depend on hav-ing a steady pH in their environment. Plants are knownto have certain preferred growing conditions. Some plants,such as pine trees, prefer acidic soil with a pH between 4and 6. Other plants, such as lettuce, require basic soil witha pH between 8 and 9. Fish require water near pH 7.As you can see in Figure 13, rainwater can havea pH as low as 3. This occurs in areas wherecompounds found in pollution react with water to make the strong acidssulfuric acid and nitric acid. As this acid precipitation collects in lakes, it can lower the pH to levels thatmay kill the fish and other organ-isms in the lake. To neutralize theacid and bring the pH closer to 7, a base can be added to the lakes, as shown in Figure 15.

Figure 14 The paper strip containsseveral indicators. The pH of a solutionis determined by comparing the colorof the strip to the scale provided.

Figure 15 This helicopter is adding abase to an acidic lake. Neutralizing theacid in the lake might help protect theorganisms living in the lake.

Chemical Compounds 381Copyright © by Holt, Rinehart and Winston. All rights reserved.

SaltsWhen you hear the word salt, you probably think of the tablesalt you use to season your food. But the sodium chloridefound in your salt shaker is only one example of a large groupof compounds called salts. A salt is an ionic compound formedfrom the positive ion of a base and the negative ion of anacid. You may remember that a salt and water are producedwhen an acid neutralizes a base. However, salts can also beproduced in other reactions, as shown in Figure 16.

Uses of Salts Salts have many uses in industry and in yourhome. You already know that sodium chloride is used to sea-son foods. It is also used in the production of other com-pounds, including lye (sodium hydroxide), hydrochloric acid,and baking soda. The salt calcium sulfate is made into wall-board, or plasterboard, which is used in construction. Sodiumnitrate is one of many salts used as a preservative in foods.Calcium carbonate is a salt that makes up limestone, chalk,and seashells. Another use of salts is shown in Figure 17.

Figure 16 The salt potassiumchloride can be formed fromseveral different reactions.

Chapter 15382

1. What ion is present in all acid solutions?

2. What are two ways scientists can measure pH?

3. What products are formed when an acid and base react?

4. Comparing Concepts Compare the properties of acids andbases.

5. Applying Concepts Would you expect the pH of a solutionof soap to be 4 or 9?

REVIEW

Figure 17 Salts are used to helpkeep roads free of ice.

NSTA

TOPIC: Acids and Bases, SaltsGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP365, HSTP370


Figure 18 These models, called structural formulas, are usedto show how atoms in a molecule are connected. Each linerepresents a pair of electrons shared in a covalent bond.


Organic CompoundsOf all the known compounds, more than 90 percent are mem-bers of a group of compounds called organic compounds.Organic compounds are covalent compounds composed ofcarbon-based molecules. Sugar, starch, oil, protein, nucleic acid,and even cotton and plastic are organic compounds. How canthere be so many different kinds of organic compounds? Thehuge variety of organic compounds is explained by examin-ing the carbon atom.

Each Carbon Atom Forms Four BondsCarbon atoms form the backbone of organic compounds.Because each carbon atom has four valence electrons (elec-trons in the outermost energy level of an atom), each atomcan make four bonds. Thus, a carbon atom can bond to one,two, or even three other carbon atoms and still have electronsremaining to bond to other atoms. Three types of carbon back-bones on which many organic compounds are based are shownin the models in Figure 18.

Some organic compounds have hundreds or even thou-sands of carbon atoms making up their backbone! Althoughthe elements hydrogen and oxygen, along with carbon, makeup many of the organic compounds, sulfur, nitrogen, andphosphorus are also important—especially in forming the mol-ecules that make up all living things.

C HHC HHCH

HH

C HHC HHCH

HH

CHC HHCH

HH

CC HH

HHHCH

HH

CC

CC

C

HH H

H

HH

HH

H

H

H H

C

Straight Chain All carbonatoms are connected oneafter another in a line.

Branched Chain The chain of carbonatoms continues in more than one direc-tion where a carbon atom bonds to threeor more other carbon atoms.

Ring The chain of carbonatoms forms a ring.

Section

3

organic compoundsbiochemicals proteinscarbohydrates nucleic acidslipids hydrocarbons

Explain why so many organiccompounds are possible.

Describe the characteristics ofcarbohydrates, lipids, proteins,and nucleic acids and their func-tions in the body.

Describe and identify saturated,unsaturated, and aromatichydrocarbons.


Figure 19 The sugar moleculesin the left image are simple carbohydrates. The starch in theright image is a complex carbo-hydrate because it is composedof many sugar moleculesbonded together.

Biochemicals: The Compounds of LifeOrganic compounds made by living things are calledbiochemicals. The molecules of most biochemicals are verylarge. Biochemicals can be divided into four categories: carbo-hydrates, lipids, proteins, and nucleic acids. Each type ofbiochemical has important functions in living organisms.

Carbohydrates Starch and cellulose are examples of carbo-hydrates. Carbohydrates are biochemicals that are composedof one or more simple sugars bonded together; they are usedas a source of energy and for energy storage. There are twotypes of carbohydrates: simple carbohydrates and complexcarbohydrates. A single sugar molecule, represented using ahexagon, or a few sugar molecules bonded together are exam-ples of simple carbohydrates, as illustrated in Figure 19.Glucose is a simple carbohydrate produced by plants throughphotosynthesis.

Sugar Storage System When an organism has more sugarthan it needs, its extra sugar may be stored for later use inthe form of complex carbohydrates, as shown in Figure 19.

Molecules of complex carbohydrates are composed ofhundreds or even thousands of sugar molecules

bonded together. Because carbohydrates providethe energy you need each day, you should

include sources of carbohydrates in yourdiet, such as the foods shown in Figure 20.

Figure 20 Simple carbohydratesinclude sugars found in fruits andhoney. Complex carbohydrates,such as starches, are found inbread, cereal, and pasta.


Lipids Fats, oils, waxes, and steroids are examplesof lipids. Lipids are biochemicals that do notdissolve in water and have many differentfunctions, including storing energy andmaking up cell membranes. Althoughtoo much fat in your diet can beunhealthy, some fat is extremelyimportant to good health. The foodsin Figure 21 are sources of lipids.

Lipids store excess energy in thebody. Animals tend to store lipidsprimarily as fats, while plants storelipids as oils. When an organism hasused up most of its carbohydrates, itcan obtain energy by breaking downlipids. Lipids are also used to store vitaminsthat dissolve in fat but not in water.

Lipids Make Up Cell Membranes Each cell is surroundedby a cell membrane. Much of the cell membrane is formedfrom molecules of phospholipids. The structure of these mol-ecules plays an important part in the phospholipid’s role inthe cell membrane. The tail of a phospholipid molecule is along, straight-chain carbon backbone composed only of car-bon and hydrogen atoms. The tail is not attracted to water.The head of a phospholipid molecule is attracted to waterbecause it is composed of phosphorus, oxygen, and nitrogenatoms in addition to carbon and hydrogen atoms. This resultsin the double layer of phospholipid molecules shown in themodel in Figure 22. This arrangement of phospholipid mol-ecules creates a barrier to help control the flow of chemicalsinto and out of the cell.


Figure 22 A cell membrane iscomposed primarily of two layersof phospholipid molecules.

Deposits of the lipid choles-terol in the body have beenlinked to health problemssuch as heart disease.However, cholesterol isneeded in nerve and braintissue as well as to makecertain hormones that regu-late body processes such as growth.

The head of each phospholipidmolecule is attracted to watereither inside or outside of the cell.

The tail of each phospholipidmolecule is pushed againstother tails because they arenot attracted to water.

Figure 21 Vegetable oil, meat,cheese, nuts, and milk aresources of lipids in your diet.


Chapter 15386

Proteins Most of the biochemicals found in living things areproteins. In fact, after water, proteins are the most abundant

molecules in your cells. Proteins are biochemicals that arecomposed of amino acids; they have many different

functions, including regulating chemical activities,transporting and storing materials, and providingstructural support.

Every protein is composed of small “buildingblocks” called amino acids. Amino acids are smallermolecules composed of carbon, hydrogen, oxygen,

and nitrogen atoms. Some amino acids also includesulfur atoms. Amino acids chemically bond to form

proteins of many different shapes and sizes. The func-tion of a protein depends on the shape that the bonded

amino acids adopt. If even a single amino acid is missing orout of place, the protein may not function correctly or at all.The foods shown in Figure 23 provide amino acids that yourbody needs to make new proteins.

Examples of Proteins Enzymes are proteins that regulatechemical reactions in the body by acting as catalysts to increasethe rate at which the reactions occur. Some hormones are pro-teins. Insulin is a hormone that helps regulate the level of sugarin your blood. Oxygen is carried by the protein hemoglobin,allowing red blood cells to deliver oxygen throughout yourbody. There are also large proteins that extend through cellmembranes and help control the transport of materials intoand out of cells. Proteins that provide structural support oftenform structures that are easy to see, like those in Figure 24.

Figure 24 Hair andspider webs aremade up of proteinsthat are shaped likelong fibers.

Figure 23 Meat, fish, cheese,and beans contain proteins,which are broken down intoamino acids as they are digested.


All the proteins in your body aremade from just 20 amino acids.Nine of these amino acids are calledessential amino acids because yourbody cannot make them. You mustget them from the food you eat.



Nucleic Acids The largest molecules made by living organ-isms are nucleic acids. Nucleic acids are biochemicals that storeinformation and help to build proteins and other nucleic acids.Nucleic acids are sometimes called the “blueprints of life”because they contain all the information needed for the cellto make all of its proteins.

Like proteins, nucleic acids are long chains of smaller mol-ecules joined together. These smaller molecules are composedof carbon, hydrogen, oxygen, nitrogen, and phosphorus atoms.Nucleic acids are much larger than proteins even thoughnucleic acids are composed of only five building blocks.

DNA and RNA There are two types of nucleic acids: DNAand RNA. DNA (deoxyribonucleic acid), like that shown inFigure 25, is the genetic material of the cell. DNA moleculescan store an enormous amount of information because oftheir length. The DNA molecules in a singlehuman cell have an overall length ofabout 2 m—that’s over 6 ft long! Whena cell needs to make a certain pro-tein, it copies the important partof the DNA. The informationcopied from the DNA directsthe order in which amino acidsare bonded together to makethat protein. DNA also containsinformation used to build thesecond type of nucleic acid, RNA(ribonucleic acid). RNA is involvedin the actual building of proteins.

1. What are organic compounds?

2. What are the four categories of biochemicals?

3. What are two functions of proteins?

4. What biochemicals are used to provide energy?

5. Inferring Relationships Sickle-cell anemia is a conditionthat results from a change of one amino acid in the protein hemoglobin. Why is this condition a genetic disorder?

REVIEW

Figure 25 The DNA from a fruit fly contains all of theinstructions for making proteins,nucleic acids . . . in fact, for

making everything in the organism!

Nucleic acids store information—evenabout ancient peoples. Read moreabout these incredible biochemicalson page 394.



HydrocarbonsOrganic compounds that are composed of only carbon andhydrogen are called hydrocarbons. Hydrocarbons are an impor-tant group of organic compounds. Many fuels, including gaso-line, methane, and propane, are hydrocarbons. Hydrocarbonscan be divided into three categories: saturated, unsaturated,and aromatic.

Saturated Hydrocarbons Propane, like that used in the stovein Figure 26, is an example of a saturated hydrocarbon. Asaturated hydrocarbon is a hydrocarbon in which each carbonatom in the molecule shares a single bond with each of four

other atoms. A single bond is a covalent bond that con-sists of one pair of shared electrons. Hydrocarbons

that contain carbon atoms connected only by sin-gle bonds are called saturated because no otheratoms can be added without replacing an atomthat is part of the molecule. Saturated hydrocar-bons are also called alkanes.

Unsaturated Hydrocarbons Each carbon atom forms fourbonds. However, these bonds do not always have to be sin-gle bonds. An unsaturated hydrocarbon is a hydrocarbon inwhich at least two carbon atoms share a double bond or atriple bond. A double bond is a covalent bond that consistsof two pairs of shared electrons. Compounds that containtwo carbon atoms connected by a double bond are calledalkenes.

A triple bond is a covalent bond that consists of threepairs of shared electrons. Hydrocarbons that contain two car-bon atoms connected by a triple bond are called alkynes.

Hydrocarbons that contain double or triple bonds arecalled unsaturated because the double or triple bond can bebroken to allow more atoms to be added to the molecule.Examples of unsaturated hydrocarbons are shown in Figure 27.

Chapter 15388

CCHHH

H

CH C H

Figure 27 Fruits produce ethene,which helps ripen the fruit. Ethyne,better known as acetylene, isburned in this miner’s lamp and isalso used in welding.

Figure 26 The propane in thiscamping stove is a saturatedhydrocarbon.

CH C HHHH

HCH H


Aromatic Hydrocarbons Mostaromatic compounds are based onbenzene, the compound repre-sented by the model in Figure 28.Look for this structure to helpidentify an aromatic hydrocar-bon. As the name implies, aro-matic hydrocarbons often havestrong odors and are thereforeused in such products as air fresh-eners and moth balls.

Other Organic CompoundsMany other types of organic compounds exist that have atomsof halogens, oxygen, sulfur, and phosphorus in their molecules.A few of these types of compounds and their uses are describedin the chart below.


CC

CC

CH

HH

H

HH

C

Figure 28 Benzene has a ring of sixcarbons with alternating double andsingle bonds. Benzene is the startingmaterial for manufacturing manyproducts, including medicines.

Type of compound Uses Examples

1. What is a hydrocarbon?

2. How many electrons are shared in a double bond? a triplebond?

3. Comparing Concepts Compare saturated and unsatu-rated hydrocarbons.

REVIEW

Types and Uses of Organic Compounds

Alkyl halides starting material for chloromethane (CH3Cl)Teflon bromoethane (C2H5Br)

refrigerant (freon)

Alcohols rubbing alcohol methanol (CH3OH)gasoline additive ethanol (C2H5OH)antifreeze

Organic acids food preservatives ethanoic acid (CH3COOH)flavorings propanoic acid (C2H5COOH)

Esters flavorings methyl ethanoate fragrances (CH3COOCH3)clothing (polyester) ethyl propanoate

(C2H5COOC2H5)

NSTA

TOPIC: Organic CompoundsGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP375


Chapter Highlights

Chapter 15390

SECTION 1 SECTION 2

Vocabularyionic compounds (p. 374)

covalent compounds (p. 375)

Section Notes

• Ionic compounds containionic bonds and are com-posed of oppositely chargedions arranged in a repeatingpattern called a crystal lattice.

• Ionic compounds tend to bebrittle, have high meltingpoints, and dissolve in waterto form solutions that con-duct an electric current.

• Covalent compounds arecomposed of elements thatare covalently bonded andconsist of independentparticles called molecules.

• Covalent compounds tend tohave low melting points. Mostdo not dissolve well in waterand do not form solutions thatconduct an electric current.

Vocabularyacid (p. 377)

base (p. 379)

pH (p. 380)

salt (p. 382)

Section Notes

• An acid is a compound thatincreases the number ofhydrogen ions in solution.Acids taste sour, turn bluelitmus paper red, react withmetals to produce hydrogengas, and react with limestoneor baking soda to producecarbon dioxide gas.

• A base is a compound thatincreases the number ofhydroxide ions in solution.Bases taste bitter, feel slip-pery, and turn red litmuspaper blue.

• When dissolved in water,every molecule of a strongacid or base breaks apart toform ions. Few molecules ofweak acids and bases breakapart to form ions.

• When combined, an acid anda base neutralize one anotherto produce water and a salt.

• pH is a measure of hydro-nium ion concentration in asolution. A pH of 7 indicatesa neutral substance. A pH ofless than 7 indicates anacidic substance. A pH ofgreater than 7 indicates abasic substance.

• A salt is an ionic compoundformed from the positive ionof a base and the negativeion of an acid.

LabsCabbage Patch Indicators (p. 688)

Making Salt (p. 690)

Skills CheckVisual UnderstandingLITMUS PAPER You can use the ability of acidsand bases to change the color of indicators toidentify a chemical as an acid or base. Litmusis an indicator commonly used in schools.Review Figures 8 and 10, which show how the color of litmus paper is changed by anacid and by a base.

pH SCALE Knowing whether a substance is an acid or abase can help explainsome of the properties ofthe substance. The pHscale shown in Figure13 illustrates the pHranges for manycommon substances.



TOPIC: Ionic Compounds sciLINKS NUMBER: HSTP355

TOPIC: Covalent Compounds sciLINKS NUMBER: HSTP360

TOPIC: Acids and Bases sciLINKS NUMBER: HSTP365

TOPIC: Salts sciLINKS NUMBER: HSTP370

TOPIC: Organic Compounds sciLINKS NUMBER: HSTP375



KEYWORD: HSTCMP

391Chemical Compounds

Vocabularyorganic compounds (p. 383)

biochemicals (p. 384)

carbohydrates (p. 384)

lipids (p. 385)

proteins (p. 386)

nucleic acids (p. 387)

hydrocarbons (p. 388)

Section Notes

• Organic compounds arecovalent compounds com-posed of carbon-basedmolecules.

• Each carbon atom forms fourbonds with other carbonatoms or with atoms of otherelements to form straightchains, branched chains, or rings.

• Biochemicals are organiccompounds made by livingthings.

• Carbohydrates are biochemicals that arecomposed of one or more simple sugars bonded together; they areused as a source of energyand for energy storage.

• Lipids are biochemicals thatdo not dissolve in water andhave many functions, includ-ing storing energy and mak-ing up cell membranes.

• Proteins are biochemicalsthat are composed of aminoacids and have many func-tions, including regulatingchemical activities, transport-ing and storing materials,and providing structuralsupport.

• Nucleic acids are biochemi-cals that store informationand help to build proteinsand other nucleic acids.

SECTION 3

• Hydrocarbons are organiccompounds composed ofonly carbon and hydrogen.

• In a saturated hydrocarbon,each carbon atom in themolecule shares a singlebond with each of four other atoms.

• In an unsaturated hydro-carbon, at least two carbonatoms share a double bondor a triple bond.

• Many aromatic hydrocarbonsare based on the six-carbonring of benzene.

• Other organic compounds,including alkyl halides, alco-hols, organic acids, andesters, are formed by addingatoms of other elements.




1. Compounds that have low melting pointsand do not usually dissolve well in waterare ? . (ionic compounds or covalentcompounds)

2. A(n) ? turns red litmus paper blue.(acid or base)

3. ? are composed of only carbon andhydrogen. (Ionic compounds orHydrocarbons)

4. A biochemical composed of amino acids isa ? . (lipid or protein)

5. A source of energy for living things can befound in ? . (nucleic acids orcarbohydrates)


Multiple Choice

6. Which of the following describes lipids?a. used to store energyb. do not dissolve in waterc. make up most of the cell membraned.all of the above

7. An acid reacts to produce carbon dioxidewhen the acid is added toa. water.b. limestone.c. salt.d. sodium

hydroxide.

8. Which of thefollowing does NOTdescribe ionic compounds?a. high melting pointb. brittlec. do not conduct electric currents in waterd.dissolve easily in water

9. An increase in the concentration ofhydronium ions in solution ? the pH.a. raisesb. lowersc. does not affectd.doubles

10. Which of the following compounds makesup the majority of cell membranes?a. lipidsb. ionic compoundsc. acidsd.nucleic acids

11. The compounds that store information forbuilding proteins area. lipids.b. hydrocarbons.c. nucleic acids.d.carbohydrates.

Short Answer

12. What type of compound would you useto neutralize a solution of potassiumhydroxide?

13. Explain why the reaction of an acid witha base is called neutralization.

14. What characteristic of carbon atoms helpsto explain the wide variety of organiccompounds?

15. Compare acids and bases based on the ionproduced when each compound is dis-solved in water.


Concept Mapping

16. Use the followingterms to create a con-cept map: acid, base,salt, neutral, pH.


17. Fish give off the base ammonia, NH3, aswaste. How does the release of ammoniaaffect the pH of the water in the aquar-ium? What can be done to correct theproblem?

18. Many insects, such as fire ants, injectformic acid, a weak acid, when they biteor sting. Describe the type of compoundthat should be used to treat the bite.

19. Organic compounds are also covalentcompounds. What properties would youexpect organic compounds to have as aresult?

20. Farmers often can taste their soil to deter-mine whether the soil has the correctacidity for their plants. How would tastehelp the farmer determine the acidity ofthe soil?

21. A diet that includes a high level of lipidsis unhealthy. Why is a diet containing nolipids also unhealthy?


Study the structural formulas below, and thenanswer the questions that follow.

22. A saturated hydrocarbon is represented bywhich structural formula(s)?

23. An unsaturated hydrocarbon is repre-sented by which structural formula(s)?

24. An aromatic hydrocarbon is representedby which structural formula(s)?


CC

CC

CH

HH

H

H

C

CH

HH CC

CC

C

HH H

H

HH

HH

H

H

H H

C

CHC HHH

CC HH

HHHCH

HH

a

c

b

HC

H

HC

H

HC

H

HC

H

d



ReadingCheck-up



Unique Compounds

394

What makes you unique? Would you believe it’sa complex pattern of information found on thedeoxyribonucleic acid (DNA) in your cells? Wellit is! And by analyzing how this information isarranged, scientists are finding clues abouthuman ancestry.

Mummy Knows BestIf you compare the DNA from an older speciesand a more recent species, you can tell whichtraits were passed on. To consider the questionof human evolution, scientists must use DNAfrom older humans—like mummies. Moleculararcheologists study DNA from mummies in orderto understand human evolution at a molecularlevel. Since well-preserved DNA fragments frommummies are scarce, you might be wonderingwhy some ancient DNA fragments have beenpreserved better than others.

Neutralizing AcidsThe condition of preserved DNA fragmentsdepends on how the mummy was preserved. Thetannic acid—commonly found in peat bogs—that isresponsible for preserving mummies destroysDNA. But if there are limestone rocks nearby, the

DNA from mummies like this one providesscientists with valuable information.

calcium carbonate from these rocks neutralizesthe tannic acid, thereby preserving the DNA.

Molecular PhotocopyingWhen scientists find well-preserved DNA, theymake copies of it by using a technique calledpolymerase chain reaction (PCR). PCR takesadvantage of polymerases to generate copies ofDNA fragments. Polymerases are found in allliving things, and their job is to make strands ofgenetic material using existing strands as tem-plates. That is why PCR is also called molecularphotocopying. But researchers who use thistechnique risk contaminating the ancient DNAwith their own DNA. If even one skin cell fallsinto the PCR mixture, the results are ruined.

Mysteries Solved?PCR has been used to research ancient civiliza-tions and peoples. For example, scientists foundan 8,000-year-old human brain in Florida. Thisbrain was preserved well enough for scientists toanalyze the DNA and to conclude that today’sNative Americans are not direct descendants ofthis group of people.

PCR has also been used to analyze the cultureof ancient peoples. When archeologists tested thepigments used in 4,000-year-old paintings onrocks along the Pecos River, in Texas, they foundDNA that was probably from bison. This was anunexpected discovery because there were nobison along the Pecos River when the paintingswere made. The archeologists have concluded,therefore, that the artists must have tried veryhard to find this specific pigment for their paint.This leads the archeologists to believe that thepaintings must have had some spiritual meaning.

On Your Own Research ways PCR is being used to detectdiseases and infections in humans and animals.


this protein even closer, it looks like tangledspaghetti. Scientists believe that this tangledpart makes the silk springy and a repeatingsequence of five amino acids makes the protein stretchy.

Spinning TailsScientists think they have identified the piece of DNA needed to make spider silk. Syntheticsilk can be made by copying a small part of thisDNA and inserting it into the bacteriumEscherichia coli. The bacteria read the gene andmake liquid silk protein. Biologists at theUniversity of Wyoming, in Laramie, have comeup with a way to spin spider silk into threadsby pushing the liquid protein through fine tubes.

What Do You Think? Scientists seem to think that there are manyuses for synthetic spider silk. Make a list in yourScienceLog of as many things as you can thinkof that this material would be good for.

395

T H E S E C R ETS O F S P I D E R S I L KWhat is as strong as steel, more elastic than arubber band, and able to stop a speeding bul-let? Spider silk! Spiders make this silk to weavetheir delicate but deadly webs.

The Tangled Web We WeaveIf you’ve seen a spider web, you’ve probablynoticed that it resembles a bicycle wheel. The“spokes” of the web are made of a silk threadcalled dragline silk. The sticky, stretchy part ofthe web is called capture silk because that’swhat spiders use to capture their prey. Spidersilk is made of proteins, and these proteins aremade of blocks of amino acids.

There are 20 naturally occurring aminoacids, but spider silk has only seven of them.Until recently, scientists knew what the silk ismade of, but they didn’t know how theseamino acids were distributed throughout theprotein chains.

Scientists used a technique called nuclearmagnetic resonance (NMR) to see the structureof dragline silk. The silk fiber is made of twotough strands of alanine–rich protein embed-ded in a glycine–rich substance. If you look at

A golden orb-weaving spider on its web

Spiders use organs called spinnerets tospin their webs. This image of spinneretswas taken with a scanning electronmicroscope.


396 Chapter 16

Radioactivity . . . . . . . . 398Geology Connection . . 399Environment

Connection . . . . . . . 402MathBreak . . . . . . . . . 404Internet Connect . . . . 405

Energy from the Nucleus . . . . . . . . 406

QuickLab . . . . . . . . . . 407Apply . . . . . . . . . . . . . 409AstronomyConnection . . . . . . . .410


Chapter Review . . . . . . . . . . 414


LabBook . . . . . . . . . . . 692–693

AtomicEnergyAtomicEnergy

Nuclear Detective AgentsLook closely at the blood vessel pathways that show up soclearly in this image of a human hand. Medical scientistssometimes inject radioactive substances into the body to helplocate tumors and measure the activity of certain organs.After radioactive emissions from the substance are measuredusing a scanning device, computers turn this data into animage. In this chapter, you will learn about the radioactiveenergy of some atoms, about nuclear energy as a powersource, and about other uses of radioactive materials.


1. What is nuclear radiation?2. How are radioactive

materials used?3. What are two concerns

about energy obtainedfrom nuclear reactions?


397

WATCH YOUR HEADSIUM!The nuclei of radioactive atoms areunstable. Therefore, they decay andchange into different nuclei. In thisactivity, you will model the decay ofunstable nuclei into stable nuclei.

Procedure1. Place 100 pennies

heads-up in a box with a lid.The pennies represent radioactive“headsium” nuclei. Record the 100headsium nuclei present as Trial 0in your ScienceLog.

2. Close the box, and shake it vigor-ously up and down for 5 seconds.

3. Open the box, and remove all ofthe “tailsium” nuclei, pennies thatare tails-up. These pennies repre-sent stable nuclei that result fromdecay. Count the number of head-sium nuclei remaining, and recordit in your ScienceLog as Trial 1.

4. Continue performing trials untilyou have no more pennies in thebox or you have finished five trials,whichever comes first. Record allyour results.

Analysis5. On a piece of graph paper, graph

your data by plotting “Number ofheadsium nuclei” on the y-axis and“Trial number” on the x-axis.

6. What trend do you see in the num-ber of headsium nuclei over time?

7. Compare your graph with thegraphs of other students in your class.

Atomic EnergyCopyright © by Holt, Rinehart and Winston. All rights reserved.


Section

1

nuclear radiation beta decayradioactivity isotopesradioactive decay gamma decayalpha decay half-lifemass number

Compare alpha, beta, andgamma decay.

Describe the penetrating powerof the three types of nuclearradiation.

Calculate ages of objects using half-life.

Identify uses of radioactive materials.

Chapter 16398

RadioactivityWhen scientists perform experiments, they don’t always getthe results they expect. In 1896, a French scientist namedHenri Becquerel did not get the results he expected, but hedid discover a fascinating new area of science.

Discovering RadioactivityBecquerel’s hypothesis was that fluorescent minerals couldgive off X rays. (Fluorescent materials glow when exposed tolight, as shown in Figure 1.) To test his hypothesis, Becquerelplaced a fluorescent mineral on top of a photographic platewrapped in paper. He placed the setup in bright sunlight.

Becquerel predicted that an image of the mineral wouldappear on the plate. After developing the plate,

he saw the image he expected.

An Unexpected Result Becquerel tried toconfirm his results, but cloudy weatherdelayed his plans. He placed his materials ina drawer. After several days, he developed theplate anyway. He was amazed to see a strongimage, shown in Figure 2.

Becquerel’s results showed that evenwithout light, the mineral gave off energythat passed through paper and made animage on the plate. After more tests,Becquerel concluded that this energy comesfrom uranium, an element in the mineral.

Naming the Unexpected Scientists callthis energy nuclear radiation, high-energyparticles and rays that are emitted by thenuclei of some atoms. Marie Curie, a sci-entist working with Becquerel, named theability of some elements to give off nuclearradiation radioactivity.

Figure 1 The brightly colored portions of thissample are fluorescent in ultraviolet light.

Figure 2 The blurry image on this photographicplate surprised Becquerel.


Alpha particles emitted during alphadecay eventually gain two electronsfrom nearby atoms and becomehelium atoms. Almost all of the he-lium in Earth’s atmosphere formedfrom alpha particles emitted bynuclei of radioactive atoms.


Nuclear Radiation Is Produced Through DecayRadioactive decay is the process in which the nucleus of aradioactive atom releases nuclear radiation. Three types ofradioactive decay are alpha decay, beta decay, and gamma decay.

Alpha Decay The release of an alpha particle from a nucleusis called alpha decay. An alpha particle consists of two protonsand two neutrons, so it has a mass number of 4 and a chargeof 2. An alpha particle is identical to the nucleus of a heliumatom. Many large radioactive nuclei give off alpha particles tobecome nuclei of atoms of different elements. One example isradium-226. (Remember that the number that follows the nameof an element indicates the mass number—the sum of the pro-tons and neutrons in an atom.)

Conservation in Decay Look at the model of alpha decayin Figure 3. This model illustrates two important features ofall types of radioactive decay. First, the mass number is con-served. The sum of the mass numbers of the starting ma-terials is always equal to the sum of the mass numbers ofthe products. Second, charge is conserved. The sum of thecharges of the starting materials is always equal to the sumof the charges of the products.

Atomic Energy 399

Figure 3 Alpha Decay of Radium-226

Mass number is conserved.226 222 4

Charge is conserved.(88) (86) (2)

Radium-226 Radon-222

Charge: 86

Charge: 88Charge: 2

Alpha particle(helium-4)

Energy


Beta Decay The release of a beta particle from a nucleus is called beta decay. A beta particle can be either an electron(having a charge of 1 and a mass of almost 0) or a positron(having a charge of 1 and a mass of almost 0). Because elec-trons and positrons do not contain protons or neutrons, themass number of a beta particle is 0.

Two Types of Beta Decay A carbon-14 nucleus undergoesbeta decay as shown in the model in Figure 4. During thisdecay, a neutron breaks into a proton and an electron. Noticethat the nucleus becomes a nucleus of a different element, andmass number and charge are conserved, similar to alpha decay.

Not all isotopes of an element decay in the same way.(Remember that isotopes are atoms that have the same num-ber of protons but different numbers of neutrons.) A carbon-11 nucleus undergoes beta decay when a proton breaksinto a positron and a neutron. However, the beta decay ofcarbon-11 still changes the nucleus into a nucleus of a differ-ent element while conserving both mass number and charge.

Gamma Decay Did you notice in Figures 3 and 4 that energyis released during alpha decay and beta decay? Some of thisenergy is in the form of gamma rays, a form of light with veryhigh energy. The release of gamma rays from a nucleus is calledgamma decay. Gamma decay occurs after alpha or beta decay asthe particles in the nucleus shift to a more stable arrangement.Because gamma rays have no mass or charge, gamma decay alonedoes not cause one element to change into another as do alphadecay and beta decay.

Chapter 16400

Alpha and beta decay resultin one element changing intoanother element, a processknown as transmutation.Scientists can performartificial transmutations bysmashing particles intonuclei at high speeds. Allelements with an atomicnumber greater than 94 werecreated through this process.

Self-CheckWhich type of nuclearradiation has thelargest mass number?(See page 724 to checkyour answer.)

Figure 4 Beta Decay of Carbon-14

Mass number is conserved.14 14 0

Charge is conserved.(6) (7) (1)

Carbon-14 Nitrogen-14

Beta particle(electron)

Energy

Charge: 6 Charge: 1–

Charge: 7


The Penetrating Power of RadiationThe three forms of nuclear radiation differ in their ability topenetrate (go through) matter. This difference is due to themass and charge associated with each type of radiation, as youcan see in Figure 5.

Effects of Radiation on Matter Nuclear radiation can“knock” electrons out of atoms and break chemical bondsbetween atoms. Both of these actions can cause damage to living and nonliving matter.

Damage to Living Matter When an organism absorbs radi-ation, its cells can be damaged, causing burns similar to thosecaused by touching a hot object. A single large exposure toradiation can lead to radiation sickness. Symptoms of this con-dition range from fatigue and loss of appetite to hair loss,destruction of blood cells, and even death. Exposure to radiation can also increase the risk of cancer because of thedamage done to cells.

Figure 5 The Penetrating Abilities of Nuclear Radiation

Atomic Energy 401

Marie and Irene Curie diedof leukemia, a type of can-cer in which abnormal whiteblood cells multiply andinterfere with the body’simmune system. It is thoughtthat exposure to radiationcaused their leukemia.

Paper Aluminum Concrete

Radioactivematerial

Alpha particles havethe greatest charge andmass. They travel about7 cm through air andare stopped by paperor clothing.

Beta particles have a 1– or 1+charge and almost no mass.They are more penetrating thanalpha particles. They travelabout 1 m through air, but arestopped by 3 mm of aluminum.

Gamma rays have no charge ormass and are the most pene-trating. They are blocked by verydense, thick materials, such as afew centimeters of lead or a fewmeters of concrete.

Alpha particles

Beta particles

Gamma rays


Radioactive radon-222 forms fromthe radioactive decay of uraniumfound in soil and rocks. Becauseradon is a gas, it can enter buildingsthrough gaps in the walls and floors.If radon is inhaled, the alpha parti-cles emitted through alpha decaycan damage sensitive lung tissue. Inaddition, solid polonium forms asradon decays. The polonium stays inthe lungs and emits more alpha par-ticles, greatly increasing the risk ofcancer. Radon detectors are availableto monitor radon levels in the home.


Damage to Nonliving Matter Radiation can also damagenonliving matter. When radiation knocks electrons out of metalatoms, the metal is weakened. The metal structures of build-ings, such as nuclear power plants, can become unsafe. Highlevels of radiation, such as gamma rays from the sun, can dam-age space vehicles.

Damage at Different Depths Because gamma rays are themost penetrating nuclear radiation, they can cause damagedeep within an object. Beta particles cause damage closer tothe surface, while alpha particles cause damage very near thesurface. However, if a source of alpha particles enters an organ-ism, alpha particles cause the most damage because they arethe largest and most massive radiation.

1. What is radioactivity?

2. What is meant by the phrase “mass number is conserved”?

3. Comparing Concepts Compare the penetrating power ofthe three types of nuclear radiation discussed.

Nuclei Decay to Become Stable You already know that a nucleus consists of protons and neu-trons together in a very small space. Protons have a positivecharge, so they repel one another. (Remember, opposite chargesattract, but like charges repel.) Why don’t the protons fly apart?Because of the strong force, an attractive force that holds theprotons and neutrons together in the nucleus.

Too Many Protons The strong force acts only atextremely short distances. As a result, a large nucleus,

as modeled in Figure 6, is often radioactive. In fact,all nuclei composed of more than 83 protons areradioactive. There are simply too many protons.Although some of these nuclei can exist for billionsof years before they decay, they do eventually decay

and are therefore called unstable.

REVIEW

Chapter 16402

Poloniumatomic number 84

Figure 6 This nucleus is unstable, or radioactive, because therepulsion between the protons overcomes the strong force.


Ratio of Neutrons to Protons A nucleus can also beunstable if it contains too many or too few neutronscompared with protons. Nuclei with more than 60 pro-tons are stable when the ratio of neutrons to protonsis about 3 to 2. Nuclei with fewer than 20 protons onlyneed a ratio of about 1 to 1 for stability. This explainsthe existence of small radioactive isotopes, like the onesmodeled in Figure 7.

How Does a Nucleus Become Stable? An unstablenucleus will emit (give off) nuclear radiation until ithas a stable number of neutrons and protons. An unsta-ble nucleus doesn’t always achieve stability throughone decay. In fact, some nuclei are just the first in aseries of radioactive isotopes formed as a result of alphaand beta decays. Eventually, a nonradioactive nucleusis formed. The nuclei of the most common isotope ofuranium, uranium-238, forms the nonradioactive nucleiof lead-206 after a series of 14 decays.

Finding a Date by DecayFinding a date for someone can bechallenging—especially if they are sev-eral thousand years old! When hikersin the Italian Alps found the remainsshown in Figure 8 in 1991, scientistswere able to estimate the time ofdeath—about 5,300 years ago! How didthey do this? The decay of radioactivecarbon was the key.

Carbon-14—It’s in You! Carbon atoms are found inall living things. A small percentage of these atoms areradioactive carbon-14 atoms. During an organism’s life,the percentage of carbon-14 in the organism stays aboutthe same because the atoms that decay are replaced byatoms taken in from the atmosphere by plants or fromfood by animals. But when an organism dies, thecarbon-14 is no longer replaced. Over time, the levelof carbon-14 in the remains drops through decay.

Figure 7 The ratio of neutrons toprotons in hydrogen-3 and beryllium-10is greater than 1 to 1. Therefore, thenuclei of these isotopes are unstable.

2 neutrons1 proton

Hydrogen-3

6 neutrons4 protons

Beryllium-10

Figure 8 The remains of the Iceman,a 5,300-year-old mummy, are the bestpreserved of a human from that time.

403Atomic Energy


Decay Occurs at a Steady Rate Scientists have determinedthat every 5,730 years, half of the carbon-14 in a sampledecays. The rate of decay is constant and is not affected byother conditions, such as temperature or pressure. Each radio-active isotope has its own rate of decay, called half-life. Ahalf-life is the amount of time it takes for one-half of thenuclei of a radioactive isotope to decay. Figure 9 is a model ofthis process. The table below lists some radioactive isotopeswith a wide range of half-lives.

Determining Age By measuring the number of decays eachminute, scientists determined that a little less than half of thecarbon-14 in the Iceman’s body had decayed. This means thatnot quite one complete half-life (5,730 years) had passed sincehe died. You can try your hand at determining ages with theMathBreak at left.

Carbon-14 can be used to determine the age of objects upto 50,000 years old. To calculate the age of older objects, otherelements must be used. For example, potassium-40, with ahalf-life of 1.3 billion years, is used to date dinosaur fossils.

Figure 9 Half of any radio-active sample decays duringeach half-life.

Chapter 16404

How Old Is It?An antler has one-fourth ofits original carbon-14unchanged. As shown inFigure 9, two half-lives haveoccurred. To determine theage of the antler, multiply thenumber of half-lives that havepassed by the length of ahalf-life. The antler’s age istwo times the half-life ofcarbon-14:

2 5,730 years 11,460 years

Now It’s Your TurnDetermine the age of a spearcontaining one-eighth its origi-nal amount of carbon-14.

MATH BREAK Examples of Half-lives

Isotope Half-life Isotope Half-life

Uranium-238 4.5 billion years Polonium-210 138 days

Oxygen-21 3.14 seconds Nitrogen-13 10 minutes

Hydrogen-3 12.3 years Calcium-36 0.1 second

The original samplecontains a certainamount of radio-active isotope.

After one half-life,one-half of the originalsample has decayed,leaving half unchanged.

After two half-lives,one-fourth of the original sample remains unchanged.

After three half-lives,only one-eighth ofthe original sampleremains unchanged.


Radioactivity and Your WorldAlthough radioactivity can be dangerous, it alsohas positive uses. Most medical and industrial usesinvolve small amounts of nuclei with very shorthalf-lives, so human exposure is low. Keep in mindthat there are risks involved, but often, the ben-efits outweigh the risks.

Uses of Radioactivity You have learned howradioactive isotopes are used to determine the ageof objects. Some isotopes can be used as tracers—radioactive elements whose paths can be followedthrough a process or reaction. Tracers help farmersdetermine how well plants take in elements fromfertilizers. Tracers also help doctors diagnose medi-cal problems, as shown in Figure 10. Radiation detec-tors are needed to locate the radioactive materialin the organism.

Radioactive isotopes can also help detect defectsin structures. For example, radiation is used to testthe thickness of metal sheets as they are made.Another structure-testing use of radioactive isotopesis shown in Figure 11. More uses of radioactive iso-topes are listed in the chart below.

Atomic Energy 405

REVIEW

Killing cancer cells Sterilizing food and

health-care products

Detecting smoke Powering space

probes

Figure 10This scan of athyroid was made usingradioactive iodine-131. The dark areashows the location of a tumor.

Figure 11 Engineers can find weak spotsin materials and leaks in pipes by detectinga tracer using a Geiger counter.

More Uses of Radioactive Isotopes

1. What is a half-life?

2. Give two examples each of how radioactivity is usefuland how it is harmful.

3. How many half-lives have passed if a sample containsone-eighth of its original amount of radioactive material?

4. Doing Calculations A rock contains one-fourth of its origi-nal amount of potassium-40. Calculate the rock’s age if thehalf-life of potassium-40 is 1.3 billion years.

NSTA

TOPIC: Discovering Radioactivity, Radioactive Isotopes


Section

2

nuclear fissionnuclear chain reactionnuclear fusion

Describe the process of nuclearfission.

Describe the process of nuclearfusion.

Identify advantages anddisadvantages of energy fromthe nucleus.

Chapter 16406

Energy from the NucleusFrom an early age, you were probably told not to play withfire. But fire itself is neither good nor bad, it simply has ben-efits and hazards. Likewise, getting energy from the nucleushas benefits and hazards. In this section you will learn abouttwo methods used to get energy from the nucleus—fission andfusion. Gaining an understanding of their advantages and dis-advantages is important for people who will make decisionsregarding the use of this energy—people like you!

Nuclear FissionNot all unstable nuclei decay by releasing an alpha or betaparticle or gamma rays. The nuclei of some atoms decay bybreaking into two smaller, more stable nuclei during a processcalled nuclear fission. Nuclear fission is the process in whicha large nucleus splits into two smaller nuclei with the releaseof energy.

The nuclei of uranium atoms, as well as the nuclei of otherlarge atoms, can undergo nuclear fission naturally. They canalso be made to undergo fission by hitting them with neu-trons, as shown by the model in Figure 12.

Figure 12 Fission of a Uranium-235 Nucleus

Uranium-235

Charge: 92

Charge: 36

Charge: 56

Charge: 0

Neutron

Charge: 0

Neutron

Charge: 0

Neutron

Charge: 0

Neutron

EnergyBarium-142

Krypton-91



Gone Fission

1. Make two paperballs from a sheetof paper.

2. Stand in a group, arm’slength apart, with yourclassmates.

3. Your teacher will gentlytoss one paper ball intothe group. If you aretouched by a ball, gentlytoss your paper balls intothe group.

4. Explain how this activity isa model of a chain reac-tion. Be sure to explainwhat the students and thepaper balls represent.

Energy from Matter Did you know that matter can bechanged into energy? It’s true! If you could determine the totalmass of the products in Figure 12 and compare it with thetotal mass of the reactants, you would find something strange.The products have a tiny bit less mass than the reactants. Whyare the masses different? Some of the matter was convertedinto energy.

The amount of energy released when a single ura-nium nucleus splits is not very great. But, keep in mindthat this energy comes from an incredibly tiny amountof matter—about one-fifth of the mass of a hydrogenatom, the smallest atom that exists. In Figure 13 you’llsee an example of how small amounts of matter can yieldlarge amounts of energy through nuclear fission.

Nuclear Chain Reactions Look at Figure 12 again. Sup-pose that two or three of the neutrons produced split otheruranium-235 nuclei, which released energy and some neutrons. And then suppose that two or three of those neu-trons split other nuclei, and so on. This situation is onetype of nuclear chain reaction—a continuous series of nuclearfission reactions. A model of an uncontrolled chain reac-tion is shown in Figure 14.

Atomic Energy 407

Figure 13 The nuclear fission ofthe uranium nuclei in one fuelpellet releases as much energy asthe chemical change of burningabout 1,000 kg of coal!

Uranium

Barium

Krypton

Neutron

Energy

Figure 14 A chain reaction results in the release of an enormousamount of energy.


Energy from a Chain Reaction In an uncontrolled chainreaction, huge amounts of energy are released very quickly. Infact, the tremendous energy of an atomic bomb is the resultof an uncontrolled chain reaction. In contrast, nuclear powerplants use controlled chain reactions. The energy released fromthe nuclei in the uranium fuel is used to generate electrical energy.Figure 15 shows how a nuclear power plant works.

Nuclear Versus Fossil Fuel Although nuclear power plantsare more expensive to build than power plants using fossil fuels,they are often less expensive to operate because less fuel is needed.Also, nuclear power plants do not release gases, such as carbondioxide, into the atmosphere. The use of fission extends our sup-ply of fossil fuels. However, the supply of uranium is limited.Many nations rely on nuclear power to supply their energyneeds. Nuclear power plants provide about 20 percent of theelectrical energy used in the United States.

The generator convertsthe kinetic energy ofthe spinning turbineinto electrical energy.

The steam turns aturbine attachedto a generator.

Figure 15 How a Nuclear Power Plant Works

Uranium-235 nuclei inthe fuel rods (blue)undergo a nuclearchain reaction. Controlrods (gray) absorbneutrons to keep thechain reaction at asafe level.

Energy from the chainreaction is absorbed bya coolant, often water.

Water turns to steamas it absorbs energyfrom the hot coolant.

Chapter 16408

They all fall down—but not at the samerate. Experimentwith models ofnuclear chain reac-tions on page 692 of the LabBook.

To cooling tower

1 2

3

4 5


Accidents Can Happen Withthe advantages described, whyis fission not more widely used?Well, there are risks involvedwith generating electrical energyfrom fission. Probably the mostimmediate concern is the pos-sibility of an accident. This fearwas realized in Chernobyl,Ukraine, on April 26, 1986, asshown in Figure 16. An explo-sion released large amounts ofradioactive uranium fuel andwaste products into the atmos-phere. The cloud of radioactivematerial spread over most ofEurope and Asia and evenreached as far as North America.

What Waste! Another concern is nuclear waste, includingused fuel rods, chemicals used to process uranium, and evenshoe covers and overalls worn by workers. Although artificialfission has been carried out for only about 50 years, the wastewill give off high levels of radiation for thousands of years.The rate of radioactive decay cannot be changed, so the wastemust be stored until it becomes less radioactive. Most of theused fuel rods are stored in huge vats of water. Some of theliquid wastes are stored in underground tanks. However, sci-entists continue to look for more long-term storage solutions.

Atomic Energy 409

What would you say if anuclear waste storage facilitywas planned near your town?Read about the debate over

Yucca Mountain on page 416.

Figure 16 During a test at the Chernobyl nuclear power plant, the emergency protection system was turned off. The reactor overheated, resulting in an explosion.

Storage Site Selection

A law that passed in 1987 requires the United Statesgovernment to build a large underground storagefacility to store nuclear waste. Imagine that you are ascientist in charge of finding a location for the site.Describe the characteristics of a good location. Keepin mind that the waste will need to be stored for avery long time without escaping into the environment.


Nuclear Fusion Fusion is another nuclear reaction in which matter is con-verted into energy. In the process of nuclear fusion, two ormore nuclei with small masses join together, or fuse, to forma larger, more massive nucleus.

In order for fusion to occur, the repulsion between posi-tively charged nuclei must be overcome. That requires unbe-lievably high temperatures—over 100,000,000C! But youalready know a place where such temperatures are reached—the sun. In the sun’s core, hydrogen nuclei fuse to form ahelium nucleus, as shown in the model in Figure 17.

Energy from Fusion? Energy foryour home cannot yet be generatedusing nuclear fusion. First, incred-ibly high temperatures are needed.At these temperatures, hydrogen isa plasma, the state of matter inwhich electrons have been removedfrom atoms. No material on Earthcan hold this plasma—imagine try-ing to bottle up plasma from thesun! Figure 18 shows equipmentused by researchers to try to con-tain plasma. Second, more energyis needed to create and contain theplasma than is produced by fusion.In spite of these problems, scien-tists predict that fusion will be usedto provide electrical energy—pos-sibly in your lifetime!

Figure 18 Electric current in large coils of wire produces astrong magnetic field that can contain plasma.

Hydrogen-1

Charge: 1 Charge: 1

Charge: 1 Charge: 1 Charge: 2

Hydrogen-1

Energy

Helium-4 Beta particle(positron)

Charge: 1

Beta particle(positron)

Charge: 1

Hydrogen-1 Hydrogen-1

Figure 17 The energy thatsustains life on Earth isproduced from fusion.


Hydrogen is not the only fuel starsuse for fusion. As a star gets older,its supply of hydrogen runs low andit begins to fuse larger atoms, suchas helium, carbon, and silicon.

Chapter 16410


Figure 19 The energy gen-erated by the fusion of thehydrogen-2 in 3.8 L (1 gal)of water would be about thesame amount of energygenerated by the chemicalchange of burning 1,140 L(300 gal) of gasoline!

Oceans of Fuel Unlike nuclearfission, there is little concern aboutrunning out of fuel for nuclearfusion. Although the hydrogen-2and hydrogen-3 isotopes used asfuel are much less common thanhydrogen-1, there is still enoughhydrogen in the waters of oceans andlakes to provide fuel for millions ofyears. In addition, a fusion reactionreleases more energy than a fissionreaction per gram of fuel, allowingfor even greater savings of otherresources, as shown in Figure 19.

Less Accident Prone The concernover an accident such as the one atChernobyl is much lower for fusion reactors. If an explosionoccurred, there would be very little release of radioactive ma-terials. The radioactive hydrogen-3 used for fuel in experi-mental fusion reactors is much less radioactive than theuranium fuel used in fission reactors.

Less Waste In addition to the advantages mentioned above,the products of fusion reactions are not radioactive, so therewould be much less radioactive waste to worry about. Thiswould make fusion an even “cleaner” source of energy thanfission. While fusion has many benefits over fission as anenergy source, large amounts of money will be required topay for the research to make fusion possible.

Atomic Energy 411

REVIEW

1. Which nuclear reaction is currently used to generate electrical energy?

2. Which nuclear reaction is the source of the sun’s energy?

3. What particle is needed to begin a nuclear chain reaction?

4. In both fission and fusion, what is converted into energy?

5. Comparing Concepts Compare the processes of nuclearfission and nuclear fusion.

NSTA

TOPIC: Nuclear Fission, Nuclear FusionGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP390, HSTP400

Chapter Highlights

Chapter 16412

SECTION 1

Vocabularynuclear radiation (p. 398)

radioactivity (p. 398)

radioactive decay (p. 399)

alpha decay (p. 399)

mass number (p. 399)

beta decay (p. 400)

isotopes (p. 400)

gamma decay (p. 400)

half-life (p. 404)

Section Notes

• Radioactive nuclei give offnuclear radiation in the formof alpha particles, beta parti-cles, and gamma raysthrough a process calledradioactive decay.

• During alpha decay, an alphaparticle is released from thenucleus. An alpha particle iscomposed of two protonsand two neutrons.

• During beta decay, a betaparticle is released from thenucleus. A beta particle canbe an electron or a positron.

• Gamma decay occurs withalpha decay and beta decaywhen particles in the nucleusrearrange and emit energy inthe form of gamma rays.

• Gamma rays penetratematter better than alpha orbeta particles. Beta particlespenetrate matter better thanalpha particles.

• Nuclear radiation can dam-age living and nonlivingmatter.

• Half-life is the amount oftime it takes for one-half ofthe nuclei of a radioactiveisotope to decay. The age ofsome objects can be deter-mined using half-lives.

• Uses of radioactive materialsinclude detecting defects inmaterials, sterilizing prod-ucts, tracing a plant’s or ani-mal’s use of an element,diagnosing illness, and pro-ducing electrical energy.

Skills CheckMath ConceptsHALF-LIFE Radioactive decay occurs at a steadyrate. To calculate the time that has passed, mul-tiply the number of half-lives by the length of ahalf-life. For example, a radioactive isotope hasa half-life of 10 days. If one-eighth of the origi-nal sample remains, then three half-lives havepassed. The time that has passed is:

3 10 days 30 days

Visual UnderstandingFISSION VERSUS FUSION The changes thatoccur in nuclear fission and nuclear fusion arevery different. Review Figure 12 on page 406and Figure 17 on page 410 to better understandthe starting materials, products, and processinvolved in fission and fusion.



TOPIC: Discovering Radioactivity sciLINKS NUMBER: HSTP380

TOPIC: Radioactive Isotopes sciLINKS NUMBER: HSTP385

TOPIC: Nuclear Fission sciLINKS NUMBER: HSTP390

TOPIC: Nuclear Reactors sciLINKS NUMBER: HSTP395

TOPIC: Nuclear Fusion sciLINKS NUMBER: HSTP400



KEYWORD: HSTRAD

413Atomic Energy

SECTION 2

Vocabularynuclear fission (p. 406)

nuclear chain reaction (p. 407)

nuclear fusion (p. 410)

Section Notes

• Nuclear fission occurs whena massive, unstable nucleusbreaks into two less massivenuclei. Nuclear fission is usedin power plants to generateelectrical energy.

• Nuclear fusion occurs whentwo or more nuclei combineto form a larger nucleus. Thesun’s energy comes from thefusion of hydrogen to formhelium.

• The energy released bynuclear fission and nuclearfusion is produced whenmatter is converted intoenergy.

• Nuclear power plants usenuclear fission to supplymany homes with electricalenergy without releasing car-bon dioxide or other gasesinto the atmosphere. Alimited fuel supply, radioac-tive waste products, and thepossible release of radioactivematerial are disadvantages offission.

• Fuel for nuclear fusion isplentiful, and only smallamounts of radioactive wasteproducts are produced.Fusion is not currently a prac-tical energy source because ofthe large amount of energyneeded to heat and containthe hydrogen plasma.

LabsDomino Chain Reactions (p. 692)



The statements below are false. For each state-ment, replace the underlined term to make atrue statement.

1. Nuclear fusion involves splitting anucleus.

2. During one beta decay, half of a radioac-tive sample will decay.

3. Nuclear fission includes the particles andrays released by radioactive nuclei.

4. Alpha decay occurs during the rearrange-ment of protons and neutrons in thenucleus.


Multiple Choice

5. Which of the following is a use ofradioactive material?a. detecting smokeb. locating defects in materialsc. generating electrical energyd. all of the above

6. Which particle both begins and is pro-duced by a nuclear chain reaction?a. positronb. neutronc. alpha particled. beta particle

7. Nuclear radiation that can be stopped bypaper is calleda. alpha particles. c. gamma rays.b. beta particles. d. None of the above

8. The half-life of a radioactive atom is 2 months. If you start with 1g of theelement, how much will remain after 6 months?a. One-half of a gram will remain.b. One-fourth of a gram will remain.c. One-eighth of a gram will remain.d. None will remain.

9. The waste products of nuclear fissiona. are harmless.b. are safe after 20 years.c. can be destroyed by burning them.d. remain radioactive for thousands of

years.

10. Which statement about nuclear fusion isfalse?a. Nuclear fusion occurs in the sun.b. Nuclear fusion is the joining of the

nuclei of atoms.c. Nuclear fusion is currently used to

generate electrical energy.d. Nuclear fusion uses hydrogen as fuel.

Short Answer

11. What conditions could cause a nucleus tobe unstable?

12. What are two dangers associated withnuclear fission?

13. What are two of the problems that needto be solved in order to make nuclearfusion a practical energy source?

14. In fission, the products have less massthan the starting materials. Explain whathappened.


Concept Mapping

15. Use the followingterms to create a con-cept map: radioactivedecay, alpha particle,beta particle, gammaray, nuclear radiation.


16. Smoke detectors often use americium-243to detect smoke particles in the air.Americium-243 undergoes alpha decay.Do you think that these smoke detectorsare safe to have in your home if usedproperly? Explain. (Hint: How penetratingare alpha particles?)

17. Explain how radiation can cause cancer.

18. Explain why nuclei of carbon, oxygen,and even iron can be found in stars.

19. If you could block all radiation fromsources outside your body, explain whyyou would still be exposed to some radiation.

MATH IN SCIENCE

20. A scientist used 10 g of phosphorus-32 in a test on plant growth but forgot torecord the date. When he measured thephosphorus-32 some time later, he foundonly 2.5 g remaining. If the half-life is 14days, how many days ago did he start theexperiment?


21. Use the graph to answer the questionsbelow:

a. What is the half-life of fermium-256? offermium-251?

b. Which of these isotopes is more stable?Explain.

22. The image of a small purse, shown below,was made in a similar manner asBecquerel’s original experiment. What con-clusions can be drawn about the penetrat-ing power of radiation from this image?

Atomic Energy 415

Time (hours)

Fermium-251

Fermium-256

Amou

nt o

f iso

tope

(gr

ams)

0

102030405060708090

100

1 2 3 4 5 6 7 8 9 10 11



ReadingCheck-up


SCIENTIFICDEBATE

Wasting Yucca Mountain?

416

SCIENTIFICDEBATE

I solated, unspoiled,quiet . . . a small moun-tain in Nevada called

Yucca Mountain seems like aperfect spot for a long hike—orperhaps a nuclear waste site!Yucca Mountain has been cho-sen as the nation’s first storagesite for high-level radioactivewaste. The plan is to seal77,000 tons of radioactivewaste in steel canisters andstore them in a maze ofunderground tunnels.

Construction of the facilityhas already begun—YuccaMountain is scheduled toreceive its first shipment ofnuclear waste by 2010. But the debate continues about

whether it would be safer tostore radioactive waste at YuccaMountain or to keep it where itis now—in temporary storagefacilities at various nuclearpower plants.

Pros and ConsThose who support construc-tion of the Yucca Mountainfacility point out that there aretwo major advantages to theplan. First, Yucca Mountain isfar from any densely populatedareas. Second, the climate isextremely dry. A dry climatemeans that rainfall is unlikelyto cause the water table to riseand come in contact with thestored radioactive waste.

Many opponents fear thatthe highly toxic waste couldeventually leak and contami-nate the water in wells, springs,and streams. In time, the

contamination could spread far-ther from the site and into thebiosphere. The biosphere is thelayer above and below the sur-face of the earth that supportslife.

In addition, some scientificreports suggest that it is possi-ble that the current dry climatecould change over thousandsof years into a rainy one, andthe water table could rise dra-matically.

Nevada residents argue thattheir economy is booming andthey don't particularly need the construction jobs the facil-ity would bring. Also theireconomy depends heavily ontourism, and residents worrythat fears about Nevada beinga dangerous place could causethe tourists to stay away.

Today construction at theYucca Mountain facility contin-ues. And existing storage sitesexpand with the waste gener-ated by nuclear power plants.So, where should the waste go?

Have Waste, Will Travel What do you think? Jotdown your initial thoughts.Then do research to find outwhether any of the proposedroutes from nuclear powerplants to Yucca Mountain arenear your town. Do your find-ings change your opinion? Whyor why not?

Supporters of the YuccaMountain storage facilitythink that this isolatedspot in Nevada is a suit-able place for permanentnuclear-waste disposal.Opponents of the sitedisagree.

Spent fuel rods are storedunderwater at a nuclearpower plant.


417

T he damage to stainless steel is caused mainly by neutronand heavy ion radiation inside nuclear reactors. The radiation

causes stress in the metal, which leads to corrosion and finally tocracking. Clearly this is not a desirable feature in parts of a nuclearreactor! Atzmon’s goal is to try to understand how to make themetal more corrosion resistant. He also hopes that by studying theway radiation affects the atoms of metals, he can find a way touse the incoming radiation to make the surface stronger.

Training the TeamA large part of Atzmon’s job is to train graduate students to assisthim with his research. He happily reports that these creative newscientists “absolutely contribute” to the development of novelapproaches. One interesting proposal is to use radiation effects tocreate crystal structures different from those that exist in nature.This could lead to the invention of new types of semiconductors,which are useful in modern electronic devices.

Always an Explorer Atzmon spends time sharing ideas with other materials scientists.He also teaches at the University of Michigan. This very busy manrecalls that as a young boy he became interested in experiment-ing with things to see how they work. He chose to play with toysthat encouraged his exploration. This curiosity has remained withhim and has been helpful in his profession.

Have you noticed that yourforks, knives, and spoonsdon’t tarnish easily? Mostmetal flatware is made ofstainless steel. Because itdoesn’t tarnish easily, stainlesssteel is also used in nuclearreactors. Dr. Michael Atzmonstudies radiation’s effects onmetals and other substances.He has a special interest inradiation’s effect on stainlesssteel. He hopes that by under-standing the changes thatoccur, scientists can preventfuture radiation defects.

M AT E R I A L S S C I E N T I S T

Advice to Young PeopleAtzmon believes that students shouldchoose to study a field that gives themthe deepest background. This opens upmany career opportunities and allows stu-dents to pursue what they eventually findinteresting. Most important, he adds,“People should do what they love doing!”

Understanding materialstructures can help in thedevelopment of better semi-conductors for microchips.


T I M E L I N E

U N I T Electricity

Unit 6418

61752

Benjamin Franklinflies a kite with a

key attached to it ina thunderstorm todemonstrate thatlightning is a form

of electricity.

1911Superconductivity is discovered.

Superconductivity is the ability that some metals and alloys have under certain conditions to carry electric

current without resistance.

1945Grace Murray Hopper,

a pioneer in computers andcomputer languages, coins theterm “debugging the computer”

after removing from the wiring ofher computer a moth that caused

the computer to fail.

1948The transistor is invented.

1961The invention of the

integrated circuit, whichuses millions of

transistors, revolutionizeselectronic technology.

an you imagine aworld without

computers, motors, oreven light bulbs? Yourlife would be very dif-ferent indeed withoutelectricity and thedevices that dependon it. In this unit, youwill learn how electric-ity results from tinycharged particles, howelectricity and magnet-ism interact, and howelectronic technologyhas revolutionized theworld in a relativelyshort amount of time.This timeline includessome of the eventsleading to our currentunderstanding of elec-tricity, electromagnet-ism, and electronictechnology.

C


1773American colonists holdthe “Boston Tea Party”and dump 342 chests

of British tea intoBoston Harbor.

1831British scientist Michael Faraday and

American physicist Joseph Henryseparately demonstrate the

principle of electromagnetic induction(using magnetism to generate electricity).

1876The telephone is officially invented

by Alexander Graham Bell, whobeats Elisha Gray to the patent

office by only a few hours.

1902Dutch physician Willem Einthovendevelops the first electrocardio-

graph machine to record the tinyelectric currents that pass through

the body’s tissues.

1985The first portable CD player

is introduced.

Garry Kasparov, reigning world chess champion,

loses a historic match to a computernamed Deep Blue.

1974The first commercially

successful microprocessorchip is introduced.

419Electricity

1997


420 Chapter 17

Electric Charge and Static Electricity . . . . . . 422


Electrical Energy . . . . . 430Internet Connect . . . 432

Electric Current . . . . . . 433Biology Connection . . .435MathBreak . . . . . . . . .437Apply . . . . . . . . . . . . 439Internet Connect . . . 439

Electric Circuits . . . . . . 440Biology Connection . . 441QuickLabs . . . . . 442, 443Internet Connect . . . 445

Chapter Review . . . . . . . . . . . 448


LabBook . . . . . . . . . . . 694–697

Introduction to ElectricityIntroduction to Electricity

It’s shocking!This eighth-grader is having fun learning firsthand aboutstatic electricity. She is touching a Van de Graaf generator,a device that produces positive electrical charges on themetal globe. These positive charges move through her bodyto the strands of hair on her head. Like charges repel eachother, so each strand of her hair repels all the other hairs.In this chapter, you’ll learn more about static electricityand how you use electrical energy in your everyday life.


1. What is static electricity,and how is it formed?

2. How is electrical energyproduced?

3. What is a circuit, andwhat parts make up a circuit?


421

CHARGE OVER MATTERIn this activity, you will make anelectrically charged object and use it to pick up other objects.

Procedure

1. Cut 6–8 small squares of tissuepaper. Each square should beabout 2 cm 2 cm. Place thesquares on your desk.

2. Hold a plastic comb close to thepaper squares. Record what, ifanything, happens.

3. Now rub the comb with a piece ofsilk cloth for about 30 seconds.

4. Hold the comb close to the tissue-paper squares, but don’t touchthem. Record your observations. If nothing happens, rub the combfor a little while longer and tryagain.

Analysis

5. When you rubbed the comb withthe cloth, you gave the comb anegative electric charge. Why doyou think this charge allowed you to pick up tissue-papersquares?

6. What other objects do you thinkyou can use to pick up tissue-paper squares?

Introduction to ElectricityCopyright © by Holt, Rinehart and Winston. All rights reserved.


Figure 1 Protons and neutronsmake up the nucleus, which isthe center of the atom. Electronsare found outside the nucleus.

Chapter 17422

Electric Charge and Static ElectricityHave you ever reached out toopen a door and received ashock from the knob? You may have been surprised, andyour finger or hand probablyfelt tingly afterward. On drydays, you can easily produceshocks by shuffling your feeton a carpet and then lightlytouching a metal object. Theseshocks are a result of a buildupof static electricity. But what is static electricity, and how isit formed? To answer thesequestions, you need to learnabout charge.

Atoms and ChargeTo investigate charge, you must know a little about the natureof matter. All matter is composed of very small particles calledatoms. Atoms are made of even smaller particles called pro-tons, neutrons, and electrons, as shown in Figure 1. One impor-tant difference between protons, neutrons, and electrons isthat protons and electrons are charged particles and neutronsare not.

ElectronProton

Neutron

Section

1

law of electric conductorcharges insulator

electric force static electricityconduction electric dischargeinduction

State and give examples of thelaw of electric charges.

Describe three ways an objectcan become charged.

Compare conductors withinsulators.

Give examples of static electricityand electric discharge.

Charges Can Exert Forces Charge is a physical property thatis best understood by describing how charged objects interactwith each other. A charged object exerts a force—a push or apull—on other charged objects. There are two types of charge—positive and negative. The force between two charged objectsvaries depending on whether the objects have the same typeof charge or opposite charges, as shown in Figure 2. The chargedballs in Figure 2 illustrate the law of electric charges, whichstates that like charges repel and opposite charges attract.

Protons are positively charged, and electrons are negativelycharged. Because protons and electrons are oppositely charged,protons and electrons are attracted to each other. If this attrac-tion didn’t exist, electrons would fly away from the nucleusof an atom.

The Electric Force and the Electric Field The force between charged objects is an electric force. The strength of the electric force is determined by two factors. One factor isthe size of the charges. The greater the charges are, the greaterthe electric force. The other factor that determines the strengthof the electric force is the distance between the charges. Thecloser together the charges are, the greater the electric force.

The electric force exists because charged particles haveelectric fields around them. An electric field is a region arounda charged particle that can exert a force on another chargedparticle. If a charged particle is in the electric field of anothercharged particle, the first particle is attracted or repelled bythe electric force exerted on it.

Figure 2 The law of electriccharges states that like chargesrepel and opposite charges attract.

Introduction to Electricity 423Copyright © by Holt, Rinehart and Winston. All rights reserved.

+

+ +

–

– –

Objects that have oppo-site charges are attractedto each other, and theforce between the objectspulls them together.

Car manufacturers takeadvantage of the law ofelectric charges when paint-ing cars. The car bodies aregiven a positive charge.Then the paint droplets aregiven a negative charge asthey exit the spray gun. Thenegatively charged paintdroplets are attracted to thepositively charged car body,so most of the paint dropletshit the car body and lesspaint is wasted.

Objects that have the same charge arerepelled, and the forcebetween the objectspushes them apart.

Charge It! Although an atom contains charged particles, the atom itselfdoes not have a charge. Atoms contain an equal number ofprotons and electrons. Therefore, the positive and negativecharges cancel each other out, and the atom has no overallcharge. If the atoms of an object have no charge, how can theobject become charged? Objects become charged because theatoms in the objects can gain or lose electrons. If the atomsof an object lose electrons, the object becomes positivelycharged. If the atoms gain electrons, the object becomes nega-tively charged. There are three common ways for an object tobecome charged—friction, conduction, and induction. Whenan object is charged by any method, no charges are createdor destroyed. The charge on any object can be detected by adevice called an electroscope.

Friction Rubbing two objects together can cause electrons tobe “wiped” from one object and transferred to the other. If yourub a plastic ruler with a cloth, electrons are transferred fromthe cloth to the ruler. Because the ruler gains electrons, theruler becomes negatively charged. Conversely, because the clothloses electrons, the cloth becomes positively charged. Figure 3shows a fun example of objects becoming charged by friction.

Figure 3 When you rub a balloon against your hair,electrons from your hair are transferred to the balloon.


After the electrons are transferred,the balloon is negatively chargedand your hair is positively charged.

Your hair and the balloon areattracted to each other becausethey are oppositely charged.


Conduction Charging by conduction occurswhen electrons are transferred from oneobject to another by direct contact. For exam-ple, if you touch an uncharged piece of metalwith a positively charged glass rod, electronsfrom the metal will move to the glass rod.Because the metal loses electrons, it becomespositively charged. Figure 4 shows what hap-pens when you touch a negatively chargedobject to an uncharged object.

Induction Charging by induction occurs when charges in anuncharged object are rearranged without direct contact witha charged object. For example, when a positively charged objectis near a neutral object, the electrons in the neutral object areattracted to the positively charged object and move toward it.This movement produces a region of negative charge on theneutral object. Figure 5 shows what happens when you holda negatively charged balloon close to a neutral wall.

Conservation of Charge When you charge objects by anymethod, no charges are created or destroyed. Electrons simplymove from one atom to another, producing objects or regionswith different charges. If you could count all the protons andall the electrons of all the atoms before and after charging anobject, you would find that the numbers of protons and elec-trons do not change. Because charges are not created ordestroyed, charge is said to be conserved.

Introduction to Electricity 425

Movement of electrons

Figure 4 Touching a negativelycharged plastic ruler to anuncharged metal rod causes theelectrons in the ruler to travel tothe rod. The rod becomes nega-tively charged by conduction.

Figure 5 A negatively charged ballooninduces a positive charge on a smallsection of a wall because the electrons inthe wall are repelled and move away fromthe balloon.

Self-CheckPlastic wrap clings tofood containers because the wrap has a charge. Explain howplastic wrap becomescharged. (See page 724to check your answer.)


Detecting Charge To determine if an object has a charge, youcan use a device called an electroscope. An electroscope is a glassflask that contains a metal rod inserted through a rubber stop-per. There are two metal leaves at the bottom of the rod. Theleaves hang straight down when the electroscope is not chargedbut spread apart when it is charged, as shown in Figure 6.

Moving ChargesHave you ever noticed that the cords that connect electricaldevices to outlets are always covered in plastic, while the prongsthat fit into the socket are always metal? Both plastic and metalare used to make electrical cords because they differ in theirability to transmit charges. In fact, most materials can be dividedinto two groups based on how easily charges travel through thematerial. The two groups are conductors and insulators.

1. Describe how an object is charged by friction.

2. Compare charging by conduction and induction.

3. Inferring Conclusions Suppose you are conducting experi-ments using an electroscope. You touch an object to thetop of the electroscope, the metal leaves spread apart,and you determine that the object has a charge. However,you cannot determine the type of charge (positive or neg-ative) the object has. Explain why not.

REVIEW

426 Chapter 17

Electrons from a negativelycharged plastic ruler moveto the electroscope andtravel down the rod. Themetal leaves becomenegatively charged andspread apart.

Figure 6 When an electroscope ischarged, the metal leaves have thesame charge and repel each other.

A positively charged glassrod attracts the electrons in the metal rod, causingthe electrons to travel upthe rod. The metal leavesbecome positively chargedand spread apart.

Conductors A conductor is a material in which charges canmove easily. Most metals are good conductors because someof the electrons in metals are free to move about. Copper,silver, aluminum, and mercury are good conductors.

Conductors are used to make wires and other objects thattransmit charges. For example, the prongs on a lamp’s cordare made of metal so that charges can move in the cord andtransfer energy to light the lamp.

Not all conductors are metal. Household, or “tap,”water conducts charges very well. Because tapwater is a conductor, you can receive anelectric shock from charges traveling init. Therefore, you should avoid usingelectrical devices (such as the one inFigure 7) near water unless they arespecially designed to be waterproof.

Insulators An insulator is a material in which charges can-not easily move. Insulators do not conduct charges very wellbecause electrons are tightly bound to the atoms of the insu-lator and cannot flow freely. Plastic, rubber, glass, wood, andair are all good insulators.

Wires used to conduct electric charges are usually coveredwith an insulating material. The insulator prevents chargesfrom leaving the wire and protects you from electric shock.

Static ElectricityAfter taking your clothes out of the dryer, yousometimes find clothing stuck together. When thishappens, you might say that the clothes stick togetherbecause of static electricity. Static electricity is thebuildup of electric charges on an object.

When something is static, it is not moving. Thecharges that create static electricity do not move awayfrom the object they are stuck to. Therefore, the objectremains charged. For example, your clothes are chargedby friction as they rub against each other inside adryer. Positive charges build up on some clothes, andnegative charges build up on other clothes. Becauseclothing is an insulator, the charges stay on each pieceof clothing, creating static electricity. You can see theresult of static electricity in Figure 8.

Figure 8 Opposite charges on pieces of clothing are caused by static electricity. The clothes stick togetherbecause their charges attract each other.

Figure 7 Because tap water isa conductor, this hair dryer hasa label that warns people notto use it near water.



Electric Discharge Charges that build up as static electricityon an object eventually leave the object. The loss of static elec-tricity as charges move off an object is called electric discharge.Sometimes electric discharge occurs slowly. For example, clothesstuck together by static electricity will eventually separate ontheir own because their electric charges are transferred to watermolecules in the air over time.

Sometimes electric discharge occurs quickly and may beaccompanied by a flash of light, a shock, or a cracking noise.For example, when you walk on a carpet with rubber-soledshoes, negative charges build up in your body. When youtouch a metal doorknob, the negative charges in your bodymove quickly to the doorknob. Because the electric dischargehappens quickly, you feel a shock.

LightningOne of the most dramatic examples of electric discharge islightning. Benjamin Franklin was the first to discover that light-ning is a form of electricity. During a thunderstorm, Franklinflew a kite connected to a wire and successfully stored chargefrom a bolt of lightning. How does lightning form from abuildup of static electricity? Figure 9 shows the answer.

Chapter 17428

Although 70–80 percent ofpeople struck by lightningsurvive, many suffer fromlong-term side effects suchas memory loss, dizziness,and sleep disorders.

Figure 9 How Lightning Forms

a

b

c

During a thunderstorm, water dropletsand air move within the storm cloud.As a result, negative charges build upat the bottom of the cloud andpositive charges build up at the top.

Because different parts ofclouds have different charges,lightning can also occurwithin and between clouds.

The negative charge at the bottom of thecloud induces a positive charge on theground. The large charge difference causesa rapid electric discharge—called lightning.


Lightning Rods Benjamin Franklin also invented the light-ning rod. A lightning rod is a pointed rod connected to theground by a wire. Lightning usually strikes the highest pointin a charged area because that point provides the easiest pathfor the charges to reach the ground. Therefore, lightning rodsare always mounted so that they “stick out” and are the tallestpoint on a building, as shown in Figure 10.

Objects, such as a lightning rod, that are in contact withthe Earth are grounded. Any object that is grounded providesa path for electric charges to travel tothe Earth. Because the Earth is so large,it can give up or absorb electric chargeswithout being damaged. When light-ning strikes a lightning rod, the electriccharges are carried safely to the Earththrough the rod’s wire. By directing thelightning’s charge to the Earth, light-ning rods prevent lightning damage tobuildings.

Lightning Dangers Anything that sticksout in an area can provide a path forlightning. Trees and people in open areasare at risk of being struck by lightning.This is why it is particularly dangerousto be at the beach or on a golf courseduring a lightning storm. And standingunder a tree during a storm is danger-ous because the charge from lightningstriking a tree can jump to your body.


1. What is static electricity? Give an example of staticelectricity.

2. How is the shock you receive from a metal doorknobsimilar to a bolt of lightning?

3. Applying Concepts When you use an electroscope, youtouch a charged object to a metal rod that is held in placeby a rubber stopper. Why is it important to touch theobject to the metal rod and not to the rubber stopper?

Figure 10 Lightning strikes the lightning rod ratherthan the building because the lightning rod is thetallest point on the building.

REVIEW

Sprites and elves aren’t just creaturesin fairy tales! Read about how theyare related to lightning on page 451.


NSTA

TOPIC: Static ElectricityGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP405

Figure 11 This cell has a zinc electrode and acopper electrode dipped in a liquid electrolyte.

Chapter 17430

Electrical EnergyImagine living without electrical energy. You could not watchtelevision or listen to a portable radio, and you could not eventurn on a light bulb to help you see in the dark! Electricalenergy—the energy of electric charges—provides people withmany comforts and conveniences. A flow of charges is calledan electric current. Electric currents can be produced in manyways. One common way to produce electric current is throughchemical reactions in a battery.

Batteries Are IncludedIn science, energy is defined as the ability to do work. Energycannot be created or destroyed; it can only be converted intoother types of energy. A cell is a device that produces an elec-tric current by converting chemical energy into electricalenergy. A battery also converts chemical energy into electricalenergy and is made of several cells.

Parts of a Cell Every cell contains a mixture of chemicals thatconducts a current; the mixture is called an electrolyte(ee LEK troh LIET). Chemical reactions in the electrolyte con-vert chemical energy into electrical energy. Every cell also con-tains a pair of electrodes made from two different conductingmaterials that are in contact with the electrolyte. An electrode(ee LEK TROHD) is the part of a cell through which charges enteror exit. Figure 11 shows how a cell produces an electric current.

a

b

c

Flow

A chemical reaction leavesextra electrons on the zincelectrode. Therefore, the zincelectrode has a negativecharge.

A different chemical reactioncauses electrons to be pulledoff the copper electrode, mak-ing the copper electrode posi-tively charged.

If the electrodes areconnected by a wire,charges will flow fromthe negative zinc elec-trode through the wireto the positive copperelectrode, producing anelectric current.

Section

2

cell photocellbattery thermocouplepotential difference

Explain how a cell produces anelectric current.

Describe how the potentialdifference is related to electriccurrent.

Describe how photocells andthermocouples produce electricalenergy.


Types of Cells Cells are divided into two groups—wet cellsand dry cells. Wet cells, such as the cell shown in Figure 11,contain liquid electrolytes. A car battery is made of several wetcells that use sulfuric acid as the electrolyte.

Dry cells work in a similar way, but dry cells contain elec-trolytes that are solid or pastelike. The cells used in portableradios and flashlights are examples of dry cells.

You can make your owncell by inserting strips of zincand copper into a lemon.The electric current pro-duced when the metal stripsare connected is strongenough to power a smallclock, as shown in Figure 12.

Bring On the PotentialSo far you have learned that cells and batteries canproduce electric currents. But why does the elec-tric current exist between the two electrodes? Theelectric current exists because a chemical reactioncauses a difference in charge between the two elec-trodes. The difference in charge means that an elec-tric current—a flow of electric charges—can beproduced by the cell to provide energy. The energyper unit charge is called the potential difference andis expressed in volts (V).

As long as there is a potential differencebetween the electrodes of a cell and there is awire connecting them, charges will flow throughthe cell and the wire, creating an electric current. The current depends on the potential difference.The greater the potential difference is, the greaterthe current. Figure 13 shows batteries and cellswith different potential differences.

Figure 12 This cell uses thejuice of a lemon as an elec-trolyte and uses strips of zincand copper as electrodes.

431

Figure 13 Batteries are made withdifferent potential differences. Thepotential difference of a batterydepends on the number of cells itcontains.

Introduction to Electricity

Potatoes aren’t just for eatinganymore! Learn how to use a potato to produce an electric current on page 695 of the LabBook.

12 V battery

6 V battery

1.5 V cells9 V battery


Other Ways of Producing Electrical EnergyThe conversion of chemical energy to electrical energy in bat-teries is not the only way electrical energy can be generated.Several technological devices have been developed to convertdifferent types of energy into electrical energy for use everyday. For example, generators convert kinetic energy into elec-trical energy. Two other devices that produce electrical energyare photocells and thermocouples.

Photocells Have you ever wondered how a solar-powered cal-culator works? If you look above the display of the calculator,you will see a dark strip called a solar panel. This panel ismade of several photocells. A photocell is the part of a solarpanel that converts light into electrical energy.

Photocells contain silicon atoms.When light strikes the photocell,electrons are ejected from the siliconatoms. If light continues to shine onthe photocell, electrons will besteadily emitted. The ejected elec-trons are gathered into a wire to create an electric current.

Thermocouples Thermal energy canbe converted to electrical energy by athermocouple. A simple thermocoupleis made by joining wires made of twodifferent metals into a loop, as shownin Figure 14. The temperature differ-ence within the loop causes charges toflow through the loop. Thermocouplesare used to monitor the temperatureof car engines, furnaces, and ovens.

Chapter 17432

1. Name the parts of a cell, and explain how they worktogether to produce an electric current.

2. How do the currents produced by a 1.5 V flashlight celland a 12 V car battery compare?

3. Inferring Conclusions Why do you think some solarcalculators contain batteries?

Figure 14 A Simple Thermocouple

REVIEW

Copper wire

Burner Iron wire

Ice water

Meter

The greater the temperature differ-ence is, the greater the current.

Solar panel

One section of the loop is heated.

One section of theloop is cooled.

NSTA

TOPIC: Electrical EnergyGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP410


Figure 15 Electrons moving in awire make up current, a continu-ous flow of charge.


Electric CurrentSo far you have read how electrical energy can be generatedby a variety of methods. A battery produces electrical energyvery effectively, but electric power plants provide most of theelectrical energy used every day. In this section, you will learnmore about electric current and about the electrical energy youuse at home.

Current RevisitedIn the previous section, you learned that electric current is acontinuous flow of charge. Current is more precisely definedas the rate at which charge passes a given point. The higherthe current is, the more charge passes the point each second.The unit for current is the ampere (A), which is sometimescalled amp for short. In equations, the symbol for current isthe letter I.

Charge Ahead! When you flip a light switch, the light comeson instantly. Many people think that happens because elec-trons travel through the wire at the speed of light. In fact, it’sbecause an electric field is created at close to the speed of light.

Flipping the light switch sets up an electric field in the wirethat connects to the light bulb. The electric field causes the freeelectrons in the wire to move, as illustrated in Figure 15. Becausethe electric field is created so quickly, the electrons start mov-ing through the wire at practically the same instant. You canthink of the electric field as a kind of command to the electronsto “Charge ahead!” The light comes on instantly because theelectrons simultaneously obey this command. So the currentthat causes the bulb to light up is established very quickly, eventhough individual electrons move quite slowly. In fact, it maytake a single electron over an hour to travel 1 m through a wire.

Section

3

current resistancevoltage electric power

Describe electric current. Identify the four factors that

determine the resistance of anobject.

Explain how current, voltage,and resistance are related byOhm’s law.

Describe how electric power isrelated to electrical energy.


Let’s See, AC/DC . . . There are two different types of elec-tric current—direct current (DC) and alternating current (AC).In direct current the charges always flow in the same direction.In alternating current the charges continually switch from flowing in one direction to flowing in the reverse direction.Figure 16 illustrates the difference between DC and AC.

The electric current produced by batteries and cells is DC,but the electric current from outlets in your home is AC. Bothtypes of electric current can be used to provide electrical energy.For example, if you connect a flashlight bulb to a battery, thelight bulb will light. You can light a household light bulb byattaching it to a lamp and turning the lamp switch on.

Alternating current is used in homes because it is morepractical for transferring electrical energy. In the United States,the alternating current provided to households changes direc-tions 120 times each second.

VoltageThe current in a wire is determined by voltage. Voltage is thedifference in energy per unit charge as a charge moves betweentwo points in the path of a current. Voltage is another wordfor potential difference. Because voltage is the same as poten-tial difference, voltage is expressed in volts. The symbol forvoltage is the letter V. You can think of voltage as the amountof energy released as a charge moves between two points inthe path of a current. The higher the voltage is, the moreenergy is released per charge. The current depends on thevoltage. The greater the voltage is, the greater the current.

Figure 16 Unlike DC, chargescontinually change direction in AC.

Chapter 17434

Direct current has one direction.

Alternating currentcontinually changes

direction.


Voltage May Vary In the United States, electrical outletsusually supply a voltage of 120 V. Therefore, most electri-cal devices, such as televisions, toasters, lamps, and alarmclocks, are designed to run on 120 V. Devices that run onbatteries or cells usually need a lower voltage. For example,a portable radio needs only 3 V. Compare this with the volt-age created by the eel in Figure 17.

ResistanceIn addition to voltage, resistance also determines the currentin a wire. Resistance is the opposition to the flow of electriccharge. Resistance is expressed in ohms (Ω, the Greek letteromega). In equations, the symbol for resistance is the letter R.

You can think of resistance as “electrical friction.” Thehigher the resistance of a material is, the lower the currentis in it. Therefore, as resistance increases, current decreasesif the voltage is kept the same. An object’s resistance variesdepending on the object’s material, thickness, length, andtemperature.

Material Good conductors, such as copper, have low resis-tance. Poorer conductors, such as iron, have higher resistance.The resistance of insulators is so high that electric charges can-not flow in them.

Materials with low resistance are used to make wires andother objects that are used to transfer electrical energy fromplace to place. For example, most of the electrical cords inyour house contain copper wires. However, it is sometimeshelpful to use a material with high resistance, as shown inFigure 18.


Figure 17 An electric eel cancreate a voltage of more than600 V!

Figure 18 Tungsten light bulbfilaments have a high resistance.This property causes electricalenergy to be converted to lightand thermal energy.


Pacemaker cells in the heart producelow electric currents at regular inter-vals to make the heart beat. Duringa heart attack, pacemaker cells donot work together and the heartbeats irregularly. To correct this,doctors sometimes “jump start” the heart by creating a high voltageacross a person’s chest, which forcesthe pacemaker cells to act together,restoring a regular heartbeat.


Thickness and Length To understand how the thickness andlength of a wire affect the wire’s resistance, consider the modelin Figure 19. The pipe filled with gravel represents a wire, andthe water flowing through the pipe represents electric charges.This analogy illustrates that thick wires have less resistancethan thin wires and that long wires have more resistance thanshort wires.

Temperature Resistance also depends somewhat on tempera-ture. In general, the resistance of metals increases as tempera-ture increases. This happens because atoms move faster at highertemperatures and get in the way of the flowing electric charges.

If you cool certain materials to an extremely low tempera-ture, resistance will drop to nearly 0 Ω. Materials in this stateare called superconductors. A small superconductor is shown inFigure 20. Superconductors can be useful because very little

energy is wasted when electric charges travelin them. However, so much energy is neces-sary to cool them that superconductors arenot practical for everyday use.

Chapter 17436

Figure 20 One interesting property of super-conductors is that they repel magnets. Thesuperconductor in this photo is repelling themagnet so strongly that the magnet is floating.

A thick pipe has less resistance thana thin pipe because there are morespaces between pieces of gravel in athick pipe for water to flow through.

A short pipe has less resistance thana long pipe because the water in ashort pipe does not have to work itsway around as many pieces of gravel.

Figure 19 Gravel in a pipe is like resistance in a wire. Just as gravelmakes it more difficult for water to flow through the pipe, resistancemakes it more difficult for electric charges to flow in a wire.


Ohm’s Law: Putting It All Together

So far, you have learned about current,voltage, and resistance. But how are theyrelated? A German school teacher namedGeorg Ohm asked this very question. He determined that the relationshipbetween current (I), voltage (V), andresistance (R) could be expressed withthe equation shown at right. This equa-tion, which is known as Ohm’s law,shows that the units of current, voltage,and resistance are related in the follow-ing way:

amperes (A) ovhomlts

s((VΩ))

You can use Ohm’s law to find the cur-rent in a wire if you know the voltageapplied and the resistance of the wire.For example, if a voltage of 30 V is appliedto a wire with a resistance of 60 Ω, the current is as follows:

I VR

30 V60 Ω 0.5 A

Electric PowerYou probably hear the word power used in different ways. Powercan be used to mean force, strength, or energy. In science,power is the rate at which work is done. Electric power is therate at which electrical energy is used to do work. The unit forpower is the watt (W), and the symbol for power is the letterP. Electric power is calculated with the following equation:

power voltage current, or P V I

For the units:

watts (W) volts (V) amperes (A)


Using Ohm’s LawYou can use Ohm’s law tofind voltage or resistance:

V I R R VI

If a 2 A current flows througha resistance of 12 Ω, the volt-age is calculated as follows.

V I RV 2 A 12 ΩV 24 V

Now It’s Your Turn1. Find the resistance of an

object if a voltage of 10 Vproduces a current of 0.5 A.

2. Find the current producedif a voltage of 36 V isapplied to a resistance of 4 Ω.

MATH BREAK

I = RV


Watt Is a Power Rating?! If you have ever changed a lightbulb, you are probably familiar with watts. Light bulbs havelabels such as “60 W,” “75 W,” or “120 W.” As electrical energy

is supplied to a light bulb, the light bulb glows. As powerincreases, the bulb burns brighter because more

electrical energy is converted to light energy. Thatis why a 120 W bulb burns brighter than a

60 W bulb.Another common unit of power is the

kilowatt (kW). One kilowatt is equal to 1,000 W. Kilowatts are used to expresshigh values of power, such as the powerneeded to heat a house. The table showsthe power ratings of some appliances youuse every day.

Measuring Electrical EnergyElectric power companies sell electrical energy to homes andbusinesses. Such companies determine how much a householdor business has to pay based on power and time. For example,the amount of electrical energy used by a household dependson the power of the electrical devices in the house and howlong those devices are on. The equation for electrical energy isas follows:

electrical energy power time, or E P t

Power Ratings of Household Appliances

Chapter 17438

Self-CheckHow much electricalenergy is used by acolor television thatstays on for 2 hours?(See page 724 to checkyour answer.)

Appliance Power (W)

Clothes dryer 4,000

Toaster 1,100

Hair dryer 1,000

Refrigerator/freezer 600

Color television 200

Radio 100

Clock 3


How to Save Energy

The amount of electrical energy used by an appliance dependson the power rating of the appliance and how long it is on. Forexample, a clock has a power rating of 3 W, and it is on 24hours a day. Therefore, the clock uses 72 Wh (3 W 24 hours),or 0.072 kWh, of energy a day. Using the information in thetable on the previous page and an estimate of how long eachappliance is on during a day, determine which appliancesuse the most energy and which use the least. Based on yourfindings, describe what you can do to use less energy.

Measuring Household Energy Use Households use vary-ing amounts of electrical energy during a day. Electriccompanies usually calculate electric energy by multi-plying the power in kilowatts by the time in hours.The unit of electrical energy is usually kilowatt-hours(kWh). If a household used 2,000 W (2 kW) of powerfor 3 hours, it used 6 kWh of energy.

Electric power companies use electric meters suchas the one shown at right to determine the number ofkilowatt-hours of energy used by a household. Metersare often located outside houses and apartment buildingsso someone from the power company can read them.


1. What is electric current?

2. How does increasing the voltage affect the current?

3. How does an electric power company calculate electricalenergy from electric power?

4. Making Predictions Which wire would have the lowestresistance: a long, thin iron wire at a high temperatureor a short, thick copper wire at a low temperature?

5. Doing Calculations Use Ohm’s law to find the voltageneeded to produce a current of 3 A in a device with aresistance of 9 .

REVIEW

New England Electric1–888–555–5555

IN 33 DAYS YOU USEDREAD DATE01/21/0012/19/99DIFFERENCE

471 KWHMETER # 007905106059160120471

RATE CALCULATION:RESIDENTIAL SERVICE RATE, MULTI-FUEL

CUSTOMER CHARGE:ENERGY:FUEL:

SUBTOTAL ELECTRIC CHARGES

SALES TAXTOTAL COST FOR ELECTRIC SERVICE

FOR THIS 33 DAY PERIOD, YOUR

AVERAGE DAILY COST FOR ELECTRIC

SERVICE WAS $.91

$ 6.00

16.72

6.91$ 29.63

.30$ 29.93

471 KWH AT $.03550/KWH

471 KWH AT $.01467/KWH

DETACHHERE

DETACHHERE

PLEASE NOTIFY US 10 DAYS BEFORE MOVING

NSTA

TOPIC: Electric CurrentGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP415


Figure 21 Parts of a Circuit

Chapter 17440

Electric CircuitsImagine that you are lost in a forest. You need to find yourway back to camp, where your friends are waiting for you.Unfortunately, there are no trails to follow, so you don’t knowwhich way to go. Just as you need a trail to follow in orderto return to camp, electric charges need a path to follow inorder to travel from an outlet or a battery to the device it pro-vides energy to. A path that charges follow is called a circuit.

A circuit, however, is not exactly the same as a trail in aforest. A trail may begin in one place and end in another. Buta circuit always begins and ends in the same place, forming aloop. Because a circuit forms a loop, it is said to be a closedpath. So an electric circuit is a complete, closed path throughwhich electric charges flow.

Parts of a CircuitAll circuits consist of an energy source, a load, and wires toconnect the other parts together. A load is a device that useselectrical energy to do work. All loads offer some resistanceto electric currents and cause the electrical energy to changeinto other forms of energy such as light energy or kineticenergy. Figure 21 shows some examples of the different partsof a circuit.

Wires connect the otherparts of a circuit together.Wires are usually made ofconducting materials withlow resistance, such ascopper.

The energy source can be a battery, a photocell, athermocouple, or an electricgenerator at a power plant.

a

b

Examples of loads arelight bulbs, appliances,televisions, and motors.

c

Section

4

circuit series circuitload parallel circuit

Name the three essential partsof a circuit.

Compare series circuits withparallel circuits.

Explain how fuses and circuitbreakers protect your homeagainst short circuits and circuitoverloads.


Opening and Closing a Circuit Sometimes a circuit alsocontains a switch. A switch is used to open and close a cir-cuit. Usually a switch is made of two pieces of conductingmaterial, one of which can be moved, as shown in Figure 22.For charges to flow through a circuit, the switch must beclosed, or “turned on.” If a switch is open, or “off,” the loopof the circuit is broken and no charges can flow through thecircuit. Light switches, power buttons on radios, and even thekeys on calculators and computers work this way.

Types of CircuitsLook around the room for a moment, and count the numberof objects that use electrical energy. You probably found sev-eral objects, such as lights, a clock, and maybe a computer.All of the objects you counted are loads in a large circuit thatmay include several rooms in the building. In fact, most cir-cuits contain more than one load. The loads in a circuit canbe connected in two different ways—in series or in parallel.

Figure 22 You can turn a light bulb on and off by using a switch to close and open a circuit.


Self-CheckIs a microwave oven an example of a load? Why orwhy not? (See page 724 to check your answer.)

When the switch is closed, the twopieces of conducting materialtouch, allowing the electric chargesto flow through the circuit.

When the switch is open, the gapbetween the two pieces of conductingmaterial prevents the electric chargesfrom traveling through the circuit.


Believe it or not, your body is con-trolled by a large electric circuit.Electrical impulses from your braincontrol all the muscles and organs inyour body. The food you eat is theenergy source for your body’s circuit,your nerves are the wires, and yourmuscles and organs are the loads.


Series Circuits A series circuit is a circuit in which all partsare connected in a single loop. The charges traveling througha series circuit must flow through each part and can only fol-low one path. Figure 23 shows an example of a series circuit.

All the loads in a series circuit share the same current.Because the current in all the light bulbs in Figure 23 is thesame, the light bulbs glow with the same brightness. However,if you add more light bulbs, the resistance of the entire cir-cuit would increase and the current would decrease. Therefore,all the bulbs would be dimmer.

Uses for Series Circuits Some series circuits use a load as aswitch. For example, the automatic door at the grocery storeis operated by a series circuit with a motor that opens the doorand a photoelectric device—an “electric eye”—that acts as anon-off switch. When no light hits the device, charges flow tothe motor and the door opens.

For charges to flow in a series circuit, all the loads must beturned on and working. Charges pass through one load afteranother, in order, around the circuit. If one load is broken ormissing, the other loads will not work. For example, if a tele-vision and a table lamp were connected in series and the lampbroke, your television would go off. This would be a problemat home, but it is useful in wiring bank alarms, some types ofstreet lights, and certain computer circuits.

Chapter 17442

Figure 23 The charges flow from the battery through each light bulb(load) and finally back to the battery.

A Series of Circuits

1. Connect a 6 Vbattery and two flashlight bulbsin a series circuit.Draw a picture of your circuit in your ScienceLog.

2. Add another flashlightbulb in series with theother two bulbs. How doesthe brightness of the lightbulbs change?

3. Replace one of the lightbulbs with a burned-outlight bulb. What happensto the other lights in thecircuit?


Parallel Circuits Think about what would happen if all thelights in your home were connected in series. If you needed alight on in your room, all the other lights in the house wouldhave to be turned on too! Luckily, circuits in buildings are wiredin parallel rather than in series. A parallel circuit is a circuit inwhich different loads are located on separate branches. Becausethere are separate branches, the charges travel through morethan one path. Figure 24 shows a parallel circuit.

Unlike a series circuit, the loads in a parallel circuit do nothave the same current in them. Instead, each load in a par-allel circuit uses the same voltage. For example, the full volt-age of the battery is applied to each bulb in Figure 24. As aresult, each light bulb glows at full brightness, no matter howmany bulbs are connected in parallel. You can connect loadsthat require different currents to the same parallel circuit. Forexample, you can connect a hair dryer, which requires a highcurrent to operate, to the same circuit as a lamp, which requiresless current.

Uses for Parallel Circuits In a parallel circuit, each branchof the circuit can function by itself. If one load is broken ormissing, charges will still run through the other branches, andthe loads on those branches will continue to work. In yourhome, each electrical outlet is usually on its own branch, withits own on-off switch. It would be inconvenient if each timea light bulb went out, your television or stereo stopped work-ing. With parallel circuits, you can use one light or applianceat a time, even if another branch fails.


Figure 24 The electric charges flow from the battery to each ofthe bulbs separately and then flow back to the battery.

A Parallel Lab

1. Connect a 6 V battery and twoflashlight bulbs in a parallel circuit.Draw a picture ofyour circuit in yourScienceLog.

2. Add another flashlightbulb in parallel with theother two bulbs. How doesthe brightness of the lightbulbs change?

3. Replace one of the lightbulbs with a burned-outlight bulb. What happens to the other lights in thecircuit?


Household CircuitsIn every home, several circuits connect lights, major appli-ances, and outlets throughout the building. Most householdcircuits are parallel circuits that can have several loads attachedto them. The circuits branch out from a breaker box or a fusebox that acts as the “electrical headquarters” for the building.Each branch receives a standard voltage, which is 120 V inthe United States.

Mayday! Circuit Failure! Broken wires or water can causeelectrical appliances to short-circuit. A short circuit occurs whencharges bypass the loads in the circuit. When the loads are

bypassed, the resistance of the circuit drops, and thecurrent in the circuit increases. If the current

increases too much, it can produce enoughthermal energy to start a fire. Figure 25

shows how a short circuit might occur.

Circuits also may fail if they are overloaded. A circuit isoverloaded when too many loads, or electrical devices, areattached to it. Each time you add a load to a parallel circuit,the entire circuit draws more current. If too many loads areattached to one circuit, the current increases to an unsafe levelthat can cause the temperature of the wires to increase andcause a fire. Figure 26 shows a situation that can cause a cir-cuit overload.

Figure 25 If the insulating plastic arounda cord is broken, the two wires inside cantouch. The charges can then bypass theload and travel from one wire to the other.

Chapter 17444

Figure 26 Plugging too manydevices into one outlet cancause a circuit to overload.


Figure 28 GFCIdevices are usually

found on outlets inbathrooms and kitchens

to protect you from electric shock.

Circuit Safety Because short circuits and circuit overloads can be so danger-ous, safety features are built into the circuits in your home.The two most commonly used safety devices are fuses and cir-cuit breakers, which are located in a fuse box or a breaker box.

Fuses A fuse contains a thin strip of metal through whichthe charges for a circuit flow. If the current in the circuit is toohigh, the metal in the fuse warms up and melts, as shown inFigure 27. A break or gap in the circuit is produced, and thecharges stop flowing. This is referred to as blowing a fuse. Aftera fuse is blown, you must replace it with a new fuse in orderfor the charges to flow through the circuit again.

Circuit Breakers A circuit breaker is a switch that automat-ically opens if the current in the circuit is too high. If thecurrent in a circuit is too high, a strip of metal in the cir-cuit breaker warms up and bends away from the wires inthe circuit. A break in the circuit results. Open circuitbreakers can be closed easily by flipping a switch insidethe breaker box once the problem has been corrected.

A device that acts like a miniature circuit breakeris a ground fault circuit interrupter (GFCI). A GFCI,like the one shown in Figure 28, provides pro-tection by comparing the current in one sideof an outlet with the current in the other side.If there is even a small difference, the GFCIopens the circuit. To close the circuit, youmust push the RESET button.


Figure 27 The blown fuse onthe left must be replaced witha new fuse, such as the oneon the right.

1. Name and describe the three essential parts of a circuit.

2. Why are switches useful in a circuit?

3. What is the difference between series and parallel circuits?

4. How do fuses and circuit breakers protect your homeagainst electrical fires?

5. Developing Hypotheses Whenever you turn on theportable heater in your room, the circuit breaker for thecircuit in your room opens and all the lights go out.Propose two possible reasons for why this occurs.

REVIEW

NSTA

TOPIC: Electric CircuitsGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP420


Chapter Highlights

Chapter 17446

SECTION 1 SECTION 2

Vocabularylaw of electric charges (p. 423)

electric force (p. 423)

conduction (p. 425)

induction (p. 425)

conductor (p. 427)

insulator (p. 427)

static electricity (p. 427)

electric discharge (p. 428)

Section Notes

• The law of electric chargesstates that like charges repeland opposite charges attract.

• The electric force variesdepending on the size of thecharges exerting the forceand the distance betweenthem.

• Objects become chargedwhen they gain or lose elec-trons. Objects may becomecharged by friction, conduc-tion, or induction.

• Charges are not created ordestroyed and are said to beconserved.

• An electroscope can be usedto detect charges.

• Charges move easily inconductors but do not moveeasily in insulators.

• Static electricity is thebuildup of electric charges onan object. Static electricity islost through electric dis-charge. Lightning is a formof electric discharge.

• Lightning rods work bydirecting the electric chargecarried by lightning safely tothe Earth.

LabsStop the Static Electricity! (p. 694)

Vocabularycell (p. 430)

battery (p. 430)

potential difference (p. 431)

photocell (p. 432)

thermocouple (p. 432)

Section Notes

• Batteries are made of cellsthat convert chemical energyto electrical energy.

• Electric currents can beproduced when there is apotential difference.

• Photocells and thermo-couples are devices used toproduce electrical energy.

LabsPotato Power (p. 695)

Skills CheckMath ConceptsOHM’S LAW Ohm’s law, shown on page 437,describes the relationship between current,voltage, and resistance. If you know two of thevalues, you can always calculate the third. Forexample, the current in a wire with a resistanceof 4 Ω produced by a voltage of 12 V is calcu-lated as follows:

I VR 12 V

4 Ω 3 A

Visual UnderstandingSERIES AND PARALLELCIRCUITS There are two types of circuits—series and parallel. Thecharges in a series cir-cuit follow only onepath, but the charges ina parallel circuit followmore than one path.Look at Figures 23 and24 on pages 442–443 toreview series and parallel circuits.


447Introduction to Electricity

SECTION 3

Vocabularycurrent (p. 433)

voltage (p. 434)

resistance (p. 435)

electric power (p. 437)

Section Notes

• Electric current is a continu-ous flow of charge caused bythe motion of electrons.

• Voltage is the same as poten-tial difference. As voltageincreases, current increases.

• An object’s resistance variesdepending on the object’smaterial, thickness, length,and temperature. As resis-tance increases, currentdecreases.

• Ohm’s law describes the rela-tionship between current,resistance, and voltage.

• Electric power is the rate atwhich electrical energy doeswork. It is expressed in wattsor kilowatts.

• Electrical energy is electricpower multiplied by time. It is usually expressed inkilowatt-hours.

Vocabularycircuit (p. 440)

load (p. 440)

series circuit (p. 442)

parallel circuit (p. 443)

Section Notes

• Circuits consist of an energysource, a load, wires, andsometimes a switch.

• All parts of a series circuit areconnected in a single loop.

• The loads in a parallel circuitare on separate branches.

• Circuits can fail because of ashort circuit or circuitoverload.

• Fuses or circuit breakers pro-tect your home against cir-cuit failure.

LabsCircuitry 101 (p. 696)

SECTION 4


TOPIC: Static Electricity sciLINKS NUMBER: HSTP405

TOPIC: Electrical Energy sciLINKS NUMBER: HSTP410

TOPIC: Electric Current sciLINKS NUMBER: HSTP415

TOPIC: Electric Circuits sciLINKS NUMBER: HSTP420



KEYWORD: HSTELE




1. A ? converts chemical energy intoelectrical energy. (battery or photocell)

2. Charges flow easily in a(n) ? . (insulator or conductor)

3. ? is the opposition to the flow of elec-tric charge. (Resistance or Electric power)

4. A ? is a complete, closed path throughwhich charges flow. (load or circuit)

5. Lightning is a form of ? . (static electricity or electric discharge)


Multiple Choice

6. If two charges repel each other, the twocharges must bea. positive and positive.b. positive and negative.c. negative and negative.d.Either (a) or (c)

7. A device that can convert chemical energyto electrical energy is aa. lightning rod.b. cell.c. light bulb.d.All of the above

Chapter 17448

8. Which of the following wires has the lowest resistance?a. a short, thick copper

wire at 25°Cb. a long, thick copper wire at 35°Cc. a long, thin copper wire at 35°Cd.a short, thick iron wire at 25°C

9. An object becomes charged when theatoms in the object gain or losea. protons. c. electrons.b. neutrons. d. All of the above

10. A device used to protect buildings fromelectrical fires is a(n)a. electric meter. c. fuse.b. circuit breaker. d. Both (b) and (c)

11. In order to produce a current from a cell,the electrodes of the cell musta. have a potential difference.b. be in a liquid.c. be exposed to light.d.be at two different temperatures.

12. What type of current comes from the out-lets in your home? a. direct current c. electric dischargeb. alternating current d. static electricity

Short Answer

13. List and describe the three essential partsof a circuit.

14. Name the two factors that affect thestrength of electric force, and explain howthey affect electric force.

15. Describe how direct current differs fromalternating current.


Concept Mapping

16. Use the followingterms to create a con-cept map: electriccurrent, battery,charges, photocell,thermocouple, circuit, parallel circuit, series circuit.


17. Your science classroom was rewired overthe weekend. On Monday, you notice thatthe electrician may have made a mistake.In order for the fish-tank bubbler to work,the lights in the room must be on. And ifyou want to use the computer, you mustturn on the overhead projector. Describewhat mistake the electrician made withthe circuits in your classroom.

18. You can make a cell using an apple, astrip of copper, and a strip of silver.Explain how you would construct the cell, and identify the parts of the cell.What type of cell is formed? Explain your answer.

19. Your friend shows you a magic trick. Sherubs a plastic comb with a piece of silkand holds the comb close to a stream ofwater. When the comb is close to thewater, the water bends toward the comb.Explain how this trick works. (Hint: Thinkabout how objects become charged.)

MATH IN SCIENCE

Use Ohm’s law to solve the followingproblems:

20. What voltage is needed to produce a 6 Acurrent through a resistance of 3 Ω?

21. Find the current produced when a voltageof 60 V is applied to a resistance of 15 Ω.

22. What is the resistance of an object if avoltage of 40 V produces a current of 5 A?


23. Classify the objects in the photographbelow as conductors or insulators.




ReadingCheck-up


450

Riding the Electric Rails

For more than 100 years, the trolley, orstreetcar, was a popular way to travelaround a city. Then, beginning in the

1950s, most cities ripped up their trolley tracks tomake way for automobiles. Today, trolleys aremaking a comeback around the world.

From Horse Power to Electric PowerIn 1832, the first trolleys, called horsecars, werepulled by horses through the streets of New York.Soon horsecars were used in most large cities inthe United States. However, using horses forpower presented several problems. Among otherthings, the horses were slow and required specialattention and constant care. So inventors beganlooking for other sources of power.

In 1888, Frank J. Sprague developed a way tooperate trolleys with electrical energy. These elec-tric trolleys ran on a metal track and were con-nected by a pole to an overhead power line.Electric charges flowed down the pole to motorsin the trolley. A wheel at the top of the pole,called a shoe, rolled along the power line, allow-ing the trolley to move along its track withoutlosing contact with its power source. The chargespassed through the motor and then returned toa power generator by way of the metal track.

Taking It to the StreetsBy World War I, more than 40,000 km ofelectric-trolley tracks were in use in the UnitedStates. The trolley’s popularity helped shapeAmerican cities because businesses were builtalong the trolley lines. But competition fromcars and buses grew over the next decade,and many trolley lines were abandoned.

By the 1980s, nearly all of the trolley lineshad been shut down. But by then, people werelooking for new ways to cut down on the pollu-tion, noise, and traffic problems caused by auto-

mobiles and buses. Trolleys provided one pos-sible solution. Because they run on electricalenergy, they create little pollution, and becausemany people can ride on a single trolley, they cut down on traffic.

Today, a new form of trolley is being used ina number of major cities. These light-rail transitvehicles are quieter, faster, and more economicalthan the older trolleys. They usually run on railsalongside the road and contain new systems,such as automated brakes and speed controls.

Think About It! Because trolleys operate on electrical energy,does this mean that they don’t create any pollu-tion? Explain your answer.

Many cities across the country now uselight-rail systems for public transportation.

The horsecar was a popular mode of travelin many cities during the early 1900s.


451


Sprites and ElvesImagine you are a pilot flying a plane on amoonless night. About 80 km away, younotice a powerful thunderstorm and see thelightning move between the clouds and theEarth. This makes sense because you knowthat all weather activity takes place in the low-est layer of Earth’s atmosphere, which is calledthe troposphere. But all of a sudden, a ghostlyred glow stretches many kilometers above thestorm clouds and into the stratosphere!

Capturing SpritesIn 1989, scientists at the University of Minnesotafollowed the trail of many such reports. Theycaptured the first image of this strange, red-glowing lightning using a video camera. Sincethen, photographs from space shuttles, airplanes,telescopes, and observers on the ground haveidentified several types of wispy electrical glows.Two of these types were named sprites and elvesbecause, like the mythical creatures, they lastonly a few thousandths of a second and disap-pear just as the eye begins to see them.

Photographs show that sprites and elvesoccur only when ordinary lightning is dischargedfrom a cloud. Sprites are very large, extendingfrom the cloud tops at an altitude of about 15 kmto as high as 95 km. They are up to 50 km wide.Elves are expanding disks of red light, probablycaused by an electromagnetic pulse from light-ning or sprites. Elves can be 200 km across, andthey appear at altitudes above 90 km.

What Took So Long?It is likely that sprites and elves have been occur-ring for thousands of years but went unrecorded.This is because they are produced with onlyabout 1 percent of lightning flashes. They alsolast for a short period of time and are very faint.Since they occur above thunderclouds, wherefew people can see, observers are more oftendistracted by the brighter lightning below.

Still, scientists are not surprised to learn thatelectric discharges extend up from clouds.There is a large potential difference betweenthunderclouds and the ionosphere, an atmos-pheric level above the clouds. The ionosphere iselectrically conductive and provides a path forthese electric discharges.

Search and Find Would you like to find sprites on yourown? (Elves disappear too quickly.) Go withan adult, avoid being out in a thunderstorm,and remember: It must be completely dark, and your eyes

must adjust to the total darkness. Viewing is best when a large thunderstorm

is 48 to 97 km away, with no clouds inbetween.

Block out the lightning below the cloudswith dark paper so that you can still seeabove the clouds.

Be patient.Report sightings to a university geophysical

department. Scientists need more informationto fully understand how these discharges affectthe chemical and electrical workings of ouratmosphere.

Sprites (left) and elves (right) are strangeelectric discharges in the atmosphere.


452 Chapter 18

Magnets andMagnetism . . . . . . . . . 454

QuickLab . . . . . . . . . . 459Biology Connection . . 460Internet Connect . . . . 461

Magnetism from Electricity . . . . . . . . . . 462

Apply . . . . . . . . . . . . . 463QuickLab . . . . . . . . . . 464Internet Connect . . . . 467

Electricity from Magnetism . . . . . . . . . 468


Chapter Review . . . . . . . . . . 476


LabBook . . . . . . . . . . . 698–701

ElectromagnetismElectromagnetism


1. What are the propertiesof magnets?

2. How does electricity produce magnetism?

3. How does magnetism produce electricity?


453

MAGNETIC ATTRACTIONIn this activity, you will investigateways you can use a magnet to lift steel.

Procedure

1. Place 5 steel paper clips on yourdesk. Touch the clips with anunmagnetized iron nail. Lift thenail and record the number ofclips that stick to the nail.

2. Touch the clips with the end of astrong bar magnet. Record thenumber of clips that stick to it.

3. While holding the magnet againstthe head of the nail, touch the tipof the nail to the paper clips.Count the number of paper clipsthat stick to the nail.

4. Remove the magnet from the endof the nail, and observe what hap-pens. Record the number of paperclips you counted in step 3 andyour observations from step 4.

5. Drag one end of the bar magnet50 times down the nail. Drag themagnet in only one direction.

6. Set the magnet aside. Touch thenail to the clips. Record the num-ber of clips that stick to it.

Analysis

7. What caused the differencebetween the number of paper clipsyou picked up in step 1 and step 3?

8. What effect did the magnet haveon the nail in step 5?

Electromagnetism

Electric High Speed trainsMeet the Eurostar, an electric passenger trainthat runs at speeds up to 298 kilometers perhour (186 mph). The Eurostar railway connectsFrance, England, and Belgium, traveling throughthe “Chunnel,” a 50-kilometer (30-mile)-longtunnel under the English Channel. The train getsits electrical power either through a third railbeneath the train or through overhead wires. Inthis chapter, you will learn how electricity andmagnetic force are related, how electric motorswork, and how electrical power is generated.


Section

1

magnetpolesmagnetic force

Describe the force between twomagnetic poles.

Explain why some materials aremagnetic and some are not.

Describe four different categories of magnets.

Give two examples of the effect of Earth’s magnetic field.

Figure 1 More paper clips stick tothe ends, or poles, of a magnetbecause that’s where the magneticeffects are strongest.

Chapter 18454

Magnets and MagnetismYou’ve probably seen magnets like the onesat right and below, stuck to a refrigeratordoor. These magnets might have been usedto hold up notes or pictures or might havebeen used just for decoration. If you haveever played with magnets, you know thatthey stick to each other and to sometypes of metals. You also know that mag-nets can stick to objects withoutdirectly touching them—like when oneis used to hold a piece of paper to arefrigerator door. How do magnetswork? Read on to find out.

Properties of MagnetsMore than 2,000 years ago, the Greeks discovered a mineralthat attracted objects containing iron. Because this mineralwas found in a part of Turkey called Magnesia, the Greekscalled it magnetite. Today any material that attracts iron ormaterials containing iron is called a magnet. All magnets havecertain properties. For example, all magnets have two poles,exert forces, and are surrounded by a magnetic field.

Magnetic Poles The magnetic effects of a magnet are notevenly distributed throughout the magnet. For example, if youdip a bar magnet into a box of paper clips, you will find thatmost of the paper clips stick to the ends of the bar, as shownin Figure 1. As you can see, the magnetic effects are strongestnear the ends of the bar magnet. The parts of a magnet wherethe magnetic effects are strongest are called poles.



North and South If you attacha magnet to a string so that themagnet is free to rotate, you willsee that one end of the magnetalways ends up pointing to thenorth, as shown in Figure 2. Thepole of a magnet that points to thenorth is called the magnet’s northpole. The opposite end of the mag-net points to the south and is there-fore called the magnet’s south pole.Magnetic poles always occur inpairs; you will never find a magnetwith only a north pole or only asouth pole.

Magnetic Forces When you bring two magnets close together,the magnets each exert a force that can either push the mag-nets apart or pull them together. The force of repulsion or attrac-tion between the poles of magnets is called the magnetic force.The magnetic force between a pair of magnets depends on howthe poles of the magnets line up, as shown in Figure 3. As youcan see, magnetic poles are similar to electric charges in thatlike poles repel and opposite poles attract.

Figure 3 Magnetic Force Between Magnets

Electromagnetism 455

If you hold the north poles of two magnets closetogether, the magnetic force will push the magnetsapart. The same is true if you hold the south polesclose together.

If you hold the north pole of onemagnet close to the south pole ofanother magnet, the magnetic forcewill pull the magnets together.

Figure 2 The needle in a compassis a magnet that is free to rotate.

S N SN SS N S NSNN


Magnetic Fields A magnetic fieldexists in the region around a mag-net in which magnetic forces canact. The shape of a magnetic fieldcan be shown with lines drawnfrom the north pole of a magnetto the south pole, as shown inFigure 4. These lines map thestrength of magnetic force and arecalled magnetic field lines. Thecloser together the field lines are,the stronger the magnetic field is.Magnetic field lines around a mag-net are closest together at the poles,showing that the magnetic force isstrongest at these two places.

What Makes Materials Magnetic?Some materials are magnetic, and some are not. For example,a magnet can pick up objects such as paper clips and ironnails, but it cannot pick up paper, plastic, pennies, or alu-minum foil. What causes the difference? Whether a materialis magnetic depends on the atoms in the material.

Atoms and Domains All matter is composed of atoms. Inthe atoms, electrons are the negatively charged particles thatmove around the nucleus. Moving electrons produce magneticfields that can give an atom a north and a south pole. In mostmaterials, such as copper and aluminum, the magnetic fieldsof the individual atoms cancel each other out, so the materi-als aren’t magnetic. However, in materials like iron, nickel, andcobalt, the atoms group together in tiny regions called domains.The atoms in a domain are arranged so that the north andsouth poles of all the atoms line up and create a strong mag-netic field. Domains are like tiny magnets of different sizeswithin an object. Figure 5, on the next page, shows howdomains affect the magnetic properties of an object.

Chapter 18456

Figure 4 Magnetic field lines show theshape of a magnetic field around a mag-net. You can model magnetic field lines bysprinkling iron filings around a magnet.

Grazing cows sometimes eatpieces of metal that havefallen on the ground. To pro-tect their cows, ranchershave them swallow specialcow magnets. These mag-nets stay in one of the cow’sstomachs and attract anymetal objects containingiron that the cow eats. Thiskeeps the metal from travel-ing through the rest of thecow’s digestive system.


Losing Alignment The domains of a magnet may not alwaysstay aligned. Dropping a magnet or striking it too hard canjostle the domains out of alignment, causing the magnet tolose its magnetic properties. Increasing the temperature of amagnet can also demagnetize it. At higher temperatures, atomsin the magnet vibrate faster and lose their alignment withinthe domains.

Making Magnets A magnet can be made from an unmag-netized object made of iron, cobalt, or nickel by aligning thedomains in the object. For example, you can magnetize aniron nail if you rub it in one direction with one pole of a mag-net. The magnetic field of the magnet will cause the domainsin the nail to rotate and align with the domains in the mag-net. As more domains become aligned, the overall magneticfield of the nail will strengthen, and the nail will becomea magnet, as shown in Figure 6.

The process of making a magnet also explains how amagnet can pick up an unmagnetized object, such as apaper clip. When you hold a magnet close to a paper clip,the magnetic field of the magnet causes the domains inthe paper clip to align slightly, creating a temporarymagnet. The domains align such that the north pole ofthe paper clip points toward the south pole of the mag-net. The paper clip is therefore attracted to the magnet.The domains of the paper clip return to a randomarrangement after the magnet is removed.


Figure 5 The arrangement of domains in anobject determines whether the object is magnetic.

If the domains in an object are randomlyarranged, the magnetic fields of the individualdomains cancel each other out, and the objectoverall has no magnetic properties.

If most of the domains in an object arealigned, the magnetic fields of the individ-ual domains combine to make the wholeobject magnetic.

Figure 6 This nail wasmagnetized by rubbingit with a magnet.

Half a Magnet? What do you think would happen if youcut a magnet in half? You might predict that you would endup with one north-pole piece and one south-pole piece. Butthat’s not what happens. When you cut a magnet in half, youend up with two magnets, each with its own north pole andsouth pole, as shown in Figure 7. Each domain within a mag-net is like a tiny magnet with a north and south pole, so eventhe smallest pieces of a magnet have two poles.

Types of MagnetsThere are different ways to describe magnets. The magnets youmay be most familiar with are those made of iron, nickel,cobalt, or alloys of those metals. Magnets made with thesemetals have strong magnetic properties and are called ferro-magnets. The mineral magnetite, which you read about at thebeginning of this section and which is shown in Figure 8, isan example of a naturally occurring ferromagnet. Another typeof magnet is the electromagnet. An electromagnet is a magnet,usually with an iron core, produced by an electric current. Youwill learn more about electromagnets in the next section.

Figure 8 Magnetite attractsobjects containing iron and is a ferromagnet.


1. Name three properties of magnets.

2. Why are some iron objects magnetic and others notmagnetic?

3. Applying Concepts Suppose you have two bar magnets.One has its north and south poles marked, but the otherone does not. Describe how you could use the first mag-net to identify the poles of the second magnet.

REVIEW

Figure 7 If you cut a magnet intopieces, each piece will still be amagnet with two poles.


Temporary and Permanent Magnets Magnets can also bedescribed as temporary magnets or permanent magnets.Temporary magnets are made from materials that are easy to mag-netize but tend to lose their magnetization easily. Soft iron (ironthat is not mixed with any other materials) can be made intotemporary magnets. Permanent magnets, on the other hand, aredifficult to magnetize but tend to retain their magnetic prop-erties better. Strong permanent magnets are made with alnico(AL ni KOH)—an alloy of aluminum, nickel, and cobalt.

Earth as a MagnetRecall that one end of every magnet points to the north ifthe magnet is allowed to rotate freely. For more than 2,000years, travelers and explorers have relied on this to help themnavigate. In fact, you take advantage of this property anytime you use a compass, because a compass contains a freelyrotating magnet. But why do magnets point to the north?Read on to find out.

One Giant Magnet In 1600, an English physician namedWilliam Gilbert suggested that magnets point to the northbecause Earth itself is one giant magnet. In fact, Earth behavesas if it has a bar magnet running through its center. The polesof this imaginary magnet are located near Earth’s geographicpoles, as shown in Figure 9.

Figure 9 The magnetic poles of Earth are close to—but not thesame as—the geographic poles.

Geographic North Pole Magnetic pole

Magnetic pole Geographic South Pole


Earth’s geographicpoles are on the axison which Earth rotates.

The magnetic field linesaround Earth are similar tothe magnetic field linesaround a bar magnet.

Earth’s magnetic poles arethe points on Earth’s surfacewhere its magnetic forcesare the strongest.

Model of Earth’s Magnetic Field

1. On a sheet ofbutcher paper,draw a circle with adiameter larger than a barmagnet. This representsthe surface of the Earth.Label Earth’s North andSouth Poles.

2. Place a bar magnet underthe butcher paper and lineit up with the poles.

3. Sprinkle some iron filingslightly around the perim-eter of the circle. In yourScienceLog, describe andsketch the pattern you see.


North or South? Try this simple experiment. Place a com-pass on a bar magnet that has its north and south poles marked.Which pole of the magnet did the marked end of the needleof the compass point to? If your compass is working properly,the marked end should have pointed to the south pole of themagnet, as shown in Figure 10.Does that surprise you? Thinkabout what you have alreadylearned about magnets.

One property of magnets is that opposite poles attract eachother. That means that the north pole of one magnet is attractedto the south pole of another magnet. A compass needle is asmall magnet, and the tip that points to the north is the nee-dle’s north pole. Therefore, the point of a compass needle willbe attracted to the south pole of a bar magnet.

North Is South! So why does the needle of a compass pointnorth? The answer is that the magnetic pole of Earth that isclosest to the geographic North Pole is actually a magneticsouth pole! So a compass needle points to the north becauseits north pole is attracted to a very large magnetic south pole.

The Core of the Matter Although you can think of Earthas having a giant bar magnet in its center, as shown in

Figure 11, there isn’t really a magnet there. The tempera-ture of Earth’s core (or center) is so high that atomsin it move too violently to remain aligned in domains.

Scientists think that the Earth’s magnetic field isproduced by the movement of electric charges in theEarth’s core. The Earth’s core is made mostly of ironand nickel. The inner core is solid because it is undersuch great pressure. In the outer core, the pressure is

less and the metals are in a liquid state. As Earthrotates, the liquid in the core flows and causes electric

charges to move, creating a magnetic field.

460

Figure 10 The marked endof a compass needle alwayspoints to the south pole of a magnet.

Figure 11 The Earth actslike a giant magnet.

Chapter 18


Scientists think that birds may use theEarth’s magnetic field to help themnavigate. Tiny pieces of magnetite havebeen found in the brains of birds,which could help them sense whichdirection is north as they fly.

A Magnetic Light Show One of the most spectacular effectscaused by the Earth’s magnetic field is a curtain of light calledan aurora, like the one shown in Figure 12. An aurora isformed when charged particles from the sun interact withoxygen and nitrogen atoms in Earth’s atmosphere. Whencharged particles from the sun strike these atoms, the atomsemit light of different colors.

Earth’s magnetic field acts like a barrier to most chargedparticles from the sun, so the particles cannot strike the atmos-phere in most places. But because Earth’s magnetic field bendsinward at the magnetic poles, the charged particles can crashinto the atmosphere at and near the poles. Therefore, auro-ras are most often seen in areas near the north and southmagnetic poles. Auroras seen near the north magnetic poleare called aurora borealis (ah ROHR uh BOHR ee AL is), thenorthern lights, and auroras seen near the south magneticpole are called aurora australis (ah ROHR uh ah STRAY lis),the southern lights.

Figure 12 The photo at leftshows what an aurora looks likefrom the ground.

Electromagnetism 461Copyright © by Holt, Rinehart and Winston. All rights reserved.

1. Name the metals used to make ferromagnets.

2. How are temporary magnets different from permanentmagnets?

3. Applying Concepts Why are auroras more commonlyseen in places like Alaska and Australia than in placeslike Florida and Mexico?

REVIEW

Auroras are a result of geomagneticstorms. Read more about thesestorms on page 478.


NSTA

TOPIC: Magnetism, Types of MagnetsGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP430, HSTP435


Section

2

electromagnetismsolenoidelectromagnetelectric motor

Identify the relationship betweenan electric current and a mag-netic field.

Compare solenoids, electro-magnets, and magnets.

Describe how electromagnetismis involved in the operation ofdoorbells, electric motors, andgalvanometers.

Figure 13 Oersted’s experimentsshow that an electric current canmove a compass needle.

Chapter 18462

Magnetism from ElectricityMost of the trains you see roll on wheels on top of a track.But engineers have developed trains that have no wheels andactually float above the track. These trains are able to levi-tate because of magnetic forces between the track and thetrain cars. Such trains are called maglev trains. The namemaglev is short for magnetic levitation. To levitate, maglevtrains use a type of magnet called an electromagnet, whichcan produce a strong magnetic field. In this section you willlearn how electricity and magnetism are related and howelectromagnets are made.

The Discovery of ElectromagnetismDanish physicist Hans Christian Oersted discovered the rela-tionship between electricity and magnetism in 1820. Duringa lecture, he held a compass near a wire carrying an electriccurrent. Oersted noticed that when the compass was close tothe wire, the compass needle no longer pointed to the north.This result surprised Oersted because a compass needle is amagnet and only moves from its usual north-south orienta-tion when it is in a magnetic field different from Earth’s mag-netic field. Oersted tried a few experiments with the compassand the wire and found the results shown in Figure 13.

If no electric current exists inthe wire, the compass needlespoint in the same direction.

Electric current in one directionin the wire causes the com-pass needles to deflect in aclockwise direction.

Electric current in the oppositedirection makes the compassneedles deflect in a counter-clockwise direction.

a b c


More Research From his experi-ments, Oersted concluded that anelectric current produces a mag-netic field and that the directionof the magnetic field depends onthe direction of the current. TheFrench scientist André-MarieAmpère heard about Oersted’sfindings and did more researchwith electricity and magnetism.Together, their work was the firstresearch conducted on electro-magnetism. Electromagnetism isthe interaction between electric-ity and magnetism.

Using ElectromagnetismAlthough the magnetic field created by an electric current ina wire may deflect a compass needle, it is not strong enoughto be very useful. However, two devices, the solenoid and the electromagnet, strengthen the magnetic field created by acurrent-carrying wire. Both devices make electromagnetismmore useful for practical applications.

Solenoids The scientists mentioned at the beginning of thischapter used a solenoid to levitate a frog. A solenoid is a coil ofwire that produces a magnetic field when carrying an electriccurrent. A single loop of wire carrying a current does not havea very strong magnetic field. However, if many loops are usedto form a coil, the magnetic fields of the individual loops cancombine to produce a much stronger magnetic field. In fact, themagnetic field around a solenoid is very similar to themagnetic field of a bar magnet, as shown inFigure 14. The strength of the magnetic fieldproduced by a solenoid increases as moreloops are added and as the currentin the wire is increased.


Compasses Near Magnets

If you try to use a compass neardevices that have strong magnets,electromagnets, or electric motors,such as stereo speakers, radios, and televisions, you mightnotice that the needle of the compass does not alwayspoint to the north. Use the results from Oersted’s experi-ments to explain why this occurs. Why do you think it isimportant for a boater to keep the navigation compassaway from the boat’s radio?

Figure 14 The ends of the solenoidare like the poles of a magnet.


Electromagnets An electromagnet is a magnet that consistsof a solenoid wrapped around an iron core. The magnetic fieldproduced by the solenoid causes the domains inside the ironcore to become better aligned. The magnetic field for the entireelectromagnet is the field produced by the solenoid plus thefield produced by the magnetized iron core. As a result, themagnetic field produced by an electromagnet may be hun-dreds of times stronger than the magnetic field produced byjust a solenoid with the same number of loops.

The strength of an electromagnet can be made even strongerby increasing the number of loops in the solenoid, by increas-ing the size of the iron core, and by increasing the electriccurrent in the wire. Some electromagnets are strong enoughto lift a car or levitate a train!

Heavy Lifting Do you remember the maglev trains discussedat the beginning of this section? Those trains levitate becausethere are strong magnets on the cars that are repelled by pow-erful electromagnets in the rails. Electromagnets are particu-larly useful because they can be turned on and off as needed.Electromagnets attract objects containing iron only when acurrent exists in the wire. When there is no current in thewire, the electromagnet is turned off. Figure 15 shows an exam-ple of how this property can be useful.

Chapter 18464

Figure 15 The electromagnetsused in salvage yards can liftheavy scrap metal when turnedon. To put the metal back down,the electromagnet is turned off.

Self-CheckCan you make an elec-tromagnet by wrappinga coil of wire around awooden core? Explainyour answer.(See page 724 to checkyour answer.)

Electromagnets

1. Tightly wrap an insulated copperwire around a largeiron nail, leaving 10 cm ofwire loose at each end.

2. Remove the insulation fromthe ends of the wire, anduse electrical tape toattach the ends against thetop and bottom of a D-cell.

3. Hold the end of the nailnear some paper clips,and try to lift them up.

4. While holding the clips upwith your electromagnet,remove the wires from thecell.



Magnetic Force and Electric CurrentAt the beginning of this section you learned that an electriccurrent can cause a compass needle to move. The needle, asmall magnet, moves because the electric current in a wire cre-ates a magnetic field that exerts a force on the needle. If acurrent-carrying wire causes a magnet to move, can a magnetcause a current-carrying wire to move? Figure 16 shows thatthe answer is yes.

Applications of ElectromagnetismElectromagnetism is useful in your everyday life. You alreadyknow that electromagnets can be used to lift heavy objectscontaining iron. But did you know that you use a solenoidwhenever you ring a doorbell or that there are electromagnetsin motors? Keep reading to learn how electromagnetism makesthese devices work.

Doorbells Many doorbells containa solenoid with an iron rod insertedpart way in it. The electric current inthe solenoid is controlled by the door-bell button. When you press the but-ton, a switch in the solenoid circuitcloses, creating an electric current inthe solenoid. What happens next isshown in Figure 17.


Figure 16 A magnet exerts a force on a current-carrying wire.

When a current-carrying wire isplaced between two poles of amagnet, the wire will jump up.

If the direction of the electric currentin the wire is reversed, the wire ispushed down instead of up.

a b

Figure 17 An electric current in thesolenoid of a doorbell produces a

magnetic field. This field pullsthe iron rod through the

solenoid, and the rodstrikes the bell.


Electric Motors An electric motor is a device that changeselectrical energy into kinetic energy. All electric motors havean armature—a loop or coil of wire that can rotate. The arma-ture is mounted between the poles of a permanent magnet orelectromagnet.

In electric motors that use direct current, a device called acommutator is attached to the armature to reverse the direc-tion of the electric current in the wire. A commutator is a ringthat is split in half and connected to the ends of the arma-ture. Electric current enters the armature through brushes thattouch the commutator. Every time the armature and the com-mutator make a half-turn, the direction of the current isreversed. Figure 18 shows how a direct-current motor works.

Chapter 18466

Figure 18 A Direct-Current Electric Motor

Running the Motor As the arma-ture rotates, the commutator causesthe electric current in the coil tochange directions. When the electriccurrent is reversed, the side of thecoil that was pulled up is pulleddown, and the side that was pulleddown is pulled up. This keeps thearmature rotating.

Getting Started An electric current in thearmature causes the magnet to exert aforce on the armature. Because of thedirection of the current on either side ofthe armature, the magnet pulls up on oneside and down on the other. This makesthe armature rotate.

Permanentmagnet

Brushes

Commutator

Armature

Direction ofrotation

Source of electrical energy

N

S

N

S


30 302020 10 100

Galvanometers A galvanometer is a device used to measurecurrent through the interaction of an electromagnet and a per-manent magnet. Galvanometers are sometimes found in equip-ment used by electricians, such as ammeters and voltmeters.Galvanometers contain an electromagnet placed between thepoles of a permanent magnet. The electromagnet is free to rotateand is attached to a pointer. The pointer moves along a scalethat shows the size and direction of the current. When thereis a current in the coil of the electromagnet, the poles of theelectromagnet are repelled by the poles of the permanentmagnet. Figure 19 shows how the parts of a galvanometer work.


1. Describe what happens when you hold a compass closeto a wire carrying a current.

2. How is a solenoid like a bar magnet?

3. What makes the armature in an electric motor rotate?

4. Explain how a solenoid works to make a doorbell ring.

5. Applying Concepts What do Hans Christian Oersted’sexperiments have to do with a galvanometer? Explainyour answer.

REVIEW

Figure 19 The pointer will movefarther when there is a large cur-rent in the electromagnet thanwhen there is a small current.

Scale Pointer Electromagnet

Permanent magnet

NS

NSTA

TOPIC: ElectromagnetismGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP440


Section

3

electromagnetic inductiongeneratortransformer

Explain how a magnetic fieldcan produce an electric current.

Explain how electromagneticinduction is used in a generator.

Compare step-up and step-downtransformers.

Chapter 18468

Electricity from MagnetismWhen you use an electric appliance or turn on a light in yourhome, you probably don’t think about where the electricalenergy comes from. For most people, an electric power com-pany supplies their home with electrical energy. In this sec-tion, you’ll learn how a magnetic field can produce an electriccurrent and how power companies use this process to supplyelectrical energy.

Electric Current from a Magnetic FieldAfter Oersted discovered that an electric current could producea magnetic field, scientists began to wonder if a magnetic fieldcould produce an electric current. In 1831, two scientists—Michael Faraday, from Great Britain, and Joseph Henry, fromthe United States—independently solved this problem.Although Henry was the first to make the discovery, Faraday’sresults are better known because Faraday published his resultsfirst and reported them in greater detail.

Faraday’s Failure? In his experiments, Faraday used a setupsimilar to the one shown in Figure 20. Faraday hoped that themagnetic field created by the electromagnet would create—orinduce—an electric current in the second wire. But no matterhow strong the electromagnet was, no electric current couldbe produced in the second wire.

Figure 20 Faraday’s Setup

One wire was wound aroundone half of an iron ring.

A battery supplied an electric currentto the wire, making an electromagnet.

A galvanometer measured any current producedin the second wire by the magnetic field.

A second wire was wound aroundthe other half of the iron ring.

Success for an Instant As Faraday experimented with thiselectromagnetic ring, he noticed something interesting. At theinstant he connected the wires of the electromagnet to thebattery, the galvanometer pointer moved, indicating that anelectric current was present. The pointer moved again at theinstant he disconnected the electromagnet. But as long as theelectromagnet was fully connected to the battery, the gal-vanometer measured no electric current.

Faraday realized that electric current in the second wirewas produced only when the magnetic field was changing—in this case, when the magnetic field was turned on and offas the battery was connected and disconnected. The processby which an electric current is produced by a changing mag-netic field is called electromagnetic induction. Faraday did manymore experiments on electromagnetic induction. Some of hisresults are summarized in Figure 21.

A greater electric current is induced if youmove the magnet faster through the coilbecause the magnetic field is changing faster.

An electric current is induced when youmove a magnet through a coil of wire.

A greater electric current is induced if youadd more loops of wire. This magnet is mov-ing at the same speed as the magnet in (b).

The induced electric currentreverses direction if the magnet ispulled out rather than pushed in.

Electromagnetism 469Copyright © by Holt, Rinehart and Winston. All rights reserved.

Figure 21 The size and direction of the electric current inducedby a changing magnetic field depends on several factors.

a b

c d

You too can have instantsuccess with the activity onpage 699 of the LabBook.


Inducing Electric Current Faraday’s experimentsalso showed that the magnetic field around a wirecan be changed by moving either the magnet orthe wire. Therefore, an electric current could beinduced by moving a magnet in a coil of wire orby moving a wire between the poles of a magnet.

One way to remember when an electric cur-rent is produced by electromagnetic induction isto consider the magnetic field lines between thepoles of the magnet. An electric current is inducedonly when a wire cuts through, or crosses, themagnetic field lines, as shown in Figure 22. Thisis because the magnetic force causes electriccharges to move through the wire as the wiremoves through the magnetic field.

Applications of Electromagnetic InductionElectromagnetic induction is very important for the produc-tion of electrical energy at an electric power plant, and it isimportant for the transmission of energy from the plant toyour home. Generators and transformers work on the princi-ple of electromagnetic induction and are used by power plantsto provide the electrical energy that you need every day.

Generators A generator is a device that uses electromagneticinduction to convert kinetic energy into electrical energy.Figure 23 shows the parts of a simple generator, and Figure 24,on the next page, explains how the generator works.

Chapter 18470

Figure 23Parts of a Simple Generator

Generators contain a coil of wireattached to a rod that is free torotate. This generator has a crankthat is used to turn the coil.

The coil is placedbetween the poles of apermanent magnet orelectromagnet.

Slip rings are attached to theends of the wire in the coil.

Electric current leaves thegenerator when the slip rings touch a pair of brushes.

Figure 22 As the wire moves between the poles of the magnet, it cuts through magnetic field lines, and an electric current is induced.


Alternating Current The electric current produced by thegenerator shown in Figure 24 changes direction each time thecoil makes a half-turn. Because the electric current continu-ally changes direction, the electric current is an alternatingcurrent. Generators in power plants also produce alternatingcurrent. But generators in power plants are much larger andcontain many coils of wire instead of just one. In most largegenerators, the magnet is turned instead of the coils.

Generating Electrical Energy The energythat generators convert to electrical energycomes from different sources. In nuclearpower plants, thermal energy from anuclear reaction boils water to producesteam, which turns a turbine. The tur-bine turns the magnet of the genera-tor, inducing an electric current andgenerating electrical energy. Figure 25shows a similar process in a hydro-electric power plant.

As the coil continues to rotate,the magnetic field lines are cutfrom a different direction, andan electric current is induced inthe opposite direction.

Figure 25 As water flows down achute, it turns a turbine. The turbinespins the magnet of the generator,inducing an electric current.

When the coil is not cut-ting through the magneticfield lines, no electriccurrent is induced.

As the crank is turned, therotating coil cuts through themagnetic field lines of themagnet, and an electric cur-rent is induced in the wire.

Figure 24 How a Generator Works


1 2 3

Transformers Another device that relies on electromagneticinduction is a transformer. A transformer increases or decreasesthe voltage of an alternating current. A simple transformerconsists of two coils of wire wrapped around an iron ring.

Alternating current from an electrical energy source is sup-plied to one coil, called the primary coil. The electric currentmakes the ring an electromagnet. But the electric current inthe primary coil is alternating, so the magnetic field of theelectromagnet changes with every change in electric currentdirection. The changing magnetic field in the iron ring inducesan electric current in the other coil, called the secondary coil.

Step-Up, Step-Down The number of loops in the primaryand secondary coils of a transformer determines whether itincreases or decreases the voltage. If a transformer increasesvoltage, it is a step-up transformer. If a transformer decreasesvoltage, it is a step-down transformer. Both kinds of trans-formers are shown in Figure 26.

The primary coil of a step-uptransformer has fewer loopsthan the secondary coil. So thevoltage of the electric current in the secondary coil is higherthan the voltage of the electriccurrent in the primary coil.Therefore, voltage is increased.

The primary coil of a step-down transformer has moreloops than the secondary coil.So the voltage of the electriccurrent in the secondary coilis lower than the voltage ofthe electric current in the pri-mary coil. Therefore, voltageis decreased.


Figure 26 Transformers can either increase or decrease voltage.

Primary coil Secondary coil


Electrical Energy for Your Home The electric current thatprovides your home with electrical energy is usually transformedthree times before it reaches your home. Generators at thepower plants produce electric current with high voltage. Todecrease the loss of power that occurs during transmission overlong distance, the voltage is increased thousands of times witha step-up transformer. Of course, the voltage must be decreasedbefore it is distributed to households. Two different step-downtransformers are used before the electric current reaches con-sumers. Figure 27 shows how electric current is transformed onits way to your home.


1. How does a generator produce an electric current?

2. Explain why rotating either the coil or the magnet inducesan electric current in a generator.

3. Inferring Conclusions One reason why electric powerplants do not distribute electrical energy as direct cur-rent is that direct current cannot be transformed. Explainwhy not.

Figure 27 Electric current is transformedthree times before reaching your home.

REVIEW

Power plant, high voltage Step-up transformer Transmission lines, very high voltage

Distribution stationstep-down transformerLocal power lines,

lower voltage Home-supply (120 V) step-down transformer

1

2

3

NSTA

TOPIC: Electromagnetic InductionGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP445

Chapter Highlights

474

Visual UnderstandingELECTROMAGNETISM The two importantconcepts in electromagnetismwere discovered by Oerstedand Faraday. Figure 13on page 462 sum-marizes Oersted’swork, which showedthat an electric cur-rent can producea magnetic field.

SECTION 1 SECTION 2

Vocabularymagnet (p. 454)

poles (p. 454)

magnetic force (p. 455)

Section Notes

• All magnets have two poles.One pole will always point tothe north if allowed to rotatefreely, and it is called thenorth pole. The other pole iscalled the south pole.

• Like magnetic poles repeleach other; opposite mag-netic poles attract.

• All magnets are surroundedby a magnetic field. Theshape of that magnetic fieldcan be shown with magneticfield lines.

• A material is magnetic if itsdomains are aligned. Iron,nickel, and cobalt atomsgroup together in domains.

• Magnets can be classified asferromagnets, electromag-nets, temporary magnets,and permanent magnets. Amagnet can belong to morethan one group.

• Earth acts as if it has a bigbar magnet in its core.

• Compass needles and thenorth pole of magnets pointto Earth’s magnetic southpole—which is close toEarth’s geographic NorthPole.

• Auroras are most commonlyseen near Earth’s magneticpoles because Earth’s mag-netic fields bend inward atthe poles.

LabsMagnetic Mystery (p. 698)

Vocabularyelectromagnetism (p. 463)

solenoid (p. 463)

electromagnet (p. 464)

electric motor (p. 466)

Section Notes

• Oersted discovered that awire carrying an electric cur-rent produces a magneticfield.

• Electromagnetism is theinteraction between electric-ity and magnetism.

• A solenoid is a coil ofcurrent-carrying wire thatproduces a magnetic field.

• An electromagnet is a sole-noid with an iron core. Theelectromagnet has a strongermagnetic field than a sole-noid of the same size does.

• Increasing the current in asolenoid or an electromagnetincreases the magnetic field.

Skills Check

ELECTROMAGNETIC INDUCTION Faraday’s workshowed that a changing magnetic field caninduce an electriccurrent in a wire.His results aresummarized inFigure 21 onpage 469.



TOPIC: Magnetism sciLINKS NUMBER: HSTP430

TOPIC: Types of Magnets sciLINKS NUMBER: HSTP435

TOPIC: Electromagnetism sciLINKS NUMBER: HSTP440

TOPIC: Electromagnetic Induction sciLINKS NUMBER: HSTP445



KEYWORD: HSTEMG

475Electromagnetism

SECTION 3

• Increasing the number ofloops on a solenoid or anelectromagnet increases themagnetic field.

• A magnet can exert a forceon a wire carrying a current.

• In a doorbell, the magneticfield of a solenoid pulls aniron rod, and the iron rodstrikes the bell.

• The magnetic force betweena magnet and wires carryingan electric current makes anelectric motor turn.

• An electric motor convertselectrical energy into kineticenergy.

• A galvanometer measurescurrent by using the mag-netic force between an elec-tromagnet and a permanentmagnet.

LabsBuild a DC Motor (p. 700)

Vocabularyelectromagnetic induction (p. 469)

generator (p. 470)

transformer (p. 472)

Section Notes

• Faraday discovered that achanging magnetic field can create an electric currentin a wire. This is called elec-tromagnetic induction.

• Generators use electromag-netic induction to convertkinetic energy into electricalenergy.

• Kinetic energy can be sup-plied to a generator in differ-ent ways.

• Transformers increase ordecrease the voltage of analternating current usingelectromagnetic induction.

• A step-up transformerincreases the voltage of analternating current. Its pri-mary coil has fewer loopsthan its secondary coil.

• A step-down transformerdecreases the voltage of analternating current. Its pri-mary coil has more loopsthan its secondary coil.

LabsElectricity from Magnetism (p. 699)

SECTION 2




1. All magnets have two ? . (magneticforces or poles)

2. A(n) ? converts kinetic energy into electrical energy. (electric motor orgenerator)

3. ? occurs when an electric current isproduced by a changing magnetic field.(Electromagnetic induction or Magneticforce)

4. The interaction between electricity andmagnetism is called ? . (electromag-netism or electromagnetic induction)


Multiple Choice

5. The region around a magnet in whichmagnetic forces can act is called thea. magnetic field. c. pole.b. domain. d. solenoid.

6. An electric fan has an electric motorinside to change a. kinetic energy into electrical energy.b. thermal energy into electrical energy.c. electrical energy into thermal energy.d.electrical energy into kinetic energy.

7. The marked end of a compass needlealways points directly toa. Earth’s geographic South Pole.b. Earth’s geographic North Pole.c. a magnet’s south pole.d.a magnet’s north pole.

8. A device that increases the voltage of analternating current is called a(n)a. electric motor.b. galvanometer.c. step-up transformer.d. step-down transformer.

9. The magnetic field of a solenoid can beincreased bya. adding more loops.b. increasing the current.c. putting an iron core inside the coil to

make an electromagnet.d.All of the above

10. What do you end up with if you cut amagnet in half?a. one north-pole piece and one south-

pole pieceb. two unmagnetized piecesc. two pieces, each with a north pole and

a south poled. two north-pole pieces

Short Answer

11. Explain why auroras are seen mostly nearthe North and South Poles.

12. Compare the function of a generator withthe function of an electric motor.

13. Explain why some pieces of iron are moremagnetic than others.


Concept Mapping

14. Use the followingterms to create aconcept map:electromagnetism,electricity, magnetism,electromagneticinduction, generator,transformer.


15. You win a hand-powered flashlight as aprize in your school science fair. The flash-light has a clear plastic case so you canlook inside to see how it works. When you press the handle, a gray ring spinsbetween two coils of wire. The ends of thewire are connected to the light bulb. Sowhen you press the handle, the light bulbglows. Explain how an electric current isproduced to light the bulb. (Hint: Paperclips are attracted to the gray ring.)

16. Fire doors are doors that can slow thespread of fire from room to room whenthey are closed. In some buildings, firedoors are held open by electromagnets.The electromagnets are controlled by thebuilding’s fire alarm system. If a fire isdetected, the doors automatically shut.Explain why electromagnets are usedinstead of permanent magnets.


17. Study the solenoids and electromagnetsshown below. Rank them in order ofstrongest magnetic field to weakest mag-netic field. Explain your ranking.


a

b

c

d

Current = 2 A

Current = 2 A

Current = 4 A

Current = 4 A



ReadingCheck-up



Geomagnetic StormsOn March 13, 1989, a storm hit Montreal,Quebec. But this wasn’t an ordinary storm. Thiswas a geomagnetic storm that caused an elec-trical blackout. About 6 million people wentwithout electricity for 9 hours.

What Is a Geomagnetic Storm? To understand a geomagnetic storm, you mustfirst know a few things about the sun. By look-ing closely at the surface of the sun, scientistshave discovered that it has cycles of very violentactivity. Powerful eruptions called solar flaresoccur periodically, sending charged particlesoutward at almost the speed of light and withthe energy of millions of hydrogen bombs. Asparticles explode away from the solar surface,they create a solar wind of charged particlesthat travels several million kilometers per hourthrough space between the sun and the Earth.A geomagnetic storm occurs when the solarwind sweeps across Earth’s atmosphere, caus-ing a variety of disturbances.

Grids and PipelinesGeomagnetic storms happen frequently, espe-cially in the north. As the people of Quebecfound out in 1989, such storms can interferewith systems used to operate power grids. Theycan also cause heavy static in long-distanceradio reception and can affect the orbit of satel-lites. Geomagnetic storms can even cause cor-rosion in the metal of petroleum pipelines. Infact, scientists are not sure that they know of allthe systems and materials that are affected bygeomagnetic storms.

Knowledge Is the First Line ofDefenseSolar flares are not well understood and aredifficult to predict. There may be nothing thatcan be done to stop geomagnetic storms, butunderstanding them better is the first steptoward protecting valuable systems from aneruption’s effects. Scientists prepared severalsatellites to study the sun’s activity and solarflares in 2000 and 2001. By studying solareruptions, scientists think they can predict ageomagnetic storm 50 to 70 hours in advance.This could give industries affected by thesestorms time to protect their systems.

Solar Sails for Solar Wind Do research on solar flares and geomagneticstorms. Government agencies and universitieshave a number of programs, including satellites,to study and predict solar events. Create amodel or a poster to explain something youlearned from your research.

Solar flares on the sun can result ingeomagnetic storms here on Earth.


479

Think about whatit would be liketo peer inside

the human body tolocate a tumor, findtiny blockages in bloodvessels, or even identifydamage to the brain.Medical technologyknown as magneticresonance imaging(MRI) gives doctors aquick and painless wayto see and diagnosethese problems andmore.

MagneticImagesLike X rays, MRI creates pictures of a person’sinternal organs and skeleton. But MRI producesclearer pictures than X rays do, and MRI doesnot expose the body to the potentially harmfulradiation of X rays. Instead, MRI uses powerfulelectromagnets and radio waves to createimages.

The patient is placed in a large machine. Anelectric current in the electromagnet creates apowerful magnetic field around the patient.Because the human body is composed mostly offat and water, there are many hydrogen atoms inthe body. The magnetic field causes the nuclei ofthe hydrogen atoms to align in the direction ofthe magnetic field. Then another, weaker mag-netic signal is sent out to the cells. The energy inthis signal causes some hydrogen nuclei to changetheir position. As the signal's energy is absorbedand then released by the hydrogen nuclei, theMRI machine collects the signals and its com-puter converts the information into an image.

A DiagnosticDeviceMRI is particularly use-ful for locating smalltumors, revealing sub-tle changes in thebrain, pinpointingblockages in blood ves-sels, and showing dam-age to the spinal cord.This technology alsoallows doctors toobserve the function ofspecific body parts,such as the ears, heart,muscles, tendons, andblood vessels.

Researchers are experimenting with more-powerful magnets that work on other types ofatoms. This technology is known as magneticresonance spectroscopy (MRS). One currentuse of MRS is to monitor the effectiveness ofchemotherapy in cancer patients. Doctors ana-lyze MRS images to find chemical changesthat might indicate whether the therapy issuccessful.

Picture This You may be familiar with X rays, but pro-cedures like CAT or CT scans and MRI maybe new to you. Research the different imag-ing tools—including X-ray tomography, CT orCAT scans, and MRI—that doctors can use todiagnose and treat injuries and disease.Select one of the imaging processes andmake a model of how it works to demon-strate to the class. Be sure to include theprocedure's advantages and disadvantagesand the types of injuries or diseases forwhich it is used.

Magnets in Medicine

This color-enhanced MRI image ofa brain shows a tumor (tinted yel-low). The tumor was removed, andthe patient resumed a healthy life.


480 Chapter 19

Electronic Components . . . . . . . . 482


CommunicationTechnology . . . . . . . . . 488

Geology Connection . . 489Internet Connect . . . . 493

Computers . . . . . . . . . 494MathBreak . . . . . . . . .497Internet Connect . . . . 499

Chapter Review . . . . . . . . 502


LabBook . . . . . . . . . . . 702–705

ElectronicTechnologyElectronicTechnology

Electronic Traffic ControlIs this a photo of a futuristic town, seen from high in theair? Look more closely. Those pathways are not streets andhighways. They are tiny, complex electrical pathways on amicrochip, a device that controls the flow of electric cur-rent. Microchips are the basic building blocks of computersand other high-tech devices. In this chapter, you will learnhow electronic devices, such as computers, radios, and televisions, work and how circuit boards are made and electronic signals are produced.


1. What is an electronicdevice?

2. What are some electronicdevices used for commu-nication?

3. What are the parts of acomputer?


481

TALKING LONG DISTANCEUsing a telephone allows you tocommunicate with someone from adistance. In this activity, you’ll con-struct a model of a telephone.

Procedure

1. Thread one end of a piece ofstring through the hole in the bot-tom of one empty coffee can.

2. Tie a knot in the end of the stringinside the can. The knot should belarge enough to keep the string inplace. The rest of the string shouldbe coming out of the bottom ofthe can.

3. Repeat steps 1 and 2 with an-other can and the other end of the string.

4. Hold one can and have a class-mate hold the other. Walk awayfrom each other until the string ispulled fairly taut.

5. Speak into your can while yourclassmate holds the other can athis or her ear. Switch roles.

Analysis

6. In your ScienceLog, describe whatyou heard.

7. How is your apparatus similar to areal telephone? How is it different?

8. How are signals sent back andforth along the string?

9. Why do you think it was importantto pull the string taut?

Electronic TechnologyCopyright © by Holt, Rinehart and Winston. All rights reserved.

Section

1

circuit board diodesemiconductor transistordoping integrated circuit

Describe semiconductors andhow their conductivity can bemodified.

Identify diodes, transistors, andintegrated circuits as electroniccomponents.

Explain how integrated circuitshave influenced electronictechnology.

Compare vacuum tubes andtransistors.

Chapter 19482

Electronic ComponentsElectronic devices rely on electrical energy, but not in the sameway that appliances and machines do. Some machines can convert electrical energy into light, thermal, and mechanicalenergy in order to do work. Electronic devices use electricalenergy to transmit information.

Inside an Electronic DeviceA TV remote control is an example of an electronic device. Ittransmits information to a TV about volume levels and whatchannel to display. Have you ever looked inside of a TV remotecontrol? If so, you would have seen something similar toFigure 1. A remote control contains a circuit board, a collec-tion of hundreds of tiny circuits that supply electric currentto the various parts of an electronic device.

To change channels or adjust the volume on the TV, youpush buttons on the remote control. When you push abutton, a tiny bulb called a light-emitting diode (DIE OHD),or LED, sends information to the TV in the form ofinfrared light. The components of the circuit board yousee in Figure 1 control the electric current within theremote control in order to send the correct informa-tion to the TV. In this section you’ll learn about somecomponents of electronic devices and how they con-trol electric current.

Figure 1 Each part of a remote control has a role in transmitting information.


SemiconductorsMany electronic components are made from semiconductors(SEM i kuhn DUHK tuhrz). A semiconductor is a substance thatconducts an electric current better than an insulator but not aswell as a conductor. The use of semiconductors has resulted insome incredible advances in electronic technology.

How Do Semiconductors Work? The way a semiconductorconducts electric current is based on how its electrons arearranged. Silicon (Si) is a widely used semiconductor in elec-tronic technology. When silicon atoms bond, they share theirvalence electrons, as shown in Figure 2. Because all the valenceelectrons are shared, there are no electrons free to create muchelectric current in the semiconductor. So why are semicon-ductors like silicon used in electronic devices? Because theirconductivity can be modified.

Doping In order to modify the conductivity of a semicon-ductor, its arrangement of electrons must be altered. This isdone through doping (DOHP eeng), the process of replacing afew atoms of a semiconductor with a few atoms of another sub-stance that have a different number of valence electrons. Twotypes of doped semiconductors are shown in Figure 3.

Figure 2 Each silicon atomshares its four valence electronswith other silicon atoms.

Electronic Technology 483

Figure 3 Types of Doped Semiconductors

N-type semiconductor An atom of arsenic(As) has five electrons in its outermost energylevel. Replacing a silicon atom with an arsenicatom results in an “extra” electron.

P-type semiconductor An atom of gallium (Ga)has three electrons in its outermost energy level.Replacing a silicon atom with a gallium atomresults in a “hole” where an electron could be.

“Extra”electron

“Hole”


DiodesLayers of semiconductors can be put together like sandwichesto make electronic components. For example, joining one layerof an n-type semiconductor and one layer of a p-type semi-conductor creates a semiconductor diode, like the one shownin Figure 4. A diode is an electronic component that allowselectric current in only one direction.

Diodes in Circuits The way in which a diode works has todo with its semiconductor layers. Where the p-type and n-typelayers meet, some “extra” electrons move from the n-type layerto fill some “holes” in the p-type layer. This gives the p-typelayer a negative charge and the n-type layer a positive charge.If a diode is connected to a source of electrical energy so thatthe positive terminal is closest to the p-type layer, a currentis established. However, if the terminals are reversed so thatthe negative terminal is closest to the p-type layer, there willbe no current. Figure 5 illustrates how a diode works.

Chapter 19484

Figure 5 How a Diode Works

a b

+ + +

+ + +

+ +

+ +++

+ +

Electrons move from the negatively chargedp-type layer toward the positive terminal. Asa result, electrons from the n-type layer canmove to fill the newly created “holes” in thep-type layer, and a current is established.

Figure 4 This diodeis shown over fourtimes actual size.

Electrons in the negatively charged p-type layerare repelled by the negative terminal. No new“holes” are created, so no electrons can movefrom the n-type layer to the p-type layer. As aresult, there is no current.

Power plants supply electrical energy to homes by means of AC(alternating current). Many electronicsystems, however, such as radios,require DC (direct current). Becausediodes allow current in only one direction, they can convert AC topulses of DC. An AC adapter containsa diode.

Alternating current, whichperiodically changes direction,is supplied to the diode.

The diode blocks the currentin one direction, resulting inpulsed direct current.

Using Diodes to Change AC to DC

b

a

P-type N-type P-type N-type


TransistorsWhat do you get when you sandwich three layers of semi-conductors together? A transistor! A transistor is an electroniccomponent that can be used as an amplifier or as a switch.Transistors, such as the one shown in Figure 6, can be NPN orPNP transistors. An NPN transistor consists of one layer of ap-type semiconductor between two layers of an n-type semi-conductor. A PNP transistor consists of one layer of an n-typesemiconductor between two layers of a p-type semiconductor.When connected in a circuit, the transistor’s “legs” conductelectric current into and out of the transistor’s layers.

Transistors as Amplifiers To see how a transistor is used asan amplifier, look at the circuit shown in Figure 7. A micro-phone does not supply a large enough current to operate aloudspeaker. But if a transistor is used, the small electric cur-rent in the microphone side of the circuit can trigger a largerelectric current in the loudspeaker side of the circuit. The elec-tric current can be larger because of the large source of electricalenergy in the loudspeaker side of the circuit.

Figure 6 This transistor issmaller than a pencil eraser!


Figure 7 A Transistor as an Amplifier

Sound waves from your voiceenter the microphone. As aresult, a small electric currentis produced in the micro-phone side of the circuit.

A transistor allows thesmall electric current totrigger a larger electriccurrent that operates theloudspeaker.

The current in the loud-speaker is identical to thecurrent produced by themicrophone, except that ithas a larger amplitude.

Small electric current

Transistor

Amplified electric current

1 2 3


Transistors as Switches A transistor can also be used as anelectronic on-off switch in a circuit. When the manual switchin Figure 8 is closed, a small current is established in the leftside of the circuit. The small current causes the transistor toclose the right side of the circuit. As a result, a larger current,which operates a small motor, is established in the right sideof the circuit. Basically, you switch on a small current, andthe transistor switches on a larger current. If the manual switchis opened, there will no longer be a current in the left side ofthe circuit. As a result, the transistor will switch off the cur-rent that operates the motor. Circuits similar to the one inFigure 8 can be found in remote-controlled toy cars and inwindshield wipers.

Integrated Circuits Look at the electronic device shown inFigure 9. This is an integrated (IN tuh GRAYT ed) circuit, anentire circuit containing many transistors and other electroniccomponents formed on a single silicon chip. The componentsof the circuit are constructed on the silicon layer by dopingthe silicon at specific places.

Integrated circuits and circuit boards, such as the one inthe TV remote control at the beginning of this section, havehelped shrink electronic systems. Because several complete cir-cuits can fit into one integrated circuit, complicated electronicsystems can be made very small. In addition, integrated cir-cuit devices can operate at high speeds because the electriccharges traveling through them do not have to travel very far.

Figure 8 A Transistor as a Switch

Chapter 19486

When the manual switchcloses, a small current isestablished.

The transistor acts as a switch because a small current in thetransistor closes the right side of the circuit. A larger currentcan therefore operate the motor.

Motor

Transistor

1

2

Figure 9 This integrated circuitcontains thousands of electroniccomponents, yet its dimensionsare only about 1 3 cm!



1. Describe how p-type and n-type semiconductors are made.

2. Explain how a diode changes AC to DC.

3. What two purposes do transistors serve?

4. Comparing Concepts How might an electronic systemthat uses vacuum tubes be different from one that usesintegrated circuits?

REVIEW

Electronic Technology of Yesterday . . .

Before the invention of transistors and semiconductor diodes, electronicdevices used vacuum tubes, like the one shown here. Vacuum tubes canamplify electric current and convert AC to DC. However, vacuum tubesare much larger, give off more thermal energy, and don’t last as long astransistors and semiconductor diodes. Early radios were very bulkybecause they were made with vacuum tubes. Another reason theradios had to be so big was so that the vacuum tubes had space to give off thermal energy.

. . . and Today

Modern radios are built with transistorsand semiconductor diodes. Frequently, aradio comes with other features, such asa clock or a tape deck, all packaged in less space than a radio made withvacuum tubes. Modern electronic components have enabled electronicdevices to become much smaller andperform more functions.

NSTA

TOPIC: TransistorsGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP455


Section

2

telecommunicationsignalanalog signaldigital signal

Describe how signals transmitinformation.

Explain how a telephone works. Compare analog and digital

signals. Describe how radios and

televisions transmit information.

Figure 10 Combinations ofshort taps (dots) and longertaps (dashes) represent numbers and letters.

Chapter 19488

Communication TechnologyOne of the first electronic communication devices was the tele-graph, which was invented in the 1830s. Figure 10 shows thetelegraph key invented by Samuel Morse. The telegraph usedan electric current to send messages between two devices con-nected by wires. Telegraph operators sent messages in Morsecode by tapping the telegraph key to close an electric circuit,causing “clicks” at the recieving end of the telegraph. Althoughtelegraphs are not used much today, they served as the firstexample of telecommunication, the sending of informationacross long distances by electronic means. In this section you’lllearn about some electronic devices that are used forcommunication.

Communicating with SignalsElectronic communication devices transmit information byusing signals. A signal is something that represents informa-tion. A signal can be a command, a sound, or a series ofnumbers and letters. Often a signal travels better when con-tained in another form of energy, called a carrier. For exam-ple, in a telegraph, electric current is the carrier of the signalscreated by tapping the telegraph key. Two types of signalsthat carry information in electronic communication devicesare analog signals and digital signals.

International Morse Code

1 .----2 ..---3 ...--4 ....-5 .....6 -....7 --...8 ---..9 ----.0 -----

Q --.-R .-.S ...T -U ..-V ...-W .--X -..-Y -.--Z --..

G --.H ....I ..J .---K -.-L .-..M --N -.O ---P .--.

A .-B -...C -.-.D -..E .F ..-.

Write out a message to afriend using Morse code.

.... . .-.. .-.. ---H E L L O


Analog SignalsThe signals that carry the information through telephone linesare analog signals. An analog (AN uh LAHG) signal is a signalwhose properties, such as amplitude and frequency, can changecontinuously according to changes in the original informa-tion. For example, when you talk on the phone, the sound ofyour voice is converted into changing electric current in theform of a wave. This wave is an analog signal that is similarin frequency and amplitude to the original sound wave. Justremember that the analog signal is not a sound wave—it is awave of electric current.

Talking on the Phone Look at the telephone in Figure 11.The part you talk into is called the transmitter, and the partyou listen to is called the receiver. The transmitter convertsthe sound waves produced when you speak into the analogsignal that travels through phone wires to the receiver ofanother phone. The receiver converts the analog signal backinto the sound of your voice.


Figure 11 How a Telephone Works

Sound waves in the transmittercause a metal disk to vibrate.The vibrations are converted intoa changing electric current that iscarried by the telephone wires.

The analog signal, a changing electriccurrent, is sent over the phone wires.

The electric current is converted backinto a sound waveby the receiver. Thesound heard isalmost the same asthe sound that wasgenerated on theother end of the line.

a

b

c

A seismograph is a device geologistsuse to record earthquakes. A seismo-graph produces a seismogram—wavylines on paper that represent earth-quake waves. A seismogram is anexample of an analog signal. Thewaves on a seismogram are similarin amplitude and frequency to thewaves produced by an earthquake.As the earthquake changes in magni-tude, the lines change accordingly.



Analog Recording One way to reproduce sound is by stor-ing an analog signal of the sound wave. In vinyl records, theanalog signal is carved into a grooved plastic disk. The fre-quency and loudness of the sound are represented by the num-ber and depth of the contours carved into the grooved disk.

Playing a Record Figure 12 shows how a record player’s nee-dle, called a stylus (STIE luhs), creates vibrations in anelectromagnet. The vibrating electromagnet creates an electriccurrent that is used to produce sound. Although analog record-ing produces sound that is very similar to the original sound,it has some drawbacks. First, undesirable sounds are sometimesrecorded and are difficult to filter out. Also, because the sty-lus physically touches the record to play it, records can wearout, so the sound can be changed over time.

Digital SignalsA digital signal is a series of electric pulses that represents thedigits of binary (BIE neh ree) numbers. Binary means two. Aseries of digits, which are composed of only two numbers—1and 0—represent binary numbers. Each pulse in a digital sig-nal stands for a 1, and each missing pulse is a 0.

Digital Storage on a CD You’ve probably listened tothe digital sound from a compact disc, or CD.

Sound is recorded onto a CD by means of a digi-tal signal. A CD stores digital signals in a thinlayer of aluminum. As shown in Figure 13,the aluminum layer has a series of pits. Eachpit is a 0, and each nonpitted region, calleda land, is a 1.

Chapter 19490

Figure 12 As the stylus rides inthe record’s grooves, it causes anelectromagnet to vibrate.

ElectromagnetStylus

Electric current

PlasticAluminum

Figure 13 Pits and lands form a tight spiralfrom the center to the outer edge on a CD.They store information that can be convertedby a CD player into sound.

Label

Land

Protective coating

Pit


Digital Recording In a digital recording, the amplitude ofthe sound wave is sampled many times per second. From thesamples, numbers are generated that are equal to the ampli-tude of the sound at each instant. Figure 14 shows how thesesample values represent the original sound signal. These num-bers are then represented in binary as 1s and 0s and stored aspits and lands on a CD. Undesirable sample values can be fil-tered out, resulting in a cleaner sound.

The drawback to digital recording is that the sample valuesdon’t exactly match the original sound wave. To improve thereproduction of sound, a higher sampling rate can be used. Ahigher sampling rate means that there will be more samplevalues taken each second (narrower bars), and the resultingdigital sound will be closer to the original sound.

Playing a CD In a CD player, the CD spins around while alaser scans it from underneath. As shown in Figure 15, thedetector in a CD player receives light reflected from the sur-face of the CD. The detector converts the pattern of reflectedlight into a digital signal. The digital signal is changed intoan analog signal, which is used to generate a sound wave.Because only light touches the CD, the CD doesn’t wear outeven after it has been played many times.


A laser beam shines on the disc.

The patterns of reflectedlight are treated as a codeusing 1s and 0s.

The pattern of 1s and 0s isconverted into a sound wave.

Laser

Detector

Figure 15 Different sequences and sizes of pits and lands willregister different patterns of numbers that are converted intodifferent sounds.

a

b c

Figure 14 Each bar represents adigital sample of the soundwave.

Time

Ampl

itude


Radio and TelevisionWhen you turn on your radio or television, you can hear orsee programs broadcast from a radio or TV station that maybe many kilometers away. Radio and television use electro-magnetic waves. An electromagnetic wave is a wave that con-sists of changing electric and magnetic fields.

Radio Radio waves are one type of electromagnetic wave. Thebasic operation of a radio involves using radio waves to carrysignals that represent sound. As shown in Figure 16, radiowaves are transmitted by a radio tower, travel through the air,and are picked up by a radio antenna.

Figure 16 How Radio Works

Chapter 19492

Get tuned in! Turn to page 702in the LabBook, and build yourown radio-wave receiver.

A microphone creates an electric current that isan analog signal of the original sound wave.

A modulator combines the amplified analog signalwith radio waves that have a specific frequency.

A radio tower transmitsmodulated radio wavesthrough the air.

The antenna in a radio “tunedin” to the correct frequencyreceives the modulated radiowaves. The receiver removesthe radio waves from the analog signal.

The radio’s speakers convertthe analog signal, the electriccurrent, into sound.

1

2

3

4

5


Television The images you see on your television are pro-duced by beams of electrons projected onto a screen. Threebeams of electrons are produced within a cathode-ray tube, orCRT. The screen is coated with special fluorescent (FLOO uhRES uhnt) materials that glow when hit by electrons. Videosignals, which contain the information that produces an image,are carried by electromagnetic waves. Electromagnetic wavesalso carry the audio signals that produce sound from the speak-ers. Look at Figure 17 to learn how a color television works.

Figure 17 Images on a Color Television

1. How are analog signals different from digital signals?

2. Compare how a telephone and a radio tower transmitinformation.

3. Making Predictions How could a digital signal becorrupted?

Electronic circuits separate the videosignal into separate signals for eachof three electron beams. The beams, one for each primary color of light (red, green,and blue), strike the screen in varying strengths determined by the video signal.

Three fluorescent materials (each corresponding to an electronbeam) are arranged in stripes or dotson the screen. The electron beams sweep the screen to activate the flourescent materials. These materials then emit colored light that is viewed as a picture.

Video signals transmitted from a TV stationare received by the antenna of a TV receiver.

REVIEW

Use a magnifying lens to lookat a television screen. Howare the fluorescent materialsarranged? Hold the lens atvarious distances from thescreen. What effects do yousee? How does the screen’schanging picture affect whatyou see?

1

2

3


NSTA

TOPIC: Telephone Technology, TelevisionTechnology



Section

3

computermicroprocessorhardwaresoftwareInternet

List the basic functions of acomputer.

Identify the main components ofcomputer hardware.

Describe what computer soft-ware allows a computer to do.

Describe how the Internetworks.

Figure 19The Functions of a Computer

Chapter 19494

ComputersDid you use a computer to wake up this morning? You mightthink of a computer as something you use to send e-mail orsurf the Net, but computers are around you all the time.Computers are in automobiles, VCRs, and telephones. Even analarm clock is a computer! An alarm clock, like the one inFigure 18, lets you program the time you want to wake up,and will wake you up at that time.

What Is a Computer?A computer is an electronic device that performs tasks by pro-cessing and storing information. A computer performs a taskwhen it is given a command and has the instructions neces-sary to carry out that command. Computers do not operateby themselves, or “think.”

Basic Functions The basic functions a computer performs areshown in Figure 19. The information you give to a computeris called input. Setting your alarm clock is a type of input. Toperform a task, a computer processes the input, changing it toa desirable form. Processing could mean adding a list of num-bers, executing a drawing, or even moving a piece of equip-ment. Input doesn’t have to be processed immediately; it canalso be stored until it is needed. Computers store informationin their memory. For example, your alarm clock stores the timeyou want to wake up. It can then process this stored infor-mation by going off when it is the programmed time. Outputis the final result of the task performed by the computer. What’sthe output of an alarm clock? The sound that wakes you up!

Figure 18 Believe it or not, thisalarm clock is a computer!

Input

Output

Storage

Processing


Historic DevelopmentsYour pocket calculator is a simple example of a computer. Butcomputers weren’t always so small and efficient. The first com-puters were massive systems consisting of large pieces of elec-tronic equipment that could fill up an entire room.

The First Computers The first general-purpose computer isshown in Figure 20. This monstrous collection of equipmentis the ENIAC (Electronic Numerical Integrator and Computer),developed in 1946 by the U.S. Army. The ENIAC consisted ofthousands of vacuum tubes and, as a result, produced a lot ofexcess thermal energy. It was also extremely expensive to buildand maintain.

Modern Computers With the invention of transistors andintegrated circuits, the size of computers could be greatlyreduced. Computers today use microprocessors, like the one shown in Figure 21. A microprocessor is an integratedcircuit that contains many of a computer’s capabilities ona single silicon chip. The first commercially availablemicroprocessor contained only 4,800 transistors, butmicroprocessors made today may contain more than 3 million transistors. As a result, computers can nowbe made so small and lightweight that we can carrythem around like a notebook!

Figure 21 This microprocessoris about 4 4 cm.

Figure 20 Fast for its time, theENIAC could add 5,000 numbersper second.


When the ENIAC was built,transistors and integrated cir-cuits did not exist. Instead, itused 18,000 vacuum tubes,filled a 10 15.25 m room,had a mass of more than23,500 kg, and used as muchelectrical energy as 150 ordi-nary light bulbs!


Computer HardwareFor each function of a computer, there is a corresponding partof the computer where each function occurs. Hardware refersto the parts or equipment that make up a computer. As youread about each piece of hardware, refer to Figure 22.

Input Devices Instructions given to a computer are calledinput. An input device is the piece of hardware that feeds infor-mation to the computer. You can enter information into acomputer using a keyboard, a mouse, a scanner, a digitizingpad and pen—even your own voice!

Central Processing Unit A computer performs tasks withinan area called the central processing unit, or CPU. In a personalcomputer, the CPU is a microprocessor. Input goes throughthe CPU for immediate processing or for storage in memory.The CPU is where the computer does calculations, solves prob-lems, and executes the instructions given to it.

Chapter 19496

Figure 22 Computer Hardware

Microphone

Monitor

Speaker

Modem port

Keyboard Mouse

CPU

RAM

ROM

Hard disk

Floppy drive

CD-ROM drive


Memory Information can be stored in the computer’s mem-ory until it is needed. Hard disks inside a computer andfloppy disks or CD-ROMs inserted into a computer have mem-ory to store information. Two other types of memory areROM (read-only memory) and RAM (random-access memory).

ROM is permanent. It handles functions such as computerstart-up, maintenance, and hardware management. ROM nor-mally cannot be added to or changed, and it cannot be lostwhen the computer is turned off. On the other hand, RAMis temporary. It stores information only while that informationis being used. RAM is sometimes called working memory.Large amounts of RAM allow more information to be input,which makes for a more powerful computer.

Output Devices Once a computer performs a task, it showsthe results on an output device. Monitors, printers, and speakersystems are all examples of output devices.

Modems One piece of computer hardware that serves as aninput device as well as an output device is a modem. Modemsallow computers to communicate. One computer can inputinformation into another computer over a telephone line, aslong as each computer has its own modem. As a result, modemspermit computers to “talk” with other computers.


Floppy disk

Scanner

CD-ROM

Printer

Digitizing pad and pen

Computer MemoryComputers operate usingbinary numbers. Each digit ina binary number is called abit. Computers store andprocess information in chunkscalled bytes. A byte is eightbits of information in a com-puter’s memory. A kilobyte is1,024 bytes, and a gigabyte is1,073,741,824 bytes.

1. Some computer memory isexpressed in gigabytes.How many bits can a 1.5gigabyte hard disk store?

2. Suppose you download a document from theInternet that uses 25 kilo-bytes of memory. Howmany of those documentscould you fit on a diskcontaining 1 gigabyte of memory?

MATH BREAK


Computer SoftwareComputers need a set of instructions before they can performany given task. Software is a set of instructions, or commands,that tells a computer what to do. A computer program is anexample of software.

Kinds of Software Software can be classified into two cat-egories: operating system software and application software.Operating system software manages basic operations requiredby the computer and supervises all interactions between soft-ware and hardware. It interprets commands from the inputdevice, such as locating programming instructions on a harddisk to be loaded into memory.

Application software contains instructions ordering thecomputer to operate a utility, such as a word processor, spread-sheet, or even a computer game. The pages in this book werecreated using a variety of application software! Some examplesof application software are shown in Figure 23.

Chapter 19498

Figure 23 Computer softwareallows a computer to perform allkinds of tasks, such as word pro-cessing, video games, interactivetutoring, and graphics.


The Internet—A Global NetworkThanks to modems and computer software, it is possible toconnect many computers and allow them to communicatewith one another. That’s what the Internet is—a huge com-puter network consisting of millions of computers that can allshare information with one another.

How the Internet Works Computers can connect toone another on the Internet by using modems to dialinto an Internet Service Provider, or ISP. A home com-puter connects to an ISP over a normal phone line. Aschool, business, or other group can have a LocalArea Network (LAN) that connects to an ISP usingone phone line. As depicted in Figure 24, ISPsare connected globally by satellite. And that’show computers go global!


1. Using the terms input, output, processing, and memory,explain how you use a pocket calculator to add numbers.

2. What is the difference between hardware and software?

3. Analyzing Relationships Could something like the Internetexist without modems and telephone lines? Explain.

REVIEW

Figure 24 Through a series ofconnections like this, every computeron the Internet can share information.

NSTA

TOPIC: Computer Technology, InternetGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP470, HSTP475


Chapter Highlights

Chapter 19500

SECTION 1 SECTION 2

Vocabularycircuit board (p. 482)

semiconductor (p. 483)

doping (p. 483)

diode (p. 484)

transistor (p. 485)

integrated circuit (p. 486)

Section Notes

• Electronic devices use elec-trical energy to transmitinformation.

• Many electronic componentsare made of semiconductors.Two types of semiconductorsresult from a process calleddoping. They are n-type andp-type semiconductors.

• The two types of semicon-ductors can be sandwichedtogether to produce diodesand transistors.

• Diodes allow electric currentin only one direction.

• Transistors can be used asamplifiers or as switches.

• Integrated circuits can con-tain many electronic compo-nents. They allow electronicsystems to be smaller.

Vocabularytelecommunication (p. 488)

signal (p. 488)

analog signal (p. 489)

digital signal (p. 490)

Section Notes

• Electronic devices use signals to transmit information. Thesignals are usually containedin another form of energy,such as radio waves or electric current.

• The properties of analog sig-nals change continuouslyaccording to changes in theoriginal signal. Telephonesuse analog signals.

• A digital signal is a series ofelectrical pulses that repre-sents the digits of binarynumbers. CD players usedigital signals.

Skills CheckVisual UnderstandingDIODES Sandwiching an n-type semiconductorand a p-type semiconductor together producesa diode. Charges can pass through a diode inonly one direction.

TRANSMITTING SIGNALS BY RADIO Electronic devices transmitinformation through signals.Look at Figure 16 on page 492to see how electromagneticwaves can transmit radiosignals.

COMPUTERS In order for acomputer to perform a task, itmust be given information.Look at the diagram on page494 to learn about the steps a computer takes to perform various tasks.

+ + +

+ + +

+


501Electronic Technology

SECTION 3

• Sound can be recorded digi-tally or as an analog signal.

• Radio and television rely onelectromagnetic waves.

• In radio, signals that repre-sent sound are combinedwith radio waves and sentthrough the air. Radios canpick up the radio waves andconvert them back to soundwaves.

• A color television image isproduced by three electronbeams that scan the screen ofa cathode-ray tube, or CRT.Fluorescent materials on thescreen glow to create thepicture.

LabsTune In! (p. 702)

Vocabularycomputer (p. 494)

microprocessor (p. 495)

hardware (p. 496)

software (p. 498)

Internet (p. 499)

Section Notes

• The basic functions of a com-puter involve input, process-ing, memory, and output. Acomputer cannot perform atask without a set ofcommands.

• The first computers were verylarge and could not performmany tasks.

• Because microprocessors con-tain many computer capabil-ities on a single chip, com-puters have been reduced in size.

• Computer hardware refers tothe parts or the equipmentthat make up a computer.

• Computer software is a set ofinstructions or commandsthat tells a computer what to do.

• Modems allow millions ofcomputers to connect withone another and share infor-mation on the Internet.

SECTION 2


TOPIC: Transistors sciLINKS NUMBER: HSTP455

TOPIC: Telephone Technology sciLINKS NUMBER: HSTP460

TOPIC: Television Technology sciLINKS NUMBER: HSTP465

TOPIC: Computer Technology sciLINKS NUMBER: HSTP470

TOPIC: Internet sciLINKS NUMBER: HSTP475



KEYWORD: HSTELT




1. semiconductor/doping

2. transistor/diode

3. signal/telecommunication

4. analog signal/digital signal

5. computer/microprocessor

6. hardware/software


Multiple Choice

7. All electronic devices transmit informa-tion usinga. signals.b. electromagnetic

waves.c. radio waves.d.modems.

8. Semiconductors are used to makea. transistors. b. integrated circuits.c. diodes.d.All of the above

9. Which of the following is an example of atelecommunication device?a. vacuum tubeb. telephonec. radiod.Both (b) and (c)

10. A monitor, printer, and speaker are examples ofa. input devices. c. computers.b. memory. d.output devices.

11. Record players play sounds that wererecorded in the form ofa. digital signals.b. electric current.c. analog signals.d. radio waves.

12. Memory in a computer that is permanentand cannot be added to is calleda. RAM.b. ROM.c. CPU.d.None of the above

13. Cathode-ray tubes are used ina. telephones.b. telegraphs.c. televisions.d. radios.

Short Answer

14. How is an electronic device different froma machine that uses electrical energy?

15. How does a diode allow current to flow inone direction?

16. In one or two sentences, describe how aTV works.

17. Give three examples of how computers are used in your everyday life.

18. Explain the advantages that transistors have over vacuum tubes.


Concept Mapping

19. Use the followingterms to create aconcept map:electronic devices,radio waves, electriccurrent, signals, information.


20. Your friend is preparing an oral report onthe history of radio and finds the photo-graph shown below. “Why is this radio sohuge?” he asks you. Using what you knowabout electronic devices, how do youexplain the size of this vintage radio?

21. Using what you know about the differ-ences between analog and digital signals,explain how the sound from a recordplayer is different from the sound from a CD player.

22. What do Morse code and digital signalshave in common?

23. Computers can process a lot of informa-tion, but they cannot think. Explain whythis is true.

24. Based on what you learned in the chapter,how do you think an automatic garagedoor opener works?


Look at the diagram below, and answer thequestions that follow.

25. What purpose does the transistor serve inthis situation?

26. How does the current in the left side ofthe circuit compare with the current inthe right side of the circuit?

27. How does the sound from the speakercompare with the sound from the guitar?


Inputfromguitar Output

fromspeaker

Transistor



ReadingCheck-up


504

Do you ever lis-ten to yourfavorite music

on headphones? Manypeople like to useheadphones whilethey exercise. Terrific!But doctors believethat this habit may beputting people’s hear-ing at risk.

The BloodBrain DrainAerobic exercise,including walking,jogging, skating,dancing, and competi-tive sports, is an important part of a healthylifestyle. However, when you exercise, moreblood is sent to your arms and legs than issent to your ears. The inner ear is more easilydamaged when the blood flow is lowered.Once the cells of the inner ear are damaged,they cannot be replaced. A study in Swedenshowed that hearing loss doubles when loudnoise and aerobic exercise are combined!

How Loud Is Too Loud?The federal Occupational Safety and HealthAdministration (OSHA) requires hearingprotection for workers exposed to 95 decibelsfor 4 hours. A lawn mower emits 95 decibels.If workers are exposed to 100 decibels for 3 hours, they must wear hearing protection.People generally listen to headphones at levelsbetween 90 and 115 decibels.

Why So Loud? Most people turn the volume up as they con-tinue to listen to music because their ears adaptto the volume. However, permanent hearing

loss can occur at wellbelow painful or evenuncomfortable levels.Another concern isthat hearing loss isoften gradual, startingat high frequencies.The loss goes unno-ticed until the dam-age is quite extensive.Generally, more prob-lems occur whennoise is louder, lastslonger, or occursfrequently.

What to Do How can you protect

your hearing and still use those headphones?Keep the volume of your headphones as low aspossible, and try not to raise the volume once itis set. Then always remember this: If a person 1 m away has to shout in order for you to hear,the volume is too high. However, this test doesnot work for headphones with muffs that fitaround the ear. The volume is probably toohigh if your hearing is dulled after youremove your headphones. This usually goesaway quickly, but it may become permanentif you keep the volume high.

Sound It Out Obtain a sound meter, and survey thesound levels around your school. Measure the levels at dances and other noisy loca-tions. Report your findings to your class, and discuss ways to lower your exposure to loud sounds. You may just save some-one’s hearing!

Listening Lower

How high should the volume be whenlistening to music on headphones?


505

“There Will ComeSoft Rains”

by Ray Bradbury

Ticktock, seven o'clock, time to get up,time to get up, seven o'clock. The voiceclock in the living room sends out the

wake-up message, gently calling to the familyto get up and begin their new day.

It is August 4, 2026, in Allandale, California.The house is attractive, in an attractive neigh-borhood, just right for a mother, father, twochildren, and a dog. And it is state of the art:automatic kitchen, extremely sensitive fire-detection and fire-protection systems, walls thatlook like walls but become video displayscreens—everything a family could want.

A few minutes after the wake-up call, theautomatic stove in the kitchen begins the fam-ily breakfast—toast, eggs (sunny side up), andbacon. While the breakfast is cooking, the voicein the kitchen ceiling lists the reminders for theday: a birthday, an anniversary, the bills thatare due.

About an hour after the wake-up message,the ceiling voice speaks again, this time toremind anyone listening that it is time to go toschool. A soft rain is falling outside, so theweather box by the front door suggests thatraincoats are necessary today.

But something has happened. No familysounds come from the house. The house goeson talking to itself and carrying on its routine asif it were keeping itself company. Why doesn'tanyone answer? Find out when you read RayBradbury's “There Will Come Soft Rains” in theHolt Anthology of Science Fiction.


T I M E L I N E

U N I T Waves, Sound,and Light

Unit 7506

7hen you hearthe word

waves, you probablythink of waves in theocean. But waves thatyou encounter everyday have a much big-ger effect on your lifethan do water waves!In this unit, you willlearn about differenttypes of waves, howwaves behave andinteract, and howsound energy andlight energy travel inwaves. This timelineshows some eventsand discoveries thathave occurred through-out history as scien-tists have sought tolearn more about theenergy of waves.

WAround

1600Italian astronomer and physicist Galileo Galilei

attempts to calculate the speed of light byusing lanterns and shutters. He writes that the

speed is “extraordinarily rapid.”

1929American astronomer

Edwin Hubble uses theDoppler effect of lightto determine that theuniverse is expanding.

1960The first working laser

is demonstrated.

1971Hungarian physicist

Dennis Gabor wins theNobel Prize in Physics

for his invention ofholography, themethod used to make holograms.

1947The Diary of Anne Frankis published. The bookis an edited version of

the diary kept by aJewish teenager while

in hiding during World War II.

PH01PETML07007PFirst laser


1711The tuning fork—an instrument

that produces a single-frequencynote—is invented by English

trumpeter John Shore.

1801British scientist Thomas

Young is the first to provide experimental data showing

that light behaves as a wave.

1905Physicist Albert Einstein

suggests that lightsometimes behaves

as a particle.

1983The exact speed of

light is determined tobe 299,792,458 m/s.

1997British pilot Andy Green

drives a jet-powered car at 341m/s, making him the first personto travel faster than the speed of

sound on land.

1704Sir Isaac Newton publishes hisbook Optiks, which contains histheories about light and color.

1984A “mouse” is firstused on personal

computers.

Waves, Sound, and Light 507

1903The popularity of an early moviecalled The Great Train Robberyleads to the establishment of permanent movie theaters.


508 Chapter 20

The Nature of Waves . . 510Astronomy

Connection . . . . . . 512MathBreak . . . . . . . . . 513Internet Connect . . . . 515

Properties of Waves . . 516QuickLab . . . . . . . . . . 518MathBreak . . . . . . . . . 519Internet Connect . . . . 519

Wave Interactions . . . . 520Apply . . . . . . . . . . . . . 523Internet Connect . . . . 525

Chapter Review . . . . . . . . . 528


LabBook . . . . . . . . . . . 706–709


1. What is a wave?2. What properties do all

waves have?3. What can happen when

waves interact?

The Energy of WavesThe Energyof Waves


509

ENERGETIC WAVESIn this activity, you will observe themovement of a wave. Then you willdetermine the source of the wave’senergy.

Procedure

1. Tie one end of a piece of rope tothe back of a chair.

2. Hold the other end in one hand,and stand away from the chair sothat the rope is almost straight butis not pulled tight.

3. Move the rope up and downquickly to create a single wave.Repeat this step several times.Record your observations in yourScienceLog.

Analysis

4. Which direction does the wavemove?

5. How does the movement of therope compare with the movementof the wave?

6. Where does the energy of thewave come from? Make an infer-ence using direct evidence.

Catch the Wave!A surfer takes advantage of a wave’s energy to catchan exciting ride. The ocean wave that this surferis riding is just one type of wave that you mayencounter. You probably are very familiar withwater waves, but did you know that waves are alsoresponsible for light, sound, and even earthquakes?From music to television, waves play an importantrole in your life every day. In this chapter, youwill learn about the properties of waves and howwaves interact with each other and everythingaround them.

The Energy of WavesCopyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 20510

The Nature of WavesImagine that your family has just returned home from a dayat the beach. You had fun, but you are hungry from playingin the ocean under a hot sun. You put some leftover pizza inthe microwave for dinner, and you turn on the radio. Justthen, the phone rings. It’s your best friend calling to find outif you’ve done your math homework yet.

In the events described above, how many different waveswere present? Believe it or not, at least five can be identified!Can you name them? Here’s a hint: A wave is any disturbancethat transmits energy through matter or space. Okay, here arethe answers: water waves in the ocean; microwaves inside themicrowave oven; light waves from the sun; radio waves trans-mitted to the radio; and sound waves from the radio, tele-phone, and voices. Don’t worry if you didn’t get very many.You will be able to name them all after you read this section.

Waves Carry EnergyEnergy can be carried away from its source by a wave. However,the material through which the wave travels does not movewith the energy. For example, sound waves often travel throughair, but the air does not travel with the sound. If air were totravel with sound, you would feel a rush of air every time youheard the phone ring! Figure 1 illustrates how waves carryenergy but not matter.

Figure 1 Waves on a pond move toward the shore, but the waterand the leaf floating on the surface do not move with the wave.

Wave motion

Section

1

wave transverse wavemedium longitudinal wave

Describe how waves transferenergy without transferring matter.

Distinguish between waves thatrequire a medium and wavesthat do not.

Explain the difference betweentransverse and longitudinalwaves.


As a wave travels, it uses its energy to do work on every-thing in its path. For example, the waves in a pond do workon the water to make it move up and down. The waves alsodo work on anything floating on the water’s surface—for exam-ple, boats and ducks bob up and down with waves.

Energy Transfer Through a Medium Some waves transferenergy by the vibration of particles in a medium. A mediumis a substance through which a wave can travel. A mediumcan be a solid, a liquid, or a gas. The plural of medium is media.

When a particle vibrates (moves back and forth, as inFigure 2), it can pass its energy to a particle next to it. As aresult, the second particle will vibrate in a way similar to thefirst particle. In this way, energy is transmitted through amedium.

Sound waves require a medium. Sound energy travels bythe vibration of particles in liquids, solids, and gases. If thereare no particles to vibrate, no sound is possible. For example,if you put an alarm clock inside a jar and remove all the airfrom the jar to create a vacuum, you will not be able to hearthe alarm.

Other waves that require a medium include ocean waves,which travel through water, and waves on guitar and cellostrings. Waves that require a medium are called mechanicalwaves. Figure 3 shows the effect of another mechanical wave.

Figure 2 A vibration is one com-plete back-and-forth motion ofan object.

Figure 3 Seismic waves travelthrough the ground. The 1964earthquake in Alaska changedthe features of this area.

The Energy of Waves 511Copyright © by Holt, Rinehart and Winston. All rights reserved.


Energy Transfer Without a Medium Some waves can trans-fer energy without traveling through a medium. Visible lightis an example of a wave that doesn’t require a medium.Other examples include microwaves produced by microwaveovens, TV and radio signals, and X rays used by dentistsand doctors. Waves that do not require a medium are calledelectromagnetic waves.

Although electromagnetic waves do not require a medium,they can travel through substances such as air, water, and glass.However, they travel fastest through empty space. Light fromthe sun is a type of electromagnetic wave. Figure 4 shows thatlight waves from the sun can travel through both space andmatter to support life on Earth.

Chapter 20512

Figure 4 Light waves from the sun travel more than 100 millionkilometers through nearly empty space, then more than 300 kmthrough the atmosphere, and then another 10 m through water tosupport life in and around a coral reef.

Self-CheckHow do mechanical waves differ from electromag-netic waves? (See page 724 to check your answer.)


Light waves from some stars andgalaxies travel distances so great thatthey can be expressed only in light-years. A light-year is the distance thatlight travels in a year. Some of thelight waves from these stars havetraveled billions of light-years beforereaching Earth. This means that thelight that we see today from somedistant stars left the star’s surfacebefore the Earth was formed.

You can see distantobjects in space usingelectromagnetic waves.

Turn to page 530 to learn how.


Types of WavesWaves can be classified based on the direction in which theparticles of the medium vibrate compared with the directionin which the waves travel. The two main types of waves aretransverse waves and longitudinal (LAHN juh TOOD nuhl)waves. In certain conditions, a transverse wave and a longi-tudinal wave can combine to form another type of wave, calleda surface wave.

Transverse Waves Waves in which the particles vibrate withan up-and-down motion are called transverse waves. Transversemeans “moving across.” The particles in a transverse wavemove across, or perpendicular to, the direction that the waveis traveling. To be perpendicular means to be “at right angles.”Try the MathBreak to practice identifying perpendicular lines.

A wave moving on a rope is an example of a transversewave. In Figure 5, you can see that the points along the ropevibrate perpendicular to the direction the wave is traveling.The highest point of a transverse wave is called a crest, andthe lowest point between each crest is called a trough. Althoughelectromagnetic waves do not travel by vibrating particles ina medium, all electromagnetic waves are classified as trans-verse waves.

The Energy of Waves 513

Figure 5 A wave on a rope isa transverse wave because theparticles of the medium vibrateperpendicular to the directionthe wave moves.

Perpendicular LinesIf the angle between twolines is 90°, the lines are saidto be perpendicular. The fig-ure below shows a set ofperpendicular lines.

Look at the objects aroundyou. Identify five objects withperpendicular lines or edgesand five objects that do nothave perpendicular lines.Sketch these objects in yourScienceLog.

MATH BREAK

Crests

Troughs

90°

The wave travels to the right.

The points alongthe rope vibrateup and down.

Longitudinal Waves In a longitudinal wave, the particles ofthe medium vibrate back and forth along the path that thewave travels. You can create a longitudinal wave on a spring,as shown in Figure 6.

When you push on the end of the spring, the coils of thespring are crowded together. A section of a longitudinal wavewhere the particles are crowded together is called a compression.When you pull back on the end of the spring, the coils are lesscrowded than normal. A section where the particles are lesscrowded than normal is called a rarefaction (RER uh FAK shuhn).

Compressions and rarefactions travel along a longitudinalwave much in the way the crests and troughs of a transversewave move from one end to the other, as shown in Figure 7.

Figure 6 Pushing a springback and forth creates alongitudinal wave.

Figure 7 The compressions of alongitudinal wave are like thecrests of a transverse wave, andthe rarefactions are like troughs.

Rarefactions

Compressions


The coils of the spring move back andforth but do not travel with the wave.

The wave moves forward on the spring.


A sound wave is an example of a longitudinal wave. Soundwaves travel by compressions and rarefactions of air particles.Figure 8 shows how a vibrating drumhead creates these com-pressions and rarefactions.

Combinations of Waves When waves occur at or near theboundary between two media, a transverse wave and a longitu-dinal wave can combine to form a surface wave. An example isshown in Figure 9. Surface waves look like transverse waves, butthe particles of the medium in a surface wave move in circlesrather than up and down. The particles move forward at thecrest of each wave and move backward at the trough. The arrowsin Figure 9 show the movement of particles in a surface wave.

1. Describe how transverse waves differ from longitudinalwaves.

2. Why can’t you cause a floating leaf to move to the edgeof a pond by throwing stones behind it?

3. Explain why supernova explosions in space can be seenbut not heard on Earth.

4. Applying Concepts Sometimes people at a sports eventdo “the wave.” Do you think this is a real example of awave? Why or why not?


REVIEW

Figure 8 Sound energy iscarried away from a drumin a longitudinal wave.

Figure 9 Ocean waves are surface waves becausethey travel at the water’s surface, where the watermeets the air. A floating bottle shows the motionof particles in a surface wave.

When the drumhead moves outafter being hit, a compression iscreated in the air particles.

When the drumhead movesback in, a rarefaction is created.

Wave motion

NSTA

TOPIC: The Nature of Waves, Types ofWaves


Properties of WavesImagine that you are canoeing on a lake. You decide to stoppaddling for a while and relax in the sunshine. The breezemakes small waves on the water. These waves are short and close together, and they have little effect on the canoe.Then a speedboat roars past you. The speedboat creates tall,

widely spaced waves that cause your canoe torock wildly. So much for relaxation!

Waves have properties that areuseful for description and com-

parison. In this example, youcould compare properties suchas the height of the waves and the distance between thewaves. In this section, youwill learn about the proper-ties of waves and how to

measure them.

AmplitudeIf you tie one end of a rope to the back of a chair, you can cre-ate waves by moving the other end up and down. If you movethe rope a small distance, you will make a short wave. If youmove the rope a greater distance, you will make a tall wave.

The property of waves that is related to the height of awave is known as amplitude. The amplitude of a wave is themaximum distance the wave vibrates from its rest position. Therest position is where the particles of a medium stay whenthere are no disturbances. The larger the amplitude is, the tallerthe wave is. Figure 10 shows how the amplitude of a transversewave is measured.

Figure 10 The amplitude of a transverse wave is meas-ured from the rest position tothe crest or to the trough ofthe wave.

Chapter 20516

Rest position

Amplitude

Section

2

amplitude frequencywavelength wave speed

Identify and describe four wave properties.

Explain how amplitude andfrequency are related to the energy of a wave.


Larger Amplitude Means More Energy When using a ropeto make waves, you have to work harder to create a wave witha large amplitude than to create one with a small amplitude.This is because it takes more energy to move the rope fartherfrom its rest position. Therefore, a wave with a large amplitudecarries more energy than a wave with a small amplitude, asshown in Figure 11.

WavelengthAnother property of waves is wavelength. A wavelength is thedistance between any two adjacent crests or compressions ina series of waves. The distance between two adjacent troughsor rarefactions is also a wavelength. In fact, the wavelengthcan be measured from any point on one wave to the corre-sponding point on the next wave. All of the measurementswill be equal, as shown in Figure 12.

Figure 12 Wavelengthsmeasured from any two cor-responding points are thesame for a given wave.

Longitudinal wave


Wavelength

Wavelength

WavelengthTransverse wave

Small amplitude = low energy Large amplitude = high energy

Wavelength

Figure 11 The amplitudeof a wave depends on theamount of energy.


Chapter 20518

Wavelength

Springy Waves

1. Hold a coiled spring toyon the floor between youand a classmate so thatthe spring is straight. Thisis the rest position.

2. Move one end of thespring from side to side ata constant rate. The num-ber of times you move it ina complete cycle (back andforth) each second is thefrequency.

3. Keeping the frequency thesame, increase the ampli-tude. What did you have to do? How did the changein amplitude affect thewavelength?

4. Now shake the spring backand forth about twice asfast (to double the fre-quency). What happens tothe wavelength?

5. Record your observationsand answers in yourScienceLog.

Spring into action! Find thespeed of waves on a spring toy. Turn to page 708 of the LabBook.

Wavelength

FrequencyThink about making rope waves again. The number of wavesthat you can make in 1 second depends on how quickly youmove the rope. If you move the rope slowly, you make onlya small number of waves each second. If you move it quickly,you make a large number of waves. The number of waves pro-duced in a given amount of time is the frequency of the wave.

Measuring Frequency You can measure frequency by count-ing either the number of crests or the number of troughs thatpass a point in a certain amount of time. If you were meas-uring the frequency of a longitudinal wave, you would countthe number of compressions or rarefactions. Frequency is usu-ally expressed in hertz (Hz). For waves, one hertz equals onewave per second (1 Hz 1/s). The frequency of a wave isrelated to its wavelength, as shown in Figure 13.

Higher Frequency Means More Energy It takes moreenergy to vibrate a rope quickly than to vibrate a rope slowly.If the amplitudes are equal, high-frequency waves carry moreenergy than low-frequency waves. In Figure 13, the top wavecarries more energy than the bottom wave.

Because frequency and wavelength are so closely related,you can also relate the amount of energy carried by a waveto the wavelength. In general, a wave with a short wavelengthcarries more energy than a wave with a long wavelength.

Figure 13 At a given speed, the higher the frequency is, the shorter the wavelength.


1. Draw a transverse wave, and identify its amplitude andwavelength.

2. What is the speed (v) of a wave that has a wavelength ()of 2 m and a frequency (f ) of 6 Hz?

3. Inferring Conclusions Compare the amplitudes and fre-quencies of the two types of waves discussed at the begin-ning of this section, and infer which type of wave carriedthe most energy. Explain your answer.


Figure 14 To calculate wavespeed, multiply the wavelengthby the number of waves thatpass in 1 second (frequency).

Wave CalculationsThe equation for wave speedcan be rearranged to deter-mine wavelength () orfrequency (f ).

vf f v

You can determine the wavelength of a wave with aspeed of 20 m/s and a frequency of 4 Hz like this:

vf

20 m/s 4 Hz

20sm 14

s

5 m

Now It’s Your Turn1. What is the frequency of a

wave if it has a speed of12 cm/s and a wavelengthof 3 cm?

2. A wave has a frequency of 5 Hz and a wave speedof 18 m/s. What is itswavelength?

MATH BREAK

Wave 3 Wave 2 Wave 1

0.5 m

0.5 m f 3 Hz (3/s)v 0.5 m 3 Hz 1.5 m/s

Wave SpeedAnother property of waves is wave speed—the speed at whicha wave travels. Speed is the distance traveled over time, sowave speed can be found by measuring the distance a singlecrest or compression travels in a given amount of time.

The speed of a wave depends on the medium in which thewave is traveling. For example, the wave speed of sound in airis about 340 m/s, but the wave speed of sound in steel is about5,200 m/s.

Calculating Wave Speed Wave speed can be calculated usingwavelength and frequency. The relationship between wavespeed (v), wavelength (, the Greek letter lambda), and fre-quency (f ) is expressed in the following equation:

v f

You can see in Figure 14 how this equation can be used todetermine wave speed. Try the MathBreak to practice usingthis equation.

REVIEW

NSTA

TOPIC: Properties of WavesGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP485


Chapter 20520

Wave InteractionsImagine that you wake up early one morning before the sunhas risen and go outside. You look up and notice that a fullmoon is high in the sky, and the stars are twinkling brilliantly,as shown in Figure 15. The sky is so clear you can find con-stellations (groupings of stars), such as the Big Dipper andCassiopeia, and planets, such as Venus and Mars.

All stars, including the sun, produce light. But planets andthe moon do not produce light. So why do they shine sobrightly? Light from the sun reflects off the planets and themoon. Reflection is one of the wave interactions that you willlearn about in this section.

ReflectionReflection occurs when a wave bounces backafter striking a barrier. All waves—includingwater, sound, and light waves—can bereflected. The reflection of water waves isshown in Figure 16. Reflected sound wavesare called echoes, and light waves reflectingoff an object allow you to see that object.For example, light waves from the sun arereflected when they strike the surface of themoon. These reflected waves allow us toenjoy moonlit nights.

Figure 16 These water waves are reflecting off the side of the container.

Figure 15 A waveinteraction is responsi-ble for this beautifulmorning scene.

Section

3

reflection interferencerefraction standing wavediffraction resonance

Describe reflection, refraction,diffraction, and interference.

Compare destructive interferencewith constructive interference.

Describe resonance, and giveexamples.


RefractionTry this simple experiment: place a pencil in a half-filled glassof water. Now look at the pencil from the side. The pencilappears to be broken into two pieces! But when you take thepencil out of the water, it is perfectly fine.

What you observed in this experiment was the result ofthe refraction of light waves. Refraction is the bending of awave as it passes at an angle from one medium to another.

Remember that the speed of a wave varies depending onthe medium in which the wave istraveling. So when a wave moves fromone medium to another, the wave’sspeed changes. When a wave entersa new medium at an angle, the partof the wave that enters first beginstraveling at a different speed from therest of the wave. This causes the waveto bend, as shown in Figure 17.

DiffractionSuppose you are walking down a city street and you hearmusic. The sound seems to be coming from around the cor-ner, but you cannot see who is playing the music because thebuilding on the corner blocks your view. Why is it that soundwaves travel around a corner better than light waves do?

Most of the time, waves travel in straight lines. For exam-ple, a beam of light from a flashlight is fairly straight. But insome circumstances, waves curve or bend when they reach theedge of an object. The bending of waves around a barrier orthrough an opening is known as diffraction.


Self-CheckWill a light wave refract if it enters a new mediumperpendicular to the surface? Explain. (See page 724to check your answer.)

Wave crests

Figure 17 Light waves passing at anangle into a new medium—such aswater—are refracted because the speedof the waves changes.

Light waves diffract aroundcorners of buildings muchless than sound waves.Imagine what would happenif light waves diffractedaround corners much morethan sound waves. Write aparagraph describing howthis would change what yousee and hear as you walkaround your neighborhood.


Figure 18 Diffraction of Waves

The amount of diffraction a wave experiences depends onits wavelength and the size of the barrier or opening the waveencounters, as shown in Figure 18. You can hear music aroundthe corner of a building because sound waves have long wave-lengths and are able to diffract around corners. However, youcannot see who is playing the music because the wavelengthsof light waves are much smaller than the building, so light isnot diffracted very much.

InterferenceYou know that all matter has volume. Therefore,objects cannot occupy the same space at the sametime. But because waves are energy and not matter,more than one wave can exist in the same place atthe same time. In fact, two waves can meet, share thesame space, and pass through each other! When twoor more waves share the same space, they overlap.The result of two or more waves overlapping is calledinterference. Figure 19 shows one situation wherewaves occupy the same space.

522

Figure 19 When sound waves fromseveral instruments combine throughinterference, the result is a wave witha larger amplitude, which means alouder sound.

a b

When the barrier or opening is the same size as oris smaller than the wavelength of an approachingwave, the amount of diffraction is large.

If the barrier or opening is larger than the wave-length of the wave, there is only a small amountof diffraction.


Constructive Interference Increases Amplitude Constructiveinterference occurs when the crests of one wave overlap thecrests of another wave or waves. The troughs of the waves alsooverlap. An example of constructive interference is shown inFigure 20. When waves combine in this way, the result is a newwave with higher crests and deeper troughs than the originalwaves. In other words, the resulting wave has a larger ampli-tude than the original waves had.

Destructive Interference Decreases Amplitude Destructiveinterference occurs when the crests of one wave and the troughsof another wave overlap. The resulting wave has a smalleramplitude than the original waves had. What do you thinkhappens when the waves involved in destructive interferencehave the same amplitude? Find out in Figure 21.


Figure 20 When waves combineby constructive interference, theresulting wave has an amplitudethat is larger than those of theoriginal waves. After the wavesinterfere, they continue travelingin their original directions.

Figure 21 When two waves withthe same amplitude combine bydestructive interference, they can-cel each other out. This is calledtotal destructive interference.

Waves approaching Waves overlapping Waves continuing

Waves approaching Waves overlapping Waves continuing

Sound Waves in Movie TheatersMovie theaters use large screens and several speakers to makeyour moviegoing experience exciting. Theater designers knowthat increasing the amplitude of sound waves increases thevolume of the sound. In terms of interference, how do youthink the positioning of the speakers adds to the excitement?

Speakers

Speakers


Interference Can Create Standing WavesIf you tie one end of a rope to the back of achair and move the other end up and down,the waves you create travel down the rope andare reflected back. If you move the rope at cer-tain frequencies, the rope appears to vibrate inloops, as shown in Figure 22. The loops resultfrom the interference between the wave you cre-ated and the reflected wave. The resulting waveis called a standing wave. A standing wave is awave that forms a stationary pattern in whichportions of the wave are at the rest position dueto total destructive interference and other por-tions have a large amplitude due to construc-tive interference. However, it only looks as if thewave is standing still. In reality, waves are trav-eling in both directions. Standing waves can beformed with transverse waves, as shown here,as well as with longitudinal waves.

One Object Causes Another to Vibrate During ResonanceAs shown above, standing waves can occur at more than onefrequency. The frequencies at which standing waves are pro-duced are called resonant frequencies. When an object vibrat-ing at or near the resonant frequency of a second object causes

the second object to vibrate, resonance occurs. A reso-nating object absorbs energy from the vibrating

object and therefore vibrates, too. An example ofresonance is shown in Figure 23.

Figure 22 When you move arope at certain frequencies, youcan create different standingwaves.

Figure 23 A marimba pro-duces notes through theresonance of air columns.

Chapter 20524

a

b

c

d

The marimba bars arestruck with a mallet, causing the bars to vibrate.

The vibrating barscause the air in thecolumns to vibrate.

The lengths of the columns have beenadjusted so that the resonant frequency of theair column matches the frequency of the bar.

The air column resonates with the bar,increasing the amplitude of the vibrationsto produce a loud note.

Destructive interference

Constructive interference


The Tacoma Narrows Bridge Resonance was partially respon-sible for the destruction of the Tacoma Narrows Bridge, inWashington. The bridge opened in July 1940 and soon earnedthe nickname Galloping Gertie because of its wavelike motions.These motions were created by wind that blew across the bridge.The wind caused vibrations that were close to a resonant fre-quency of the bridge. Because the bridge was in resonance, itabsorbed a large amount of energy from the wind, which causedit to vibrate with a large amplitude.

On November 7, 1940, a supporting cable slipped, and thebridge began to twist. The twisting of the bridge, combinedwith high winds, further increased the amplitude of the bridge’smotion. Within hours, the amplitude became so great that thebridge collapsed, as shown in Figure 24. Luckily, all the peo-ple on the bridge that day were able to escape before it crashedinto the river below.

1. Name two wave interactions that can occur when a waveencounters a barrier.

2. Describe what happens when a wave is refracted.

3. Inferring Relationships Sometimes when music is playedloudly, you can feel your body shake. Explain what is happening in terms of resonance.


REVIEW

Figure 24 The twisting motionthat led to the destruction of thebridge was partially caused byresonance.

Resonance caused the col-lapse of a bridge nearManchester, England, in1831. Cavalry troopsmarched across the bridgein rhythm with its resonantfrequency. This caused thebridge to vibrate with alarge amplitude and even-tually to fall. Since thattime, all troops are orderedto “break step” when theycross a bridge.

NSTA

TOPIC: Interactions of WavesGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP495


Chapter Highlights

Chapter 20526

SECTION 1 SECTION 2

Vocabularywave (p. 510)

medium (p. 511)

transverse wave (p. 513)

longitudinal wave (p. 514)

Section Notes

• A wave is a disturbance thattransmits energy.

• A medium is a substancethrough which a wave cantravel. The particles of amedium do not travel withthe wave.

• Waves that require a mediumare called mechanical waves.Waves that do not require amedium are calledelectromagnetic waves.

• Particles in a transverse wavevibrate perpendicular to thedirection the wave travels.

• Particles in a longitudinalwave vibrate back and forthin the same direction thatthe wave travels.

• Transverse and longitudinalwaves can combine to formsurface waves.

Vocabularyamplitude (p. 516)

wavelength (p. 517)

frequency (p. 518)

wave speed (p. 519)

Section Notes

• Amplitude is the maximumdistance the particles in awave vibrate from their restposition. Large-amplitudewaves carry more energythan small-amplitude waves.

• Wavelength is the distancebetween two adjacent crests(or compressions) of a wave.

• Frequency is the number ofwaves that pass a given pointin a given amount of time.High-frequency waves carrymore energy than low-frequency waves.

Skills CheckMath ConceptsWAVE-SPEED CALCULATIONS The relationshipbetween wave speed (v), wavelength (), andfrequency (f ) is expressed by the equation:

For example, if a wave has a wavelength of 1 mand a frequency of 6 Hz (6/s), the wave speed iscalculated as follows:

Visual UnderstandingTRANSVERSE AND LONGITUDINAL WAVESTwo common types of waves are transversewaves (shown below) and longitudinal waves.Study Figure 5 on page 513 and Figure 6 onpage 514 to review the differences betweenthese two types of waves.

v f

v 1 m 6 Hz 1 m 6/sv 6 m/s


SECTION 3

• Wave speed is the speed atwhich a wave travels. Wavespeed can be calculated bymultiplying the wavelengthby the wave’s frequency.

LabsWave Energy and Speed (p. 706)

Wave Speed, Frequency, andWavelength (p. 708)

Vocabularyreflection (p. 520)

refraction (p. 521)

diffraction (p. 521)

interference (p. 522)

standing wave (p. 524)

resonance (p. 524)

Section Notes

• Waves bounce back afterstriking a barrier duringreflection.

• Refraction is the bending of a wave when it passes at anangle from one medium toanother.

• Waves bend around barriersor through openings duringdiffraction. The amount ofdiffraction depends on thewavelength of the waves andthe size of the barrier oropening.

• The result of two or morewaves overlapping is calledinterference.

• Amplitude increases duringconstructive interference anddecreases during destructiveinterference.

• Standing waves are waves inwhich portions of the wavedo not move and other por-tions move with a largeamplitude.

• Resonance occurs when avibrating object causesanother object to vibrate at one of its resonant frequencies.

SECTION 2


TOPIC: The Nature of Waves sciLINKS NUMBER: HSTP480

TOPIC: Properties of Waves sciLINKS NUMBER: HSTP485

TOPIC: Types of Waves sciLINKS NUMBER: HSTP490

TOPIC: Interactions of Waves sciLINKS NUMBER: HSTP495



KEYWORD: HSTWAV

527The Energy of WavesCopyright © by Holt, Rinehart and Winston. All rights reserved.



1. longitudinal wave/transverse wave

2. frequency/wave speed

3. wavelength/amplitude

4. reflection/refraction

5. constructive interference/destructive interference


Multiple Choice

6. As the wavelength increases, the frequencya. decreases.b. increases.c. remains the same.d. increases, then decreases.

7. Which wave interaction explains whysound waves can be heard around corners?a. reflection c. diffractionb. refraction d. interference

8. Refraction occurs when a wave enters anew medium at an angle becausea. the frequency changes.b. the amplitude changes.c. the wave speed changes.d. None of the above

9. The speed of a wave with a frequency of 2 Hz (2/s), an amplitude of 3 m, and awavelength of 10 m isa. 0.2 m/s. c. 12 m/s.b. 5 m/s. d. 20 m/s.

10. Waves transfera. matter. c. particles.b. energy. d. water.

11. A wave that is a combination of longitu-dinal and transverse waves is aa. sound wave. c. rope wave.b. light wave. d. surface wave.

12. The wave property that is related to theheight of a wave is thea. wavelength. c. frequency.b. amplitude. d. wave speed.

13. During constructive interference,a. the amplitude increases.b. the frequency decreases.c. the wave speed increases.d. All of the above

14. Waves that don’t require a medium area. longitudinal waves.b. electromagnetic waves.c. surface waves.d. mechanical waves.

Short Answer

15. Draw a transverse and a longitudinalwave. Label a crest, a trough, a compres-sion, a rarefaction, and wavelengths. Alsolabel the amplitude on the transversewave.

16. What is the relationship between fre-quency, wave speed, and wavelength?

17. Explain how two waves can cancel eachother out.


Concept Mapping

18. Use the followingterms to create a concept map: wave,refraction, transversewave, longitudinalwave, wavelength,wave speed,diffraction.


19. After you set up stereo speakers in yourschool’s music room, you notice that incertain areas of the room the sound fromthe speakers is very loud and in otherareas the sound is very soft. Explain howinterference causes this.

20. You have lost the paddles for the canoeyou rented, and the canoe has drifted tothe center of the pond. You need to getthe canoe back to shore, but you do notwant to get wet by swimming in thepond. Your friend on the shore wants tothrow rocks behind the canoe to createwaves that will push the canoe towardshore. Will this solution work? Why orwhy not?

21. Some opera singers have voices so power-ful they can break crystal glasses! To dothis, they sing one note very loudly andhold it for a long time. The walls of theglass move back and forth until the glassshatters. Explain how this happens interms of resonance.

MATH IN SCIENCE

22. A fisherman in a rowboat notices that onewave crest passes his fishing line every 5 seconds. He estimates the distancebetween the crests to be 2 m and esti-mates the crests of the waves to be 0.4 mabove the troughs. Using these data,determine the amplitude and wave speedof the waves. Remember that wave speedis calculated with the formula v f.


23. Rank the waves below from highestenergy to lowest energy, and explain yourreasoning.

a

b

c




ReadingCheck-up


530

The Ultimate Telescope

The largest telescopes in theworld don’t depend on visi-ble light, lenses, or mirrors.

Instead, they collect radio wavesfrom the far reaches of outerspace. One radio telescope, calledthe Very Large Array (VLA), islocated in a remote desert in New Mexico.

From Radio Waves toComputer ImagesObjects in space give off radiowaves that radio telescopes collect.A bowl-shaped dish called a reflec-tor focuses the radio waves onto asmall radio antenna hung over thecenter of the dish. The antennaconverts the waves into electric sig-nals. The signals are relayed to a radio receiver,where they are amplified and recorded on tapethat can be read by a computer. The computercombines the signals to create an image of thesource of the radio waves.

A Marvel at “Seeing”Radio telescopes have some distinct advantagesover optical telescopes. They can “see” objectsthat are as far as 13 billion light-years away.They can even detect objects that don’t releaseany light at all. Radio telescopes can be used in any kind of weather, can receive signalsthrough atmospheric pollution, and can evenpenetrate the cosmic dust and gas clouds thatoccupy vast areas of space. However, radio tele-scopes must be large in order to be accurate.

Telescope TeamworkThe VLA is an array of 27 separate radio tele-scopes mounted on railroad tracks and elec-tronically linked by computers. Each of the

27 reflectors is 25 m in diameter. When theyoperate together, they work like a single tele-scope with a diameter of 47 km! Using theVLA, astronomers have been able to exploredistant galaxies, pulsars, quasars, and possibleblack holes.

A system of telescopes even larger thanthe VLA has been used. In the Very LongBaseline Array (VLBA), radio telescopes in dif-ferent parts of the world all work together. Theresult is a telescope that is almost as large asthe Earth itself!

What Do They See? Find out about some of the objects “seen” bythe VLA, such as pulsars, quasars, and possibleblack holes. Prepare a report or create a modelof one of the objects, and make a presentationto your class. Use diagrams and photographs tomake your presentation more interesting.

Only a few of the 27 radio telescopes of theVLA, near Datil, New Mexico, can be seen inthis photograph.



Sounds of Silence

531

It’s morning on the African savanna. Suddenly,without a sound, a family of elephants stopseating and begins to move off. At the samemoment, about 6 km away, other members ofthe same family move off in a direction thatwill reunite them with the first group. How didthe groups know when it was time to go?

Do You Hear What I Hear?Elephants do much of their communicating byinfrasound. This is sound energy with a fre-quency too low to be heard by humans. Theseinfrasonic conversations take place throughdeep, soft rumblings produced by the animals.Though humans can’t hear the sounds, ele-phants as far as 10 km away respond quickly tothe messages.

Because scientists couldn’t hear the ele-phant “conversations,” they couldn’t understandhow the animals coordinated their activities. Ofcourse, the elephants, which have superb low-frequency hearing, heard the messages clearly.It turns out that much elephant behavior isaffected by infrasonic messages. For instance,one kind of rumble from a mother to her calftells the calf it is all right to nurse. Anotherrumble, from the group’s leader, is the “time tomove on” message. Still another infrasonicmessage may be sent to other elephant groupsin the area, warning them of danger.

Radio CollarsOnce scientists learned about elephants’ infra-sonic abilities, they devised ways to study thesounds. Researchers developed radio collars forindividual animals to wear. The collars are con-nected to a computer that helps researchersidentify which elephant sent the message. Thecollars also record the messages. This informa-tion helps scientists understand both the mes-sages and the social organization of the group.

Let’s TalkElephants have developed several ways to “talk”to each other. For example, they greet eachother by touching trunks and tusks. And ele-phants have as many as 25 vocal calls, includ-ing the familiar bellowing trumpet call (a signof great excitement). In other situations, theyuse chemical signals.

Recently, researchers recording elephantcommunications found that when elephantsvocalize their low-frequency sounds, they createseismic waves. Elephant messages sent bythese underground energy waves may be feltmore than 8 km away. Clearly, there is a lotmore to elephant conversations than meets the ear!

On Your Own Elephants are very intelligent and highlysociable. Find out more about the complexsocial structure of elephant groups. Why is itimportant for scientists to understand how ele-phants communicate with each other? How canthat understanding help elephants?

Two elephants greeting each other


532 Chapter 21

Sound Under the SeaLook at these dolphins swimming swiftly and silentlythrough their watery world. Wait a minute—swiftly? Yes.Silently? No way! Dolphins use sound to communicate. In fact, each dolphin has a special whistle that it uses toidentify itself. Dolphins also use sound to locate their foodand find their way through murky water. In this chapter,you’ll learn more about the properties and the interactionsof sound waves. You’ll also learn how sound is used tolocate objects.


1. How does sound travelfrom one place toanother?

2. What determines a sound’spitch and loudness?

3. What can happen whensound waves interact witheach other?

The Nature of SoundThe Nature of Sound

What Is Sound?. . . . . . 534QuickLab. . . . . . . . . . . 534Biology Connection . . 535AstronomyConnection . . . . . . . . 536


Properties of Sound. . . 539MathBreak . . . . . . . . . 540Biology Connection . . 541QuickLab. . . . . . . . . . . 543Internet Connect . . . . 544

Interactions of Sound Waves . . . . . . . . . . . . 545Apply . . . . . . . . . . . . . 547Internet Connect . . . . 551

Sound Quality . . . . . . 552Environment

Connection . . . . . . . 555Internet Connect . . . . 555

Chapter Review . . . . . . . . . 558


LabBook . . . . . . . . . . .710–715


A HOMEMADE GUITARIn this chapter, you will learn aboutsound. You can start by making yourown guitar. It won’t sound as goodas a real guitar, but it will help youexplore the nature of sound.

Procedure

1. Stretch a rubber bandlengthwise around an empty shoebox. Gently pluck the rubber band.In your ScienceLog, describe whatyou hear.

2. Stretch another rubber band of a different thickness around thebox. Pluck both rubber bands.Describe the difference in thesounds.

3. Put a pencil across the center ofthe box and under the rubberbands, and pluck again. Comparethis sound with the sound youheard before the pencil was used.

4. Move the pencil closer to one endof the shoe box. Pluck on bothsides of the pencil. Describe the differences in the sounds you hear.

Analysis

5. How did the thicknesses of therubber bands affect the sound?

6. In steps 3 and 4, you changed thelength of the rubber bands. What is the relationship between thelength of the rubber band and thesound that you hear?

533The Nature of SoundCopyright © by Holt, Rinehart and Winston. All rights reserved.

Good Vibrations

1. Gently strike a tuning forkon a rubber eraser. Watchthe prongs, and listen for asound. Describe what yousee and hear.

2. Lightly touch the fork withyour fingers. What do youfeel?

3. Grasp the prongs of thefork firmly with your hand.What happens to thesound?

4. Strike the tuning fork onthe stopper again, and dipthe prongs in a cup ofwater. Describe what hap-pens to the water.


Section

1

wavemediumouter earmiddle earinner ear

Describe how sound is causedby vibrations.

Explain how sound is transmit-ted through a medium.

Explain how the human earworks, and identify its parts.

Chapter 21534

What Is Sound?Think about all the sounds you hear every day. Indoors, youmight hear people talking, the radio blaring, or dishes clat-tering in the kitchen sink. Outdoors, you might hear birdssinging, cars driving by, or a mosquito buzzing in your ear.That’s a lot of different sounds! In this section, you’ll exploresome common characteristics of the different sounds you hear.

Sound Is Produced by VibrationsAs different as they are, all sounds have some things in com-mon. One characteristic of sound is that it is created by vibra-tions. A vibration is the complete back-and-forth motion of anobject. Figure 1 shows an example of how sound is created byvibrations.

Figure 1 Sounds from a Stereo Speaker

As the speaker cone moves forward, it pushes the air particlesin front of it closer together, creating a region of higher densityand pressure called a compression.

As the speaker cone moves backward, air particles close to thecone become less crowded, creating a region of lower densityand pressure called a rarefaction.

Every time the cone vibrates, compression and rarefaction areformed. As the compressions and rarefactions travel away fromthe speaker, sound is transmitted through the air.

a

b

c



The vibrations that produce yourvoice are made inside your throat.When you speak, laugh, or sing, yourlungs force air up your windpipe,causing your vocal cords to vibrate.

Sound Travels as Longitudinal Waves A wave is a distur-bance that transmits energy through matter or space. In a lon-gitudinal wave, particles vibrate back and forth along the paththat the wave travels. Longitudinal (LAHN juh TOOD nuhl) wavesconsist of compressions and rarefactions. Sound is transmittedthrough the vibrations and collisions of particles of matter, suchas air particles. Because the particles vibrate back and forth alongthe paths that sound travels, sound travels as longitudinal waves.

Sound waves travel in all directions away from their sourceas illustrated in Figure 2. However, air or other matter does nottravel with the sound waves. The particles of air only vibrateback and forth in place. If air did travel with sound, wind gustsfrom music speakers would blow you over at a school dance!

Creating Sound Vs. Detecting Sound

Think about this situation for a minute. When a tree falls andhits the ground, the tree and the ground vibrate. These vibra-tions create compressions and rarefactions in the surroundingair. So, yes, there would be a sound!

Making sound is separate from detecting sound. Thefact that no one heard the tree fall doesn’t mean thatthere wasn’t a sound. A sound was created—it justwasn’t detected.

Figure 2 You can’t actually seesound waves, but they can berepresented by spheres thatspread out in all directions.

Have you heard this riddle before?If a tree falls in the forest and no one is around

to hear it, does the tree make a sound?

CompressionRarefaction



The moon has no atmosphere, sothere is no air through which soundcan travel. The astronauts whowalked on the moon had to useradios to talk to each other evenwhen they were standing side byside. Radio waves could travelbetween the astronauts becausethey are electromagnetic waves,which don’t require a medium. Theradio speakers were inside the astro-nauts’ helmets, which were filledwith air for the astronauts to breathe.

Sound Waves Require a MediumAnother characteristic of sound is that allsound waves require a medium. A medium isa substance through which a wave can travel.In the example of a falling tree on the previ-ous page, the medium is air. Most of thesounds that you hear travel through air at leastpart of the time. But sound waves can alsotravel through other materials, such as water,glass, and metal, as shown in Figure 3.

What would happen if a tree fell in a vac-uum? No sound would be created because in avacuum, there are no air particles to vibrate.Sound cannot travel in a vacuum. This helpsto explain the effect described in Figure 4. Soundmust travel through air or some other mediumto reach your ears and be detected.

How You Detect SoundImagine you are watching a suspenseful movie. Just before adoor is opened, the background music becomes louder. Youknow that there is something scary behind that door! Nowimagine watching the same scene without the sound. It’s hardto figure out what’s going on without sound to help you under-stand what you see. Your ears play an important role in thisunderstanding. On the next page, you will see how your earsconvert sound waves into electrical signals, which are thensent to your brain for interpretation.

Chapter 21536

Figure 3 You can still hear traffic soundswhen you are in a car because sound wavescan travel through the glass windows andmetal body of the car.

Figure 4 Tubing is connected to a pump thatis removing air from the jar. As the air isremoved, the ringing alarm clock gets quieterand quieter.


The Nature of Sound 537

How the Human Ear Works

Pinna

Ear canal

HammerAnvil Stirrup

Eardrum

Cochlea

In the middle ear, threebones—the hammer, anvil,and stirrup—act as leversto increase the size of the vibrations.

The inner ear is wherevibrations created bysound are changed intoelectrical signals for thebrain to interpret.

Sound waves vibrate the eardrum—a lightly stretched membrane that isthe entrance to the middle ear.

The vibration of theeardrum makes thehammer vibrate, whichin turn makes the anviland stirrup vibrate.

The stirrup vibrates theoval window—the entranceto the inner ear. The vibrations of the oval

window create waves in theliquid inside the cochlea.

Movement of theliquid causes tinyhair cells insidethe cochlea tobend.

The bending of the hair cellsstimulates nerves,which send electrical signalsto the brain.

b ca The outer ear acts as a funnel forsound waves. The pinna collectssound waves and directs them intothe ear canal.

1

2

3

4

56


Hearing Loss and Deafness The many parts of the earmust work together for you to hear sounds. If any part of theear is damaged or does not work properly, hearing loss or deaf-ness may result.

One of the most common types of hearing loss is calledtinnitus (ti NIE tuhs), which results from long-term exposureto loud sounds. Loud sounds can cause damage to the haircells and nerve endings in the cochlea. Damage to the cochleaor any part of the inner ear usually results in permanent hear-ing loss.

People who have tinnitus often complain about hearing aringing in their ears. They also have difficulties understand-ing other people and hearing the difference between wordsthat sound very similar. Tinnitus can affect people of any age.Fortunately, tinnitus can be prevented. Figure 5 shows someways that you can protect yourself from hearing loss.

Turning your radio down willprevent hearing loss, especiallywhen you use headphones.

Wearing ear protection whileworking with machinery blocksout some of the sounds thatcan injure your ears.

Figure 5 Reducing exposure to loud sounds will protect your ears.

1. Describe how a bell produces sound.

2. Explain why a person at a rock concert will not feel gustsof wind coming out of the speakers.

3. Name the three main parts of the ear, and briefly explainthe function of each part.

4. Inferring Conclusions If a meteorite crashed on the moon,would you be able to hear it on Earth? Why or why not?

Chapter 21538

REVIEW

Could a dinosaur have played a horn? Check it out on page 560.

NSTA

TOPIC: What Is Sound?, The EarGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP505, HSTP510


Section

2

pitch Doppler effectinfrasonic loudnessultrasonic decibel

Compare the speed of sound indifferent media.

Explain how frequency and pitchare related.

Describe the Doppler effect, andgive examples of it.

Explain how amplitude andloudness are related.

Properties of SoundImagine you are swimming in a neigh-borhood pool. You hear many dif-ferent sounds as you float on thewater. Some are high, like thelaughter of small children, andsome are low, like the voicesof men. Some sounds areloud, like the BOING ofthe diving board, andsome are soft, like thesound of water lappingon the sides of the pool.The differences betweenthe sounds—how highor low and how loud orsoft they are—dependon the properties of thesound waves. In this sec-tion, you will learn aboutproperties of sound.

The Speed of Sound Depends on the MediumIf two people at the other end of the pool shout at you at thesame time, will you hear one person’s voice before the other?No—the sounds of their voices will reach you at the sametime. The time it takes for the sounds to reach you does notdepend on who shouted or how loudly the person shouted.The speed of sound depends only on the medium throughwhich the sound is traveling. Assuming that your head is abovewater, the sounds of the voices traveled through air to yourears and therefore traveled at the same speed.

Speed Changes When the Medium Changes The speed ofsound through any medium is constant if the properties ofthe medium do not change. The chart at left shows the speedof sound in different media. If the properties of a mediumchange, the speed of sound through that medium will change.On the next page, you will explore how a change in oneproperty—temperature—affects the speed of sound through air.


Speed of Sound in Different Media at 20°C

Medium

AirHeliumWaterSea waterWood (oak)GlassSteel

Speed (m/s)

3431,0051,4821,5223,8504,5405,200


The Speed of Sound Depends on Temperature In 1947,American pilot Chuck Yeager became the first person to travelfaster than the speed of sound. But he was flying at a speedof only 293 m/s! If the speed of sound in air is 343 m/s (asshown in the chart on the previous page), how did Yeager flyfaster than the speed of sound? The answer has to do withthe temperature of the air.

In general, the cooler the medium, the slower the speed ofsound. This happens because particles in cool materials moveslower than particles in warmer materials. When the particlesmove slower, they transmit energy more slowly. Therefore,sound travels more slowly in cold air than in hot air.

Chuck Yeager flew at 12,000 m above sea level. At thatheight the temperature of the air is so low that the speed ofsound is only 290 m/s. So when he flew at 293 m/s, he wasflying 3 m/s faster than the speed of sound.

Pitch Depends on FrequencyThink about the guitar you made at the beginning of thischapter. You used two rubber bands of different thicknessesas strings. You probably noticed that the thicker rubber bandmade a lower sound than the thinner rubber band made.How low or high you perceive a sound to be is the pitch ofthat sound.

The pitch of a sound is determined by the frequency ofthe sound wave, as shown in Figure 6. The frequency of a waveis the number of waves produced in a given time. Frequencyis expressed in hertz (Hz), where 1 Hz 1 wave per second.

Figure 6 The longer tuning fork vibrates at a lower frequency.Therefore, it creates a sound with a lower pitch.

Chapter 21540

Speed of SoundThe speed of sound dependson the medium throughwhich sound is traveling andthe medium’s temperature.Sound travels at 343 m/sthrough air that has a tem-perature of 20°C. How far willsound travel in 3 secondsthrough air at 20°C?

distance = speed time

distance = 343 ms 3 s

distance = 1,029 m

Now It’s Your TurnHow far does sound travel in5 seconds through air, water,and steel at 20°C? Use thespeeds given in the chart onthe previous page.

MATH BREAK

High frequency high pitch

Low frequency low pitch



Kidney stones—deposits of calciumsalts that form inside kidneys—cancause a great deal of pain. Sometimesthey are so large that they have to beremoved by a doctor. Surgery wasonce the primary way to remove kid-ney stones, but now ultrasonic wavescan be used to break kidney stonesinto smaller pieces that can pass outof the body with urine.

Frequency and Hearing Some people use dog whistles tocall their dog. But when you see someone blow a dog whis-tle, the whistle seems silent to you. That’s because the fre-quency of the sound wave is out of the range of human hearing.But the dog hears a very high pitch from the whistle andcomes running! The graph below compares the range of fre-quencies that humans and animals can hear.

Frequencies You Can Hear The average human ear can detectsounds that have frequencies between 20 Hz and 20,000 Hz.Examples of sounds within this range include the lowest sounda pipe organ can make (about 40 Hz) and the screech of a bat(10,000 Hz or higher). The range of hearing varies from per-son to person. Young children can often hear sounds with fre-quencies above this range, while many elderly people havedifficulty hearing sounds higher than 8,000 Hz.

Frequencies You Can’t Hear Sounds that are outside therange of human hearing have special names. Sounds with fre-quencies that are lower than 20 Hz are described as infrasonic.Sounds with frequencies that are higher than 20,000 Hz aredescribed as ultrasonic. The sounds are given these namesbecause sonic refers to sound, infra means “below,” and ultrameans “beyond.”

Ultrasonic waves have a variety of applications. For exam-ple, ultrasonic waves are used to clean jewelry and to removeice from metal. Scientists hope to use this technology to removeice from airplane wings, car windshields, and freezers. You willlearn about other uses of ultrasonic waves in the next section.


Frequencies Heard by Different Animals

1

5

2

50

20

500

200

5,000

2,000

50,000

20,000

200,000

10

100

1,000

10,000

100,000

Freq

uenc

y (H

z)

Animal

DogBird

BaleenwhaleCat

Human

Bottlenosedolphin

Bat


The Doppler Effect Have you ever been passed by a car with its horn honking? If so, you probably noticed the sud-den change in pitch—sort of an EEEEEOOoooowwn sound—as the car sped past you. The pitch you heard was higher whilethe car was approaching than it was after the car passed. This is a result of the Doppler effect. For sound waves, theDoppler effect is the apparent change in the frequency of asound caused by the motion of either the listener or the sourceof the sound. Figure 7 explains the Doppler effect. Keep inmind that the frequency of the car horn does not really change;it only sounds like it does. The driver of the car always hearsthe same pitch because the driver is moving with the car.

Loudness Is Related to AmplitudeIf you gently tap a bass drum, you will hear a soft rumbling.But if you strike the drum with a large force, you will hear aloud BOOM! By changing the force you use to strike the drum,you change the loudness of the sound that is created. Loudnessis how loud or soft a sound is perceived to be.

Energy and Vibration The harder you strike a drum, thelouder the boom. As you strike the drum harder, you transfermore energy to the drum. The drum moves with a larger vibra-tion and transfers more energy to the surrounding air. Thisincrease in energy causes air particles to vibrate farther fromtheir rest positions.

Chapter 21542

The sounds made by boom-ing sands are sometimes soloud that scientists workingon the dunes have to shoutto hear each other.

Figure 7 The Doppler effectoccurs when the source of asound is moving relative tothe listener.

The car moves toward the sound waves infront of it, causing the waves to be closertogether and to have a higher frequency.

The car moves away from the sound wavesbehind it, causing the waves to be fartherapart and to have a lower frequency.

A listener in front of the car hears ahigher pitch than a listener behind the car.

a b

c


Increasing Amplitude When you strike adrum harder, you are increasing the ampli-tude of the sound waves being created. Theamplitude of a wave is the maximum distancethe particles in a wave vibrate from their restpositions. The larger the amplitude, the louderthe sound, and the smaller the amplitude,the softer the sound. Figure 8 shows one wayto increase the loudness of a sound. Do theQuickLab on this page to investigate the loud-ness and pitch of sounds.

Measuring Loudness The most common unitused to express loudness is the decibel (dB). Thefaintest sounds an average human ear can hear are ata level of 0 dB. The level of 120 dB is sometimes calledthe threshold of pain because sounds at that level andhigher can cause your ears to hurt. Continued exposure tosounds above 85 dB causes gradual hearing loss by perma-nently damaging the hair cells in your inner ear. The chartbelow shows the decibel levels of some common sounds.


Sound

The softest sounds you can hear

Whisper

Purring cat

Normal conversation

Lawn mower, vacuum cleaner, truck traffic

Chain saw, snowmobile

Sandblaster, loud rock concert,automobile horn

Threshold of pain

Jet engine 30 m away

Rocket engine 50 m away

Decibel level

0

20

25

60

80

100

115

120

140

200

Some Common Decibel Levels

Figure 8 An amplifier increasesthe amplitude of the sound gen-erated by an electric guitar.

Sounding Board

1. With one hand, holda metric ruler onyour desk so thatone end of it hangs over the edge.

2. With your other hand, pullthe free end of the rulerup a few centimeters andlet go.

3. Try pulling the ruler up dif-ferent distances. How doesthe distance affect thesounds you hear? Whatproperty of the soundwave are you changing?

4. Try changing the length ofthe part that hangs overthe edge. What property ofthe sound wave is affected?

5. Record your answers andobservations in yourScienceLog.


“Seeing” Sounds Because sound waves are invisible, theiramplitude and frequency is impossible to measure directly.However, technology can provide a way to “see” sound waves.A device called an oscilloscope (uh SIL uh SKOHP), shown inFigure 9, is used to graph representations of sound waves.

A microphone first converts the sound wave into an elec-tric current. The oscilloscope then converts the electric cur-rent into graphs such as the ones shown in Figure 10. Noticethat the graphs look like transverse waves instead of longitu-dinal waves. The highest points (crests) of these waves repre-sent compressions, and the lowest points (troughs) representrarefactions. By looking at the displays on the oscilloscope,you can quickly see the difference in both amplitude and fre-quency of sound waves.

Figure 9 An oscilloscope can be used to represent sounds.

Figure 10 “Seeing” Sounds

1. In general, how does changing the temperature of amedium affect the speed of sound through that medium?

2. What properties of waves affect the pitch and loudnessof sound?

3. Inferring Conclusions Will a listener notice the Dopplereffect if he or she and the source of the sound are trav-eling toward each other? Explain your answer.

Chapter 21544

REVIEW

The graph on the right has alarger amplitude than the graphon the left. Therefore, the soundrepresented on the right is louderthan the one on the left.

The graph on the right has alower frequency than the one onthe left. So the sound representedon the right has a lower pitchthan the one on the left.

TOPIC: Properties of SoundGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP515


Section

3

reflection sonic boomecho standing waveecholocation resonanceinterference diffraction

Explain how echoes are pro-duced, and describe their use inlocating objects.

Give examples of constructiveand destructive interference ofsound waves.

Identify three sound-wave interac-tions, and give examples of each.


Interactions of Sound WavesBeluga whales, such as those shown in Figure 11, communi-cate by using a wide variety of sounds, including clicks, chirps,whistles, trills, screeches, and moos. The sounds they makecan be heard above and below water. Because of the wide rangeof sounds they make, belugas have been nicknamed “seacanaries.” But belugas use sound for more than just commu-nication—they also use reflected sound waves to find fish,crabs, and shrimp to eat. In this section you’ll learn aboutreflection and other interactions of sound waves.

Reflection of Sound WavesReflection is the bouncing back of a wave after it strikes a bar-rier. You’re probably already familiar with a reflected soundwave, otherwise known as an echo. The amount a sound wavewill reflect depends on the reflecting surface. Sound wavesreflect best off smooth, hard surfaces. That’s why a shout inan empty gymnasium can produce an echo, but a shout in anempty auditorium usually does not, as shown in Figure 12.

Figure 12Sound Reflection and Absorption

Figure 11 Beluga whales dependon sound interactions for survival.

Sound waves easily reflect off the smooth, hardwalls of a gymnasium. That’s why you hear an echo.

In well-designed auditoriums, echoes are reducedby soft materials that absorb sound waves and byirregular shapes that scatter sound waves.


Echolocation Beluga whales use echoes to find food. Theprocess of using reflected sound waves to find objects is calledecholocation. Other animals—such as dolphins, bats, and somespecies of birds—also use echolocation to hunt food and detectobjects in their paths. Figure 13 shows how echolocation works.

Echolocation Technology Humans useechoes to locate objects underwater andunderground by using sonar (sound naviga-tion and ranging). Sonar is a type of elec-tronic echolocation. Figure 14 shows howsonar works. Ultrasonic waves are usedbecause their short wavelengths providemore details about the objects they reflectoff. Sonar can also help navigators on shipsdetect icebergs and can help oceanographersmap the ocean floor.

Figure 13 Bats use echolocationto navigate around barriers andto find insects to eat.

Chapter 21546

Bats emit ultrasonicwaves as they fly.

When the sound waves strike an object, thewaves are reflected back to the bat. The time ittakes for the echoes to reach the bat lets thebat know how far away the obstacle is.

The bat can detect aninsect flying toward itbecause of the Dopplereffect. The echo will have ahigher frequency than thatof the original sound wave.

Figure 14 A depth finder sends ultrasonicwaves down into the water. The time it takesfor the echo to return helps the fishermendetermine the location of the fish.

a

b

c


Insightful Technology

Many people who are blinduse a cane to help themdetect obstacles while they arewalking. Now engineers havedeveloped a sonar cane,shown at right, to help blindpeople even more. The caneemits and detects soundwaves. Based on your knowl-edge of echolocation, explainhow you think this cane works.

Ultrasonography Another type of elec-tronic echolocation is used in a medicalprocedure called ultrasonography. Ultra-sonography uses echoes to “see” inside apatient’s body without performing sur-gery. A device called a transducer producesultrasonic waves, which reflect off thepatient’s internal organs. These echoes arethen converted into images that can beseen on a television monitor, as shown inFigure 15. Ultrasonography is used toexamine kidneys, gallbladders, and otherabdominal organs and to check the devel-opment of an unborn baby in a mother’sbody. Ultrasonic waves are safer than Xrays because sound waves are less harm-ful to human tissue.

1. Describe a place in which you would expect to hear echoes.

2. How do bats use echoes to find insects to eat?

3. Comparing Concepts Explain how sonar and ultra-sonography are similar when used to locate objects.

Figure 15 Images created by ultrasonography arefuzzy, but they are a safe way to see inside apatient’s body.


REVIEW


Interference of Sound WavesAnother interaction of sound waves is interference. Interferenceis the result of two or more waves overlapping. Figure 16 showshow two sound waves can combine by both constructive anddestructive interference.

Orchestras and bands take advantage of constructive inter-ference when several instruments play the same notes. Thesound waves from the instruments combine by constructiveinterference to produce a louder sound. But destructive inter-ference may keep you from hearing the concert. “Dead spots”are areas in an auditorium where sound waves reflecting offthe walls interfere destructively with the sound waves fromthe stage. If you are at a concert and you can’t hear the orches-tra very well, try changing seats before you decide to get yourears checked!

The Sound Barrier As the source of asound—such as a jet plane—acceleratesto the speed of sound, the sound wavesin front of the jet plane compress closerand closer together. Figure 17 showswhat happens as a jet plane reaches thespeed of sound.

Figure 16 Sound waves fromtwo speakers producing soundof the same frequency combineby both constructive anddestructive interference.

Chapter 21548

Figure 17 When a jet plane reaches the speed ofsound, the sound waves in front of the jet combine byconstructive interference. The result is a high-densitycompression that is called the sound barrier.

Constructive InterferenceAs the compressions of one waveoverlap the compressions of anotherwave, the sound will be louderbecause the amplitude is increased.

Destructive InterferenceAs the compressions of one waveoverlap the rarefactions of anotherwave, the sound will be softer because the amplitude is decreased.

Constructiveinterference


Shock Waves and Sonic Booms For the jet in Figure 17 totravel faster than the speed of sound, it must overcome thepressure of the compressed sound waves. Figure 18 shows whathappens as soon as the jet achieves supersonic speeds—speedsfaster than the speed of sound. At these speeds, the soundwaves trail off behind the jet and combine at their outer edgesto form a shock wave.

A sonic boom is the explosive sound heard when a shockwave reaches your ears. Sonic booms can be so loud that theycan hurt your ears and break windows. They can even makethe ground shake as it does during an earthquake.

Standing Waves When you play a guitar, you can makesome pleasing sounds and maybe even play a tune. But haveyou ever watched a guitar string after you’ve plucked it? Youmay have noticed that the string vibrates as a standing wave.A standing wave is a result of interference in which portionsof the wave are at the rest position and other portions havea large amplitude.

Figure 18 When a jet travels at supersonicspeeds, the sound waves it creates spreadout behind it in a cone shape.

You hear a sonic boom when the shock wave reachesyou, not when the jet breaks the sound barrier.


The cracking sound madeby a whip is actually aminiature sonic boomcaused by the shock waveformed as the tip of thewhip travels faster than thespeed of sound!

Self-CheckExplain why two people will not hear a sonic boomat the same time if they are standing a block or twoapart. (See page 724 to check your answer.)

On the edge of the cone, thesound waves combine by con-structive interference to producea shock wave.


Resonant Frequencies Although you can see only one stand-ing wave, the guitar string actually creates several standingwaves of different frequencies at the same time. The frequen-cies at which standing waves are made are called resonantfrequencies. Resonant frequencies are sometimes called by spe-cial names, as shown in Figure 19.

Resonance Would you believe that you can make a guitarstring make a sound without touching it? You can do this ifyou have a tuning fork, shown in Figure 20, that vibrates atone of the resonant frequencies of the guitar string. Strikethe tuning fork, and hold it close to the string. The stringwill start to vibrate and produce a sound. The effect is the

greatest when the resonant frequency ofthe tuning fork matches the fundamen-tal frequency of the string.

Using the vibrations of the tuningfork to make the string vibrate is anexample of resonance. Resonance occurswhen an object vibrating at or near aresonant frequency of a second objectcauses the second object to vibrate.

Higher resonant frequencies arecalled overtones. The first over-tone is twice the frequency ofthe fundamental.

The second overtone is threetimes the fundamental.

The third overtone is four timesthe fundamental.

The lowest resonant frequencyis called the fundamental.

Figure 19 A plucked string vibrates at severalresonant frequencies.

Figure 20 When struck, atuning fork can make cer-tain objects vibrate.

Chapter 21550

A tuning fork and a plastic tubemake beautiful music togetheron page 713 of the LabBook.


Diffraction of Sound WavesHave you ever noticed the different sounds of thunder? Froma distance, thunder sounds like a low rumbling. From nearby,thunder sounds like a loud CRACK! A type of wave interactioncalled diffraction causes this difference. Diffraction is the bend-ing of waves around barriers or through openings. It is howsound waves travel around the corners of buildings and throughdoorways. The amount of diffraction is greatest when the sizeof the barrier or the opening is the same size or smaller thanthe wavelength of the sound waves, as shown in Figure 21.

So what about thunder? Thunder consists of both high-and low-frequency sound waves. When lightning strikes nearby,you hear all the sound waves together as a loud cracking noise.But when the lightning strikes far away, buildings, trees, hills,and other barriers stop most of the high-frequency waves.Only the low-frequency waves can diffract around these largeobjects, and thus you hear only a low rumbling.

1. How is a sound barrier formed?

2. When you are in a classroom, why can you hear voicesfrom the hallway even when you cannot see who istalking?

3. Inferring Conclusions Your friend is playing a song on apiano. Whenever your friend hits a certain key, the lampon top of the piano rattles. Explain why this happens.

Figure 21 Determining the Amount of Diffraction


REVIEW

High-frequency sound waves have short wave-lengths and do not diffract very much when theytravel through a doorway. Therefore, high pitchescan be hard to hear when you are in the next room.

Low-frequency sound waves have longer wave-lengths, so they diffract more through doorways.Therefore, you can hear lower pitches better whenyou are in the next room.

NSTA

TOPIC: Interactions of Sound WavesGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP520


Section

4

sound qualitynoise

Define sound quality. Describe how each family of

musical instruments producessound.

Explain how noise is differentfrom music.

Chapter 21552

Sound QualityHave you ever been told that some music you really like isjust a lot of noise? If you have, you know that people some-times disagree about the difference between noise and music.You probably think of noise as sounds you don’t like and thinkof music as sounds that are interesting and pleasant to hear.But there is actually a difference between music and noise,and the difference has to do with sound quality.

What Is Sound Quality?If the same note is played with the same loudness on a pianoand on a violin, could you tell the instruments apart with-out looking? Although the notes played are identical, you

probably could tell them apartbecause the sounds the instru-ments produce are not thesame. The notes sound differ-ent because each instrumentactually produces several dif-ferent pitches: the fundamentaland several overtones. Thesepitches are modeled in Figure22. The result of several pitchesblending together throughinterference is sound quality.Each instrument has a uniquesound quality. Figure 23 showshow the sound quality differswhen two instruments play thesame note.

Figure 23 An oscilloscope shows the difference in soundquality of the same note played on different instruments.

Fundamental

First overtone

Second overtone

Resulting sound

Figure 22 The top three dia-grams represent three differentpitches played at the same time.The bottom diagram shows theresult when the pitches blendthrough interference.

ViolinPiano


Sound Quality of InstrumentsWhen you listen to an orchestra play you can hear many dif-ferent kinds of instruments. The difference in sound qualityamong the instruments comes from the structural differencesof the instruments. All instruments produce sound with vibra-tions. But the part of the instrument that vibrates and howthe vibrations are made vary from instrument to instrument.Even so, all instruments fall within three main families: stringinstruments, wind instruments, and percussion instruments.

String Instruments Violins, guitars, and banjos are exam-ples of string instruments. They produce sound when theirstrings vibrate after being plucked or bowed. Figure 24 showshow two different string instruments produce sounds.

Figure 24 Cellos and electricguitars are members of thestring family.

553

Self-CheckWhich wave interactionis most important indetermining soundquality? (See page 724to check your answer.)

Cellos and guitars have strings of different thick-nesses. The thicker the string, the lower the pitch.

The pitch of the string can be changed bypushing the string against the neck of theinstrument to change the string’s length.Shorter strings vibrate at higher frequencies.

A string vibrates when abow is pulled across it orwhen the string is plucked.

The vibrations in the cellostring make the bridge vibrate,which in turn makes the bodyof the cello vibrate.

An amplifier con-verts the electricalsignal back into asound wave andincreases the loud-ness of the sound.

g

Pickups on the guitarconvert the vibrationof the guitar string intoan electrical signal.

f

The body of the cello andthe air inside it resonatewith the string’s vibration,creating a louder sound.

e

a

b

c

d


Wind Instruments A wind instrument produces sound whena vibration is created at one end of its air column. The vibra-tion creates standing waves in the air column. Wind instru-ments are sometimes divided into two groups—woodwindsand brass. Examples of woodwinds are saxophones, oboes, andrecorders. Brass instruments include French horns, trombones,and tubas. A woodwind instrument and a brass instrument areshown in Figure 25.

Percussion Instruments Drums, bells, and cymbals areexamples of percussion instruments. They produce sound whenstruck. Different-sized instruments are used to get differentpitches. Usually, the larger the instrument, the lower the pitch. Figure 26 shows examples of percussion instruments.

Figure 25 Clarinets are wood-wind instruments, and trumpetsare brass instruments.

Figure 26 Drums and cymbals in a trap set are examples of percussion instruments.

Chapter 21554

The reed vibrates back and forth whena musician blows into a clarinet.

A trumpet player’s lips vibrate whenthe player blows into a trumpet.

Standing waves are formed in the air columnsof the instruments. The pitch of the instrumentdepends in part on the length of the air col-umn. The longer the column, the lower thepitch.

The length of the air column ina clarinet is changed by closingor opening the finger holes.

The length of the air columnin a trumpet is changed bypushing the valves.

d e

Cymbals vibrate whenstruck together or whenstruck with drumsticks.

The skins of the drums vibratewhen struck with drumsticks.

Each drum in the setis a different size. Thelarger the drum, thelower the pitch.

a b

c


Music or Noise?Most of the sounds we hear are noises. The sound of a truckroaring down the highway, the slamming of a door, and thejingle of keys falling to the floor are all noises. Noise can bedescribed as any undesired sound, especially a nonmusical sound,that includes a random mix of pitches. Figure 27 shows the dif-ference between a musical sound and noise on an oscilloscope.

Noise Pollution The amount of noise around you canbecome so great that it is not only bothersome but can causehealth problems. When noise reaches a level that causes painor damages the body, it is considered noise pollution.

Noise pollution can damage the inner ear, causing perma-nent hearing loss. Noise pollution can also contribute to sleep-lessness, high blood pressure, and stress. Because of these healthconcerns, the federal government has set noise exposure lim-its for people who work in areas with loud noises. Noise pol-lution also makes the environment less livable for humans aswell as wildlife.

1. What is the role of interference in determining sound quality?

2. Name the three families of musical instruments, anddescribe how vibrations are created in each family.

3. Interpreting Graphics Look atthe oscilloscope screen at right.Do you think the sound rep-resented by the wave on thescreen was noise or music?Explain your answer.

Figure 27 A note from a French horn produces a sound wave witha repeating pattern, but noise from a clap produces complex soundwaves with no pattern.


REVIEW

French horn A sharp clap

The Los Angeles International Airportwas built next to the main habitat ofan endangered butterfly speciescalled the El Segundo blue. The noisepollution from the airport has drivenpeople and other animals from thearea, but the butterflies are notaffected because they have no ears!


NSTA

TOPIC: Sound QualityGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP525


Chapter Highlights

Chapter 21556

SECTION 1 SECTION 2

Vocabularywave (p. 535)

medium (p. 536)

outer ear (p. 537)

middle ear (p. 537)

inner ear (p. 537)

Section Notes

• All sounds are created byvibrations and travel aslongitudinal waves.

• Sound waves require a medi-um through which to travel.

• Sound waves travel in alldirections away from theirsource.

• The sounds you hear areconverted into electricalimpulses by your ears andthen sent to your brain forinterpretation.

• Exposure to loud sounds cancause hearing loss andtinnitus.

Vocabularypitch (p. 540)

infrasonic (p. 541)

ultrasonic (p. 541)

Doppler effect (p. 542)

loudness (p. 542)

decibel (p. 543)

Section Notes

• The speed of sound dependson the medium throughwhich the sound is traveling.Changes in temperature ofthe medium can affect thespeed of sound.

• The pitch of a sounddepends on frequency. High-frequency sounds are high-pitched, and low-frequency sounds are low-pitched.

• Humans can hear soundswith frequencies between 20 Hz and 20,000 Hz.

• The Doppler effect is theapparent change in frequencyof a sound caused by themotion of either the listeneror the source of the sound.

• The loudness of a soundincreases as the amplitudeincreases. Loudness isexpressed in decibels.

• An oscilloscope can be usedto “see” sounds.

LabsEasy Listening (p. 710)

Skills CheckMath ConceptsTHE SPEED OF SOUND The speed of sounddepends on the medium through which thesound waves are traveling. The speed of soundthrough wood at 20°C is 3,850 m/s. The dis-tance sound will travel through wood in 5 sec-onds can be calculated as follows:

distance = speed time

= 3,850 ms 5 s

= 19,250 m

Visual UnderstandingHOW THE HUMAN EAR WORKS The human earhas several parts that are divided into three

regions—the outer ear, the middleear, and the inner ear. Study

the diagram on page 537 toreview how the

ear works.


557The Nature of Sound

SECTION 3


echo (p. 545)

echolocation (p. 546)


sonic boom (p. 549)

standing wave (p. 549)

resonance (p. 550)


Section Notes

• Echoes are reflected soundwaves.

• Some animals use echoloca-tion to find food or navigatearound objects. Sonar andultrasonography are types ofecholocation.

• Sound barriers and shockwaves are created by interfer-ence. You hear a sonic boomwhen a shock wave reachesyour ears.

• Standing waves form at an object’s resonant frequencies.

• Resonance occurs when avibrating object causes a sec-ond object to vibrate at oneof its resonant frequencies.

• The bending of sound wavesaround barriers or throughopenings is called diffraction.The amount of diffractiondepends on the wavelengthof the waves as well as thesize of the opening.

LabsThe Speed of Sound (p. 712)

Tuneful Tube (p. 713)

The Energy of Sound (p. 714)

Vocabularysound quality (p. 552)

noise (p. 555)

Section Notes

• Different instruments havedifferent sound qualities.

• The three families of instru-ments are strings, winds, andpercussion.

• The sound quality of noise isnot pleasing because it is arandom mix of frequencies.

SECTION 4


TOPIC: What Is Sound? sciLINKS NUMBER: HSTP505

TOPIC: The Ear sciLINKS NUMBER: HSTP510

TOPIC: Properties of Sound sciLINKS NUMBER: HSTP515

TOPIC: Interactions of Sound Waves sciLINKS NUMBER: HSTP520

TOPIC: Sound Quality sciLINKS NUMBER: HSTP525



KEYWORD: HSTSND




1. Humans cannot hear ? waves becausetheir frequencies are above the range ofhuman hearing. (infrasonic or ultrasonic)

2. In the ? , vibrations are converted toelectrical signals for the brain to interpret.(middle ear or inner ear)

3. The ? of a sound wave depends on itsamplitude. (loudness or pitch)

4. Reflected sound waves are called ? .(echoes or noise)

5. Two different instruments playing thesame note sound different because of ? . (echolocation or sound quality)


Multiple Choice

6. If a fire engine is traveling toward you,the Doppler effect will cause the siren tosounda. higher. c. louder.b. lower. d. softer.

7. The wave interaction most important forecholocation isa. reflection. c. diffraction.b. interference. d. resonance.

8. If two sound waves interfere construc-tively, you will heara. a high-pitched sound.b. a softer sound.c. a louder sound.d. no change in sound.

9. You will hear a sonic boom whena. an object breaks the sound barrier.b. an object travels at supersonic speeds.c. a shock wave reaches your ears.d. the speed of sound is 290 m/s.

10. Instruments that produce sound whenstruck belong to which family?a. strings c. percussionb. winds d. none of the above

11. Resonance can occur when an objectvibrates at another object’sa. resonant frequency.b. fundamental frequency.c. second overtone frequency.d. All of the above

12. The amount of diffraction that a soundwave undergoes depends ona. the frequency of the wave.b. the amplitude of the wave.c. the size of the barrier.d. Both (a) and (c)

13. A technological device that can be used to“see” sound waves is a(n)a. oscilloscope. c. transducer.b. sonar. d. amplifier.

Short Answer

14. Describe how the Doppler effect helps abeluga whale determine whether a fish ismoving away from it or toward it.

15. How is interference involved in forming ashock wave?

16. Briefly describe how the three parts of theear work.


Concept Mapping

17. Use the followingterms to create a concept map: sound,sound wave, pitch,loudness, decibel,hertz, frequency,amplitude.


18. An anechoic chamber is a room wherethere is almost no reflection of soundwaves. Anechoic chambers are often usedto test sound equipment, such as stereos.The walls of such chambers are usuallycovered with foam triangles. Explain whythis design eliminates echoes in the room.

19. Suppose you are sitting in the passengerseat of a parked car. You hear soundscoming from the stereo of another carparked on the opposite side of the street.You can easily hear the low-pitched basssounds but cannot hear any high-pitchedsounds coming from the parked car.Explain why you think this happens.

20. After working in a factory for a month, aman you know complains about a ringingin his ears. What might be wrong withhim? What do you think may havecaused his problem? What can you sug-gest to prevent further hearing loss?

MATH IN SCIENCE

21. How far does sound travel in 4 secondsthrough water at 20°C and glass at 20°C?Refer to the chart on page 35 for thespeed of sound in different media.


Use the oscilloscope screens below to answerthe following questions:

22. Which sound is probably noise?

23. Which represents the softest sound?

24. Which represents the sound with the lowest pitch?

25. Which two sounds were produced by thesame instrument?


a b

c d



ReadingCheck-up


560

Jurassic Bark

Imagine you suddenly hear an incredibly loudhonking sound, like a trombone or a tuba.“Must be band tryouts,” you think. You turn

to find the noise and find yourself face to facewith a 10 m long, 2,800 kg dinosaur with ahuge tubular crest extending back more than 2 m from its snout. Do you run? No—your musi-cal friend, Parasaurolophus, is a vegetarian.

Now there’s no way you’ll bump into thisextinct hadrosaur, a duck-billed dinosaur thatexisted about 75 million years ago in the lateCretaceous period. But through recent advancesin computer technology, you can hear howParasaurolophus might have sounded.

A Snorkel or a Trombone?Parasaurolophus’s crest contained a network oftubes connected to the animal’s breathing pas-sages. Some scientists believe the dinosaursused the distinctive crest to make sounds.Other scientists theorize that the crest allowedParasaurolophus to stay underwater and feed,that it was used to regulate body temperature,or that it allowed the animals to communicatewith each other by exhaling strongly throughthe crest.

The study of the Parasaurolophus’s potentialsound-making ability really began after a 1995expedition in northwestern New Mexico uncov-ered an almost-complete fossil skull of anadult. With this nearly complete skull and somemodern technology, scientists tested the noise-making qualities of the crest.

Dino ScanIn Albuquerque, New Mexico, Dr. Carl Diegert of Sandia National Laboratories and Dr. TomWilliamson of the New Mexico Museum ofNatural History and Science teamed up to useCT (Computed Tomography). With this scanningsystem, they created three-dimensional imagesof the crest’s internal structure. The results

showed that the crest had more tubes than pre-viously thought as well as additional chambers.

Sound That Funky HornOnce the crest’s internal structure was deter-mined, Diegert used powerful computers andspecial software to produce a sound thatParasaurolophus might have made. Since it isnot known whether Parasaurolophus had vocalcords, Diegert made different versions of thesound by simulating the movement of airthrough the crest in several ways. Intrigued byDiegert’s results, other researchers are trying toreproduce the sounds of other dinosaurs. Intime, Parasaurolophus might be just one of aband of musical dinosaurs.

On Your Own Parasaurolophus is just one type ofhadrosaur recognized for the peculiar bonycrest on top of its head. On your own, researchother hadrosaurs that had a bony crest similarto that of the Parasaurolophus. What are thenames of these dinosaurs?

Aside from a role in the Jurassic Park movies, the Parasaurolophusdinosaur’s biggest claim to fame is the enormous crest that extends back from its snout.


561

“Ear”by Jane Yolen

“Jily put on her Ear and sighed. The worldwent from awful silence to the poundingrhythms she loved. Without the Ear she

was locked into her own thoughts and the fewcolors her eyes could pick out. But with the Earshe felt truly connected to the world.”

Jily and her friends, Sanya and Feeny, live in a time not too far in the future. It is a timewhen everyone’s hearing is damaged. Peoplecommunicate using sign language—unless theyput on their Ear. Then the whole world is filledwith sounds. Of course, there are rules. No Earsallowed in school. Ears are only to be worn onthe street, at night. Life is so much richer withan Ear, a person would have to be crazy to go without one.

The Low Down, the first club Jily and herfriends visit, is too quiet for Jily’s tastes. Shewants to leave and tries to find Sanya andFeeny. But Sanya is dancing by herself, eventhough there is no music. When Jily finds Feeny,they notice some Earless kids their own age.Earless people never go to clubs, and Jily findstheir presence offensive. But Feeny is intrigued.

Everyone is given an Ear at the age of 12but has to give it up at the age of 30. Whywould these kids want to go out without theirEars before the age of 30? Jily thinks the idea isridiculous and doesn’t stick around to find outthe answer to such a question. But, it is ananswer that will change her life by the end ofthe next day.

Read the rest of Jily’s story, “Ear” by JaneYolen, in the Holt Anthology of Science Fiction.


562 Chapter 22

What Is Light? . . . . . . 564MathBreak . . . . . . . . . 566Internet Connect . . . . 566

The ElectromagneticSpectrum . . . . . . . . . . 567Astronomy Connection . . . . . . . . 567

Biology Connection . . . 572Apply . . . . . . . . . . . . . 573Internet Connect . . . . 574

Interactions ofLight Waves . . . . . . . . 575QuickLab. . . . . . . . . . . 577Internet Connect . . . . 580

Light and Color . . . . . 581QuickLab. . . . . . . . . . . 584Geology Connection . . 585Internet Connect . . . . 585

Chapter Review . . . . . . . . . 588


LabBook . . . . . . . . . . . 716–719

The Nature of LightThe Nature of Light

What on Earth . . .?What kind of alien life lives on this planet? Actually, thisisn’t a planet at all. It’s a photograph of something much,much smaller. Have you guessed yet? It’s an ordinary soapbubble! The brightly colored swirls on the surface of thisbubble are reflections of light. In this chapter, you willlearn more about light, including how waves interact andwhy you can see different colors like the ones on the sur-face of this soap bubble.


1. What is light?2. How do light waves

interact?3. Why are you able to see

different colors?


563

COLORS OF LIGHTIs white light really white? In thisactivity, you will use a spectroscopeto answer that question.

Procedure

1. Your teacher will give you a spectroscope or instructions formaking one.

2. Turn on an incandescent lightbulb. Look at the light bulbthrough your spectroscope. In yourScienceLog, write a description ofwhat you see.

3. Repeat step 2 looking at a fluorescent light. Again, in yourScienceLog, describe what you see.

Analysis

4. Compare what you saw in step 2with what you saw in step 3.

5. Both kinds of bulbs produce white light. What did you learnabout white light using the spectroscope?

6. Light from the sun is white light.Make inferences about what youwould see if you looked at sunlightusing a spectroscope.Caution: Do NOT use your spec-troscope to look at the sun. It doesnot give enough protection againstbright sunlight.

The Nature of LightCopyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 22564

What Is Light?We rely on light from the sun and from electric bulbs to helpus see. But what exactly is light? Scientists are still studyinglight to learn more about its makeup and characteristics.Fortunately, much has already been discovered about light, asyou will soon find out. You may even become enlightened!

Light Is an Electromagnetic WaveLike sound, light is a type of energy that travels as a wave. Butunlike sound, light does not require a medium through whichto travel. Light is an electromagnetic wave (EM wave). An EMwave is a wave that can travel through space or matter andconsists of changing electric and magnetic fields. A field is aregion around an object that can exert a force, a push or pull,on another object without actually touching that object. Forexample, a magnet is surrounded by a magnetic field that canpull a paper clip toward it. But keep in mind that this field,like all fields, is not made of matter.

Figure 1 shows a diagram of an electromagnetic wave. Noticethat the electric and magnetic fields are at right angles—orperpendicular—to each other. These fields are also perpendicularto the direction of the wave motion. Because of this arrange-ment, electromagnetic waves are transverse waves.

Figure 1 Electromagnetic wavesare transverse waves.

Directionof travel

Electric fieldMagnetic field

The electric field is perpendicularto the magnetic field.

Section

1

electromagnetic waveradiation

Explain why electromagneticwaves are transverse waves.

Describe how electromagneticwaves are produced.

Calculate distances traveled bylight using the value for speed of light.


How Light Is ProducedAn EM wave is produced by the vibration of an electricallycharged particle. A particle with an electric charge is surroundedby an electric field. When the particle vibrates, or moves backand forth, the electric field around it vibrates too. When theelectric field starts vibrating, a vibrating magnetic field is cre-ated. The vibration of an electric field and a magnetic fieldtogether produces an EM wave that carries energy released bythe original vibration of the particle. The emission of energyin the form of EM waves is called radiation.

Sounds complicated, right? To better understand how lightis produced, think about the following example. When youturn on a lamp, the electrical energy supplied to the filamentin the bulb causes the atoms in the filament to vibrate. Chargedparticles inside the atoms then vibrate, and light is produced,as shown in Figure 2.

The Nature of Light 565

Figure 2 The Production of Light

The Split Personality of LightThe fact that light is a wave explains certain behaviors of light, but notothers. These puzzling behaviors of light are easier to explain if light isthought to consist of particles instead of waves. Scientists think thatlight has the properties of both a particle and a wave. Albert Einsteinwas one of many scientists who researched the dual nature of light.The idea that light can act as either particles or waves is known asthe particle-wave theory of light.

Electrons (negatively chargedparticles) in an atom move aboutthe nucleus at different distancesdepending on the amount ofenergy they have. When an elec-tron absorbs energy, it can jumpto a new position.

a b

c

This new position is generallyunstable, and the electron maynot stay there very long. Theelectron returns to its originalposition, releasing the energy it absorbed in a tiny “packet”called a photon.

The movement of electronsback and forth creates astream of photons. Thisstream of photons can bethought of as waves ofvibrating electric and mag-netic fields. The stream ofphotons (the EM wave)carries the energy releasedby the electrons.

Extra! Extra! Read all abouthow light-producing firefliessave people’s lives! Turn to

page 590.

NucleusElectron

Photon

Energy levels


The Speed of LightScientists have yet to discover anything in the universe thattravels faster than light. In the near-vacuum of space, thespeed of light is about 300,000,000 m/s. Light travels slightlyslower in air, glass, and other types of matter. (Keep in mindthat even though EM waves do not require a medium, theycan travel through many substances.) Believe it or not, lightcan travel more than 880,000 times faster than sound! Thisexplains the phenomenon described in Figure 3. And if youcould run at the speed of light, you could travel around Earth7.5 times in 1 second.

Chapter 22566

Just How Fast Is Light?To give you an idea of howfast light travels, calculate thetime it takes for light to travelfrom Earth to the moon. Thedistance from Earth to themoon is 382,000,000 m.

speed = distitman

ece

This equation can berearranged to solve for time:

time = dsispteaendce

time =

time = 1.27 seconds

Now It’s Your TurnThe distance from the sun toEarth is 150,000,000,000 m.Calculate the time it takes forlight to travel that distance.

382,000,000 m300,000,000 m/s

MATH BREAK

REVIEW

Figure 3 Although thunder and lightning are produced at thesame time, you usually see lightning before you hear thunder.That’s because light travels much faster than sound.

1. Why are electromagnetic waves transverse waves?

2. How is a sound wave different from an EM wave?

3. How does a charged particle produce an EM wave?

4. Making Inferences Explain why EM waves do not requirea medium through which to travel.

5. Doing Calculations The distance from the sun to Jupiteris 778,000,000,000 m. How long does it take for lightfrom the sun to reach Jupiter?

NSTA

TOPIC: Light EnergyGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP529




Scientists know that all electromagneticwaves in empty space travel at thesame speed. If EM waves traveled atdifferent speeds, planets, stars, andgalaxies would appear to be in differ-ent places depending upon which EMwave was used to view them. Forexample, using X rays to view a starmight make the star appear to be in adifferent place than if radio waveswere used.


The ElectromagneticSpectrumWhen you look around, you can see objects because lightreflects off them. But if a bee looked at the same objects, itwould see them differently, as shown in Figure 4. This is becausebees can see a kind of light that you can’t see. This type oflight is called ultraviolet light.

It might seem strange to you to call something you can’tsee light, because the light you are most familiar with is visiblelight. But ultraviolet light is very similar to visible light. Bothvisible light and ultraviolet light are types of EM waves. Inthis section you will learn about many other types of EMwaves, including X rays, radio waves,and microwaves.

Characteristics of EM WavesEven though there are many types of EM waves, each type ofwave travels at the same speed in a vacuum—300,000,000 m/s.How is this possible? Well, the speed of a wave is determinedby multiplying its wavelength by its frequency. So EM waveshaving different wavelengths can travel at the same speed aslong as their frequencies are also different. The entire rangeof EM waves is called the electromagnetic spectrum. Categoriesof waves in the EM spectrum include radio waves, microwaves,and visible light.

Figure 4 The petals of theflower on the right looksolid yellow to you. But abee may see dark ultra-violet markings that makethe same flower appearquite different to the bee.

Section

2

electromagnetic spectrum

Identify how EM waves differfrom each other.

Describe some uses for radiowaves and microwaves.

Give examples of how infraredwaves and visible light areimportant in your life.

Explain how ultraviolet light,X rays, and gamma rays can beboth helpful and harmful.


A radio station convertssound into an electriccurrent. The current pro-duces radio waves thatare sent out in alldirections by theantenna.

Radio WavesRadio waves cover a wide range of waves in the EM spectrum.Radio waves have some of the longest wavelengths and thelowest frequencies of all EM waves. Therefore, radio waves

are low energy waves. They carry enoughenergy, however, to be used for broad-

casting radio signals. Figure 5 showshow this process works.

Radio stations encode soundinformation into radio waves by varying either the waves’amplitude or their frequency.Changing amplitude or frequencyis called modulation. You proba-bly know that there are AM radiostations and FM radio stations.The abbreviation AM stands foramplitude modulation, and theabbreviation FM stands for fre-quency modulation. AM radiowaves have longer wavelengthsthan FM radio waves.

Chapter 22568

The electromagnetic spectrum is arranged from longto short wavelength or from low to high frequency.

Radio waves Microwaves Infrared

All radio and televisionstations broadcast

radio waves.

Despite their name,microwaves are not

the shortest EM waves.

Infrared means“below red.”

Figure 5 Radio waves cannotbe heard, but they carryenergy that can be convertedinto sound.

Electromagnetic Spectrum

A radio receives radio waves and thenconverts them into an electric current,which is then converted to sound.

2

1



Ultraviolet

Visible light

Visible light contains all the

colors you can see.

X rays Gamma rays

Gamma rays are produced by some nuclear reactions.

X rays were discoveredin the early 1900s.

Ultravioletmeans

“beyond violet.”

nuclear power plantpicture

LGT-P01-010d-P

Figure 6 The difference in the wavelengths of AM and FM radiowaves affects how the waves interact with a layer of the atmos-phere called the ionosphere.

Decreasing wavelength

Increasing frequency

AM radio waves can reflect off theionosphere. This helps AM wavestravel long distances.

FM radio waves pass through theionosphere. Therefore, FM wavescannot travel as far as AM waves.

Ionosphere

AM and FM Radio Waves Although AM radio waves cantravel farther than FM waves, as shown in Figure 6, many sta-tions—especially those that broadcast mostly music—use FMwaves. That’s because more information can be encoded byusing frequency modulation than by using amplitude modu-lation. Because FM waves carry more information, music broad-cast from FM stations sounds better.

Ionosphere


Television and Radio Waves Television signals are also car-ried by radio waves. Most television stations broadcast radiowaves that have shorter wavelengths and higher frequenciesthan those broadcast by radio stations. However, television sig-nals are still broadcast using amplitude modulation and fre-quency modulation. Television stations use frequency-modulatedwaves to carry sound and amplitude-modulated waves to carrypictures.

Some waves carrying television signals are transmitted tosatellites around the Earth. The waves are amplified and relayedback to ground antennae and then travel through cables totelevisions in homes. This is how cable television works.

MicrowavesMicrowaves have shorter wavelengths and higher frequenciesthan radio waves. Therefore, microwaves carry more energythan radio waves. You are probably familiar with microwaves—they are created in a microwave oven, like the model illus-trated in Figure 7.

Chapter 22570

The frequencies at whichradio and television stationsbroadcast in the UnitedStates are assigned by theFederal CommunicationsCommission (FCC). In fact,the FCC has assigned fre-quencies for all devices thatuse radio waves. Suchdevices include garagedoor openers, baby moni-tors, radio controlled toys,and wildlife tracking collars.

Figure 7 How a Microwave Oven Works

The microwaves reflect off ametal fan and are directedinto the cooking chamber.

Microwaves can penetrateseveral centimeters intothe food.

A device called a magnetron producesmicrowaves by accelerating charged particles.

a

b

c d The energy of the microwaves causeswater molecules inside the food tovibrate. The vibration of the watermolecules causes the temperature ofthe food to increase.


Radar Microwaves are also used in radar. Radar(radio detection and ranging) is used to detect thespeed and location of objects. Figure 8 shows apolice officer using radar to determine the speedof a car. The officer points the radar device at acar and presses a button. The device emits shortpulses of microwaves that reflect off the car andreturn to the device. The rate at which the wavesare reflected is used to calculate the speed of thecar. Radar is also used to monitor the movementof airplanes and to help ship captains navigate atnight or in foggy weather.

Infrared WavesInfrared waves have shorter wavelengths and higher frequen-cies than microwaves. So infrared waves can carry more energythan microwaves and radio waves carry.

When you sit outside on a sunny summer day, you feelwarm because of infrared waves emitted by the sun. Infraredwaves are absorbed by your skin when they strike your body.The energy of the waves causes the particles in your skin tovibrate faster, and you feel the increased vibration as anincrease in temperature.

The sun is not the only source of infrared waves. Objectsthat emit infrared waves include stars, planets, buildings, trees,and you! The amount of infrared radiation emitted by anobject varies depending on the object’s temperature. Warmerobjects give off more infrared radiation than cooler objects.

Your eyes can’t see infrared waves, but there are devicesthat can detect infrared radiation. For example, infrared binoc-ulars convert infrared radiation into light you can see. Suchbinoculars can be used to observe animals at night. Figure 9shows how certain photographic films are sensitive to infraredradiation.


REVIEW

Figure 9 In this photograph,brighter colors indicate highertemperatures.

1. How do infrared waves differ from radio waves in termsof frequency and wavelength?

2. Describe two ways that radio waves are used fortransmitting information.

3. Inferring Relationships Why do the frequencies of EMwaves increase as the wavelengths decrease?

Figure 8 Police officers use radar to detectcars going faster than the speed limit.


Visible LightVisible light is the very narrow range of wavelengths and fre-quencies in the electromagnetic spectrum that humans cansee. Humans see the different wavelengths as different colors,as shown in Figure 10. The longest wavelengths are seen as redlight, and the shortest wavelengths are seen as violet light.Because violet light has the shortest wavelength, it carries themost energy of the visible light waves.

Colors of Light The range of colors is called the visible spec-trum. When you list the colors, you might use the imaginaryname “Roy G. Biv” to help you remember their order. The let-ters in Roy’s name represent the first letter of each color ofvisible light: red, orange, yellow, green, blue, indigo, and vio-let. When all the colors of visible light are combined, you seethe light as white light. Sunlight and light from incandescentlight bulbs and fluorescent light bulbs are examples of whitelight. You can see the visible spectrum in Figure 11.

Chapter 22572


Visible light provides the energy nec-essary for photosynthesis—the pro-cess by which plants make their ownfood. Photosynthesis is important toyou for two reasons. First, duringphotosynthesis, plants produce oxy-gen for you to breathe. Second, thefood produced by plants providesyour body with energy. When youeat plants, or eat meat from animalsthat ate plants, you get energy to livefrom the food produced throughphotosynthesis.

Figure 11 The visible spectrumcontains all colors of light.

Figure 10 White light, such as light from the sun, is actuallyvisible light of all wavelengths combined. You see all the colors of visible light in a rainbow.

R O Y G B I V


Ultraviolet LightUltraviolet light is another type of electromagnetic wave pro-duced by the sun. Ultraviolet waves have shorter wavelengthsand higher frequencies than visible light. Therefore, ultravio-let waves carry more energy than visible light carries. This greateramount of energy affects us in both positive and negative ways.

Positive Effects On the positive side, ultraviolet wavesproduced artificially by ultraviolet lamps are used to killbacteria on food and surgical instruments. In addition,limited exposure to ultraviolet light is beneficial to your body. When exposed to ultraviolet light,skin cells produce vitamin D, a substancenecessary for the absorption of calcium bythe intestines. Without calcium, your teethand bones would be very weak.

Negative Effects On the negativeside, overexposure to ultraviolet lightcan cause sunburn, skin cancer, dam-age to the eyes, wrinkles, and prema-ture aging of the skin. Fortunately, muchof the ultraviolet light from the sun doesnot reach the surface of the Earth. But youshould still protect yourself against the ultra-violet light that does reach you. To do so, youshould use sunscreen with a high SPF (SunProtection Factor) and wear sunglasses thatblock out ultraviolet light, like the person onthe left in Figure 12. You need this protectioneven on overcast days because ultraviolet lightcan travel through clouds.

573

Blocking the Sun

Sunscreens contain a chemical thatprevents ultraviolet light from pene-trating your skin. When you look ata bottle of sunscreen, you will seethe abbreviation SPF followed by anumber. The number is a guide tohow long you can stay in the sun

without getting a sunburn. Forexample, if you use a sunscreenwith SPF 15 and you normally burnafter being in the sun for 10 min-utes, you will be able to stay in thesun for 150 minutes without gettingburned. Why do you think peoplewho burn easily need a higher SPF?

The Nature of Light

Figure 12 Sunscreen offers protectionagainst a painful sunburn.


X Rays and Gamma RaysX rays and gamma rays have some of the shortest wavelengthsand highest frequencies of all EM waves. X rays carry a greatdeal of energy and easily penetrate a variety of materials. Thischaracteristic makes X rays useful in the medical field, as shownin Figure 13. However, too much exposure to X rays can dam-age or kill living cells. Patients receiving X-ray examinationsoften wear a lead-lined apron to protect the parts of the bodythat do not need X-ray exposure.

Gamma rays carry large amounts of energy and can pene-trate materials very easily. Every day you are exposed to smallamounts of gamma rays that do not harm you. Because of theirhigh energy, gamma rays are used to treat some forms of can-cer. Radiologists focus the rays on tumors inside the body tokill the cancer cells. While this treatment can have positiveeffects, it often has negative side effects because some healthycells are also killed.

Chapter 22574

Figure 13 If you fall and hurtyour arm, a doctor might use anX-ray machine to check forbroken bones.

X rays travel easily throughskin and muscle but areabsorbed by bones.

The X rays thatare not absorbedstrike the film.

Bright areas appear onthe film where X rays areabsorbed by the bones.

REVIEW

1. Explain why ultraviolet light, X rays, and gamma rayscan be both helpful and harmful.

2. Describe how three different types of electromagneticwaves have been useful to you today.

3. Comparing Concepts Compare the wavelengths and fre-quencies of infrared, ultraviolet, and visible light. Howdoes the energy carried by each type of wave comparewith the others?

NSTA

TOPIC: The Electromagnetic SpectrumGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP530



Interactions of Light WavesHave you ever seen a cat’s eyes glow in the dark when lightshines on them? Cats have a special layer of cells in the backof their eyes that reflects light. This layer helps the cat see bet-ter by giving the eyes another chance to detect the light.Reflection is just one way light waves interact. All types of EMwaves interact in several ways. Because we can see visible light,it is easier to explain interactions involving visible light.

ReflectionReflection occurs when light or any other wave bounces offan object. When you see yourself in a mirror, you are actu-ally seeing light that has been reflected twice—first from youand then from the mirror. Reflection allows you to see objectsthat don’t produce their own light. When light strikes an object,some of the light reflects off of it and is detected by your eyes.

But if light is reflecting off you and off the objects aroundyou, why can’t you see your reflection on a wall? To answerthis question, you must first learn about the law of reflection.

The Law of Reflection Light reflects off surfaces the sameway that a ball bounces off the ground. If you throw the ballstraight down against a smooth surface, it will bounce straightup. If you bounce it at an angle, it will bounce away at anangle. The law of reflection states that the angle of incidenceis equal to the angle of reflection. Incidence is the falling of abeam of light on a surface. Figure 14 illustrates this law.

Figure 14 The Law of Reflection

The beam of light travel-ing toward the mirror iscalled the incident beam.

The beam of lightreflected off the mirror iscalled the reflected beam.

The angle between the incident beam andthe normal is called the angle of incidence.

The angle between the reflected beam andthe normal is called the angle of reflection.

A line perpendicularto the mirror’s surfaceis called the normal.

Section

3

reflection refractionlaw of reflection diffractionabsorption interferencescattering

Compare regular reflection withdiffuse reflection.

Describe absorption andscattering of light.

Explain how refraction can cre-ate optical illusions and separatewhite light into colors.

Describe diffraction and interfer-ence of light.


Types of Reflection So back to the question, “Why can yousee your reflection in a mirror but not in a wall?” The answerhas to do with the differences between the two surfaces. If thereflecting surface is very smooth, like a mirror or polished metal,light beams reflect off all points of the surface at the same angle.This is called regular reflection. If the reflecting surface is slightlyrough, like a wall, light beams will hit the surface and reflectat many different angles. This is called diffuse reflection. Figure 15illustrates the difference between the two types of reflection.

Absorption and ScatteringYou have probably noticed that when you use aflashlight, objects that are closer to you appearbrighter than objects that are farther away. Thelight appears to weaken the farther it travels fromthe flashlight. This happens partially because thebeam spreads out and partially because of absorp-tion and scattering.

Absorption of Light The transfer of energycarried by light waves to particles of matter iscalled absorption. When you shine a flashlightin the air, the air particles absorb some of theenergy from the light. This causes the light tobecome dim, as shown in Figure 16. The fartherthe light travels from the flashlight, the more itis absorbed by air particles.

Chapter 22576

Figure 16 A beam of light becomes dimmerpartially because of absorption and scattering.

Diffuse reflection occurs when light beamsreflect at many different angles. You can’t see areflection because not all of the reflected light isdirected toward your eyes.

Regular reflection occurs when light beams arereflected at the same angle. When your eyedetects the reflected beams, you can see a reflec-tion on the surface.

Figure 15 Regular Reflection Vs. Diffuse Reflection

Scattering of Light The release of light energy by particlesof matter that have absorbed energy is called scattering. Whenthe light is released, it scatters in all directions. Light from aflashlight is scattered out of the beam by air particles. Thisscattered light allows you to see objects outside of the beam,as shown in Figure 16 on the previous page. However, becauselight is scattered out of the beam, the beam becomes dimmer.

Scattering makes the sky blue. Light with shorter wave-lengths is scattered more than light with longer wavelengths.Sunlight is made up of many different colors of light, but bluelight (which has a very short wavelength) is scattered morethan any other color. So when you look at the sky, you see abackground of blue light. You can learn more about the scat-tering of light by doing the QuickLab at right.

RefractionImagine that you and a friend are at a lake. Your friend wadesinto the water. You look at her and are startled to see that herfeet look like they are separated from her legs! You know herfeet did not come off, so how can you explain what you see?The answer has to do with refraction.

Refraction is the bending of a wave as it passes at an anglefrom one medium to another. Refraction of light waves occursbecause the speed of light varies depending on the materialthrough which the waves are traveling. In a vacuum, lighttravels at 300,000,000 m/s, but it travels more slowly throughmatter. When a wave enters a new medium at an angle, thepart of the wave that enters first begins traveling at a differ-ent speed from the rest of the wave. Figure 17 shows how alight beam is bent by refraction.

Figure 17 Light travels moreslowly through glass than itdoes through air. Therefore,light refracts as it passes at anangle from air to glass or fromglass to air.

The Nature of Light 577Copyright © by Holt, Rinehart and Winston. All rights reserved.

If light passes into a medium where the speed oflight is faster, the light bends toward the boundary.

If light passes into a medium where thespeed of light is slower, the light bends awayfrom the boundary between the media.

Light in

Scattering Milk

1. Fill a clear 2 L plastic bottle with water.

2. Turn the lights off, andshine a flashlight throughthe water. Look at thewater from all sides of thebottle. Describe what yousee in your ScienceLog.

3. Add a few drops of milk tothe water, and shake thebottle to mix it up.

4. Repeat step 2. Describeany color changes. If youdon’t see any, add moremilk until you do.

5. How is the water-and-milkmixture like air particles inthe atmosphere? Write youranswer in your ScienceLog.


Optical Illusions Normally whenyou look at an object, the lightreflecting off the object travels in astraight line from the object to youreye. Your brain always interpretslight as traveling in straight lines.However, when you look at anobject that is underwater, the lightreflecting off the object does nottravel in a straight line. Instead, itrefracts. Figure 18 shows how refrac-tion creates an optical illusion.

Refraction and Color Separation You havealready learned that white light is actually com-posed of all the colors of visible light. You alsoknow that the different colors correspond to dif-ferent wavelengths. When white light is re-fracted, the amount that the light bends dependson its wavelength. Light waves with short wave-lengths bend more than light waves with longwavelengths. Because of this, white light can beseparated into different colors during refraction,as shown in Figure 19. Color separation duringrefraction is responsible for the formation of rain-bows. Rainbows are created when sunlight isrefracted by water droplets.

Chapter 22578

Figure 19 A prism is a piece ofglass that separates white light intothe colors of visible light by refraction.

Light passing through aprism is refracted twice—once when it enters andonce when it exits.

Violet light, which has ashort wavelength, is refractedmore than red light, whichhas a long wavelength.

Figure 18 Refraction can create the illusionthat the feet of the person in the water areseparated from her legs. Try this for yourself!


DiffractionRefraction isn’t the only way light waves are bent. Diffractionis the bending of waves around barriers or through openings.The diffraction of light waves is not always easy to see. Thediffraction of water waves, shown in Figure 20, is easier to see.The amount a wave diffracts depends on its wavelength andthe size of the barrier or the opening. The greatest amount ofdiffraction occurs when the barrier or opening is the same sizeor smaller than the wavelength.

The wavelength of light is very small—about 100 timessmaller than the thickness of a human hair! So in order forlight to diffract very much, light has to be passing througha slit or some other opening that is very narrow.

Light waves cannot diffract very much around large obsta-cles, such as buildings. That’s why you can’t see around cor-ners. But light waves always diffract a small amount. You canobserve light waves diffracting if you examine the edges ofa shadow. Diffraction causes the edges of shadows to be blurry.

InterferenceInterference is a wave interaction that occurs when two ormore waves overlap. Overlapping waves can combine by con-structive or destructive interference.

Constructive Interference When waves combine by con-structive interference, the resulting wave has a greater amplitudethan the individual waves had. Constructive interference oflight waves can be observed when light of one wavelengthshines through two small slits onto a screen. The light on thescreen will appear as a series of alternating bright and darkbands. The bright bands result from light waves combiningthrough constructive interference to create a light wave witha greater amplitude.

Figure 20 Water waves areoften used to model the behaviorof light waves.

579The Nature of Light

Two lamps are brighter thanone, but it’s not because ofconstructive interference.It’s because two lamps pro-duce more energy in theform of photons than onelamp. As a result, the lighthas a greater intensity,which makes the roombrighter.


Destructive Interference When waves combine by destruc-tive interference, the resulting wave has a smaller amplitudethan the individual waves had. Therefore, when light wavesinterfere destructively, the result will be dimmer light.

You do not see constructive or destructive interference ofwhite light. To understand why, remember that white light iscomposed of waves with many different wavelengths. Thewaves rarely line up to combine in total destructive interfer-ence. However, if light of only one wavelength is used, bothconstructive and destructive interference are easily observed,as illustrated in Figure 21.

Chapter 22580

Constructiveinterference

Destructiveinterference

REVIEW

Figure 21 Constructive and Destructive Interference

Red light of one wavelength passesbetween two tiny slits.

The light waves diffractas they pass throughthe tiny slits.

If you put a screen in front of the slits, you will see alternatingbright and dark bands.

The diffracted light waves interfereboth constructively and destructively.

1. Explain the difference between absorption and scattering.

2. Why does a straw look bent in a glass of water?

3. Why do the edges of shadows seem blurry? Explain youranswer.

4. Applying Concepts Explain why you can see your reflec-tion on a spoon but not on a piece of cloth.

NSTA

TOPIC: Reflection and RefractionGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP545


Figure 22 Light is transmitted, reflected, andabsorbed when it strikes the glass in a window.


Light and ColorHave you ever wondered whatgives an object its color? Youalready know that whitelight is made of all the col-ors of light. But when yousee fruit in white light, yousee color. For example, straw-berries are red and bananas are yel-low. Why aren’t they all white? And how cana soda bottle be green and let you see through it at thesame time? To answer these questions, you must first learn howlight interacts with matter. Then you will understand why objectshave different colors.

Light and MatterWhen light strikes any form of matter, it can interact with thematter in three different ways—it can be reflected, absorbed,or transmitted. You learned about reflection and absorption inthe previous section. Transmission is the passing of lightthrough matter. You see the transmission of light all the time.All of the light that reaches your eyes is transmitted throughair. Light can interact with matter in several ways at the sametime, as shown in Figure 22.

You can see the glass and your reflection init because light is reflected off the glass.

You can see objects outside because light istransmitted through the glass.

The glass feels warm when you touch itbecause some light is absorbed by the glass.

Section

4

transmission opaquetransparent pigmenttranslucent

Name and describe the threeways light interacts with matter.

Explain how the color of anobject is determined.

Compare the primary colors oflight and the primary pigments.


Types of Matter Matter through which visible light is eas-ily transmitted is said to be transparent. Air, glass, and waterare examples of transparent matter. You can see objects clearlywhen you view them through transparent matter.

Sometimes windows in bathrooms are made of frosted glass.If you try to look through one of these types of windows, youwill see only blurry shapes. You can’t see clearly through afrosted window because it is translucent. Translucent mattertransmits light but also scatters the light as it passes throughthe matter. Wax paper is an example of translucent matter.

Matter that does not transmit any light is said to be opaque.You cannot see through opaque objects. Metal, wood, and thisbook are examples of opaque objects. You can compare trans-parent, translucent, and opaque matter in Figure 23.

Colors of ObjectsHow does the interaction of light with matter determine anobject’s color? You already know that the color of light is deter-mined by the wavelength of the light wave. Red has the longestwavelength, violet has the shortest wavelength, and other col-ors have wavelengths in between.

The color that an object appears to be is determined bythe wavelengths of light that reach your eyes. Light reachesyour eyes after being reflected off an object or after being trans-mitted through an object. After reaching your eyes, light isconverted into electrical impulses and interpreted by your brainas colors.

Figure 23 What’s for Lunch?

What’s a bean’s favorite color?It’s not a riddle, it’s an

experiment on page 716 of the LabBook.

Chapter 22582

Transparent plastic makes it easy to see what you are having for lunch.

Opaque aluminum foil makes it impossible to see your lunchwithout unwrapping it.

Translucent wax paper makes it a littleharder to see exactly what’s for lunch.

Colors of Opaque Objects When white light strikes a col-ored opaque object, some colors of light are absorbed andsome are reflected. Only the light that is reflected reaches youreyes and is detected. Therefore, the colors of light that arereflected by an opaque object determine the color you see. Forexample, if your sweater reflects blue light and absorbs allother colors, you will see that the sweater is blue. Anotherexample is shown in Figure 24.

If green objects reflect green light and red objectsreflect red light, what colors of light are reflected bythe cow shown at right? Remember that white lightincludes all colors of light. So white objects—such asthe white hair in the cow’s hide—appear whitebecause all the colors of light are reflected. On theother hand, black is the absence of color. When lightstrikes a black object, all the colors are absorbed.

Colors of Transparent and Translucent ObjectsThe color of transparent and translucent objects isdetermined differently from the color of opaqueobjects. Ordinary window glass is colorlessin white light because it transmits all thecolors that strike it. However, some trans-parent objects are colored. When youlook through colored transparent ortranslucent objects, you see the colorof light that was transmittedthrough the material. All the othercolors were absorbed, as shownin Figure 25.

583

Figure 24 When white lightshines on a strawberry, only redlight is reflected. All other colorsof light are absorbed. Therefore,the strawberry looks red to you.

Self-CheckIf blue light shines on a white sheet of paper,what color does thepaper appear to be?

(Turn to page 724 tocheck your answer.)

The Nature of Light

Figure 25 This bottle isgreen because the plastictransmits only green light.



Mixing Colors of Light In order to get white light, you need to combine all colors oflight, right? Well, that’s one way of doing it. You can also getwhite light by adding just three colors of light together—red,blue, and green—as shown in Figure 26. In fact, these threecolors can be combined in different ratios to produce all col-ors of visible light. Red, blue, and green are therefore calledthe primary colors of light.

Color Addition When colors of light combine, more wave-lengths of light are present. Therefore, combining colors oflight is called color addition. When two primary colors areadded together, a secondary color is produced. The secondarycolors are cyan (blue plus green), magenta (blue plus red), andyellow (red plus green).

Mixing Colors of PigmentIf you have ever tried mixing paints in art class, you knowthat you can’t make white paint by mixing red, blue, andgreen paint. The difference between mixing paint and mixinglight is due to the fact that paint contains pigments. A pigmentis a material that gives a substance its color by absorbing somecolors of light and reflecting others.

Chapter 22584

The colors you see on acolor television are pro-duced by color addition ofthe primary colors of light.A television screen is madeup of groups of tiny red,green, and blue dots. Thesedots are made of chemicalscalled phosphors. Eachphosphor dot will glow red,green, or blue—dependingon the type of phosphor itis—when the dot is hit by anelectron beam. The colorsemitted by the glowingphosphor dots add togetherto produce all the differentcolors you see on the screen.

Figure 26 Primary colors—written in white—combine to producewhite light. Secondary colors—written in black—are the result oftwo primary colors added together.

Blue

Cyan

Magenta Yellow

Red

Green

Rose-Colored Glasses?

1. Obtain four plastic filters—red, blue, yellow, andgreen.

2. Look through one filter atan object across the room.Describe the object’s color.

3. Repeat step 2 with each ofthe filters.

4. Repeat step 2 with two orthree filters together.

5. Why do you think the col-ors change when you usemore than one filter?

6. Write your observationsand answers in yourScienceLog.

Almost everything contains pigments. In fact, pigments giveobjects color. Chlorophyll and melanin are two examples ofpigments. Chlorophyll gives plants a green color, and melaningives your skin its color.

Color Subtraction Each pigment absorbs at least one colorof light. When you mix pigments together, more colors oflight are absorbed, or subtracted. Therefore, mixing colors ofpigments is called color subtraction.

The primary pigments are yellow, cyan, and magenta. Theycan be combined to produce any other color. In fact, all thecolors in this book were produced by using just the primarypigments and black ink. The black ink was used to providecontrast to the images. Figure 27 shows how the four pigmentscombine to produce many different colors.

Figure 27 The picture of the balloon onthe left was made by overlapping yellowink, cyan ink, magenta ink, and black ink.

The Nature of Light 585Copyright © by Holt, Rinehart and Winston. All rights reserved.

REVIEW


Minerals are naturally occurring crys-talline solids. A blue mineral calledazurite was once used by Europeanpainters as a pigment in paint. Butthese painters didn’t realize that azu-rite changes into another mineralover time. The new mineral, mala-chite, is green. So some paintingsthat once had beautiful blue skiesnow have skies that look greenish.

1. Describe three different ways light interacts with matter.

2. What are the primary colors of light, and why are theycalled primary colors?

3. Describe the difference between the primary colors oflight and the primary pigments.

4. Applying Concepts Explain what happens to the dif-ferent colors of light when white light shines on a vio-let object.

Yellow

Cyan

Magenta

Black

NSTA

TOPIC: ColorsGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP550

Chapter 22586

SECTION 1 SECTION 2

Vocabularyelectromagnetic wave (p. 564)

radiation (p. 565)

Section Notes

• Light is an electromagnetic(EM) wave. An electromag-netic wave is a wave thattravels as vibrating electricand magnetic fields. EMwaves require no mediumthrough which to travel.

• Electromagnetic waves areproduced by the vibration ofelectrically charged particles.

• The speed of light in avacuum is 300,000,000 m/s.

Vocabularyelectromagnetic spectrum(p. 567)

Section Notes

• All EM waves travel at thespeed of light. EM waves dif-fer only by wavelength andfrequency.

• The entire range of EMwaves is called the electro-magnetic spectrum.

• Radio waves are most oftenused for communication.

• Microwaves are used forcooking and in radar.

• Infrared waves have shorterwavelengths and higher fre-quencies than microwaves.The absorption of infraredwaves is felt as an increase in temperature.

• Visible light is the verynarrow range of wavelengthsthat humans can see. Dif-ferent wavelengths are seenas different colors.

• Ultraviolet light is useful forkilling bacteria and for pro-ducing vitamin D in thebody, but overexposure cancause health problems.

• X rays and gamma rays areEM waves that are often usedin medicine. Overexposureto these EM waves can dam-age or kill living cells.

Skills CheckMath ConceptsDISTANCE To calculate the distance that lighttravels in space, multiply the amount of time lighttravels by the speed of light in a vacuum. Thespeed of light in a vacuum is 300,000,000 m/s. Iflight from a star travels for 192 seconds beforereaching a planet, then the distance the light trav-eled can be calculated as follows:

distance speed of light time

distance 300,000,000 m/s 192 s

distance 57,600,000,000 m

Visual UnderstandingTHE PRODUCTION OF LIGHT Light is producedby the vibration of electrically charged parti-cles. Repeated vibrations of these particles, orelectrons, release tiny “packets” of energy calledphotons. Review Figure 2 on page 565 to seehow light and other electromagnetic waves arethe result of electron movement.

Chapter Highlights


SECTION 3


law of reflection (p. 575)

absorption (p. 576)

scattering (p. 577)

refraction (p. 577)



Section Notes

• Two types of reflection areregular and diffuse reflection.

• Absorption and scatteringcause light beams to becomedimmer with distance.

• How much a light beam bendsduring refraction depends onthe light’s wavelength.

• Light waves diffract morewhen traveling through anarrow opening.

• Interference of light wavescan cause bright and darkbands.

Vocabularytransmission (p. 581)

transparent (p. 582)

translucent (p. 582)

opaque (p. 582)

pigment (p. 584)

Section Notes

• Objects are classified astransparent, translucent, oropaque depending on theirability to transmit light.

• Colors of opaque objects aredetermined by the color oflight they reflect. Whiteopaque objects reflect all col-ors and black opaque objectsabsorb all colors.

• Colors of transparent and translucent objects are determined by the color of light they transmit. All other colors are absorbed.

• White light is a mixture ofall colors of light. The pri-mary colors of light are red,blue, and green.

• Pigments give objects color.The primary pigments aremagenta, cyan, and yellow.

LabsWhat Color of Light Is Best for

Green Plants? (p. 716)

Which Color Is Hottest? (p. 717)

Mixing Colors (p. 718)

SECTION 4


TOPIC: Using Light sciLINKS NUMBER: HSTP528

TOPIC: Light Energy sciLINKS NUMBER: HSTP529

TOPIC: The Electromagnetic Spectrum sciLINKS NUMBER: HSTP530

TOPIC: Reflection and Refraction sciLINKS NUMBER: HSTP545

TOPIC: Colors sciLINKS NUMBER: HSTP550



KEYWORD: HSTLGT

587The Nature of LightCopyright © by Holt, Rinehart and Winston. All rights reserved.



1. ? is the transfer of energy by electro-magnetic waves. (Radiation or Scattering)

2. This book is a(n) ? object. (translucentor opaque)

3. ? is a wave interaction that occurswhen two or more waves overlap andcombine. (Diffraction or Interference)

4. Light is a type of ? . (electromagneticwave or electromagnetic spectrum)

5. Light travels through an object during ? . (absorption or transmission)


Multiple Choice

6. Electromagnetic waves transmit a. charges. c. matter.b. fields. d.energy.

7. Objects that transmit light easily area. opaque. c. transparent.b. translucent. d.colored.

8. You can see yourself in a mirror because ofa. absorption. c. regular reflection.b. scattering. d. diffuse reflection.

9. Shadows have blurry edges because of a. diffuse reflection. c. diffraction.b. scattering. d. refraction.

10. Microwaves are often used fora. cooking.b. broadcasting AM radio.c. cancer treatment.d.All of the above

11. What color of light is produced when redlight is added to green light?a. cyan c. yellowb. blue d.white

12. Prisms produce rainbows througha. reflection. c. diffraction.b. refraction. d. interference.

13. Which type of electromagnetic wave travels the fastest in a vacuum?a. radio wavesb. visible lightc. gamma raysd.They all travel at the same speed.

14. Electromagnetic waves are made ofa. vibrating particles.b. vibrating charged particles.c. vibrating electric and magnetic fields.d.electricity and magnetism.

Short Answer

15. Name two ways EM waves differ from oneanother.

16. Describe how an electromagnetic wave isproduced.

17. Why is it difficult to see through glassthat has frost on it?

588 Chapter 22Copyright © by Holt, Rinehart and Winston. All rights reserved.

Concept Mapping

18. Use the followingterms to create aconcept map: light,matter, reflection,absorption, scattering,transmission.


19. A tern is a type of bird that dives under-water to catch fish. When a young ternbegins learning to catch fish, it is rarelysuccessful. The tern has to learn thatwhen a fish appears to be in a certainplace underwater, the fish is actually in aslightly different place. Explain why thetern sees the fish in the wrong place.

20. Radio waves and gamma rays are bothtypes of electromagnetic waves. Exposureto radio waves does not harm the humanbody, whereas exposure to gamma rayscan be extremely dangerous. What is thedifference between these types of EMwaves? Why are gamma rays moredangerous?

21. If you look around a parking lot duringthe summer, you might notice sun shadesset up in the windshields of cars. Explainhow the sun shades help keep the insideof a car cool.

MATH IN SCIENCE

22. Calculate the time it takes for light fromthe sun to reach Mercury. Mercury is54,900,000,000 m away from the sun.


23. Each of the pictures below shows theeffects of a wave interaction of light.Identify the interaction involved.

a

b

c




ReadingCheck-up


590

Fireflies Light the Way

Just as beams of light from coastal light-houses warn boats of approaching dan-ger, scientists are using the light of an

unlikely source—fireflies—to warn food inspec-tors of life-threatening bacterial contamination!Thousands of people die each year from meatcontaminated with bacteria. The light from fire-flies is being used to study several diseases,waste-water treatment, and environmentalprotection as well!

Nature’s Guiding LightA number of organisms, including some fishes,squids, beetles, and bacteria, emit light. Fire-flies, in particular, use this light to attract mates.How do these organisms use energy to emitlight?

Remarkably, all of these organisms use one enzyme to make light, an enzyme calledluciferase. This enzyme breaks down adenosinetriphosphate (ATP) to create energy. This energyis used to excite electrons to produce light inthe form of a glow or flash. Fireflies are veryeffective light bulbs. Nearly 100 percent of theenergy they get from ATP is given off as light.Only 10 percent of energy given off by electri-cal light bulbs is in the form of light; the other 90 percent is thermal energy!

Harnessing Life’s LightHow have scientists harnessed the firefly’s abilityto produce light to find bacteria? Researchershave found the gene responsible for makingluciferase. Scientists have taken the gene fromfireflies that makes luciferase and inserted it intoa virus that preys on bacteria. The virus isn’tharmful to humans and can be mixed into meatto help scientists detect bacteria. When the virusinfects the bacteria, it transfers the gene into thegenetic machinery of the bacteria. This bacteriathen produces luciferase and glows!

This process is being used to find a numberof dangerous bacteria that contaminate foods,including Salmonella and Escherichia coli.These bacteria are responsible for thousands ofdeaths each year. Not only is the test effective,it is fast. Before researchers developed this test,it took up to 3 days to determine whether food wascontaminated bybacteria. By thattime, the foodwas already at the grocery store!

Think About It! What color of light would you hypothesizegives plants the most energy? Investigate, andsee if your hypothesis is right!

The firefly (Photuris pyralis) is helping foodinspectors save thousands of lives each year!


591

It’s a Heat Wave!

Percy L. Spencer never stopped looking foranswers. In fact, he patented 120 inven-tions in his 39 years with the company

Raytheon. During a routine visit to one of theRaytheon laboratories in 1946, Spencer foundthat a candy bar had meltedinside his coat pocket. Hecould have just chalked thisup to body heat, but hedidn’t. Instead, he took acloser look at his surround-ings and noticed a nearbymagnetron—a tube he de-signed to produce micro-waves for radar systems.

A Popping TestThis made Spencer curious.Did the microwaves from themagnetron melt the candybar, and if so, could micro-waves be used to heat otherthings? Spencer answered hisquestions by putting a bag ofunpopped corn kernels nextto a magnetron. The kernels popped! Spencerhad just made the first “microwave” popcorn!The test was a huge success. This simple experi-ment showed that a magnetron could heat foodswith microwaves, and it could heat them quickly.When Spencer patented his invention in 1953, he called it a “High Frequency Dielectric HeatingApparatus.”

Perfect Timing!Spencer originally designed magnetrons for radarmachines used in World War II. Discoveringanother use for them was well timed. After thewar, the military had little use for the 10,000 mag-netrons a week that Raytheon could manufacture.So Raytheon decided to use the magnetrons topower Spencer’s “High Frequency Dielectric

Heating Apparatus.” But first the company had tocome up with a simpler name! The winning entryin the renaming contest was “Radar Range,” whichlater became one word, Radarange.

An InconvenientConvenienceThe first Radaranges had afew drawbacks. For one thing,they were very expensive.They also weighed over 340 kg and were 1.6 m tall.Try fitting that on your kit-chen counter! Because theRadarange was so large andexpensive, only restaurants,railroad companies, and cruiseships used them. By 1967,improvements in the designmade the Radarange compactand affordable, similar to themicrowave ovens of today.

Now You’reCooking!

Just how do microwave ovens cook food? It justso happens that microwaves are absorbed bywater molecules in the food being cooked.When water molecules throughout the foodabsorb microwaves, they start to move faster.As a result, the food’s temperature increases.Leftovers anyone?

Find Out for Yourself Microwaves make water molecules in foodmove faster. This is what increases the tempera-ture of food that is cooked in a microwave. Butdid you know that most dishes will not heat upin a microwave oven if there is no food onthem? To discover why, find out what mostdishes are made of. Then infer why emptydishes do not heat up in a microwave.

The first microwave oven, known as a“Radarange,” 1953


592 Chapter 23

Light Sources . . . . . . 594Astronomy Connection . . . . . . . . 594


Mirrors and Lenses . . 598Apply . . . . . . . . . . . . . 602Internet Connect . . . . 602Internet Connect . . . . 604

Light and Sight . . . . . 605Biology Connection . . 607Internet Connect . . . . 607

Light Technology . . . . 608QuickLab . . . . . . . . . . 613Internet Connect . . . . 613

Chapter Review . . . . . . . . . 616


LabBook . . . . . . . . . . 720–723

Light andOur WorldLight andOur World

Bright Lights, Neon LightsLook at the multicolored arcs of light in this photo. These“neon” lights are made by passing electric current throughtubes filled with certain gases. Neon, argon, krypton, helium,and mercury gases each light up as a different dazzlingcolor. In this chapter, you will learn how different kinds oflight are produced and how images that reflect or focuslight are formed. You will also learn how mirrors, lenses,and high-tech instruments focus or transmit light energy.


1. Name three sources oflight.

2. How do mirrors andlenses form images?

3. How does the human eyedetect light?


593

MIRROR, MIRRORIn this activity, you will exploreimages formed by plane mirrors.

Procedure

1. Tape a sheet of graph paper onyour desk. Stand a plane mirrorstraight up in the middle of thepaper. Hold the mirror in place withsmall pieces of modeling clay.

2. Count four grid squares from themirror, and place a pencil there.Look in the mirror. How manysquares behind the mirror is theimage of the pencil? Move thepencil farther away from the mir-ror. How did the image change?

3. Replace the mirror with coloredglass. Look at the pencil image inthe glass. Compare it with theimage you saw in the mirror.

4. Use a pencil to draw a square onthe graph paper in front of theglass. Looking through the glass,trace the image of the square onthe paper behind the glass. Usinga metric ruler, measure and com-pare the sizes of the two squares.

Analysis

5. How does the distance from anobject to a plane mirror comparewith the apparent distance fromthe mirror to the object’s imagebehind the mirror?

6. In general, how does the size ofan object compare with that of itsimage in a plane mirror?

Light and Our WorldCopyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 23594

Light SourcesAlthough visible light represents only a small portion of theelectromagnetic spectrum, it has a huge effect on your life.Visible light from the sun gives plants the energy necessaryfor growth and reproduction. Without plants at the base ofthe food chain, few other life-forms could exist. And of course,without visible light, you could not see anything. Your eyesare totally useless without sources of visible light.

Light Source or Reflection?If you look at a television in a bright room, you see the cabi-net around the television as well as the image on the screen.But if you look at the same television in the dark, only theimage on the screen shows up. The difference is that the screenis a light source, while the cabinet around the television isn’t.

You can see a light source even in the dark because its lightpasses directly into your eyes. Flames, light bulbs, fireflies, andthe sun are all light sources. Scientists describe objects that pro-duce visible light as being luminous (LOO muh nuhs). Figure 1shows examples of luminous objects.

Most of the objects around you are not light sources. Butyou can still see them because light from a light source reflectsoff the objects and then travels to your eyes. Scientists describea visible object that is not a light source as being illuminated(i LOO muh NAYT ed).

Figure 1 Television screens,fires, and fireflies are luminousobjects.

Section

1

luminous neon lightilluminated vapor lightincandescent lightfluorescent light

Compare luminous andilluminated objects.

Name four ways light can beproduced.


Sometimes the moon shines sobrightly that you might think there isa lot of “moonlight.” But did youknow that moonlight is actually sun-light? The moon does not give offlight. You can see the moon becauseit is illuminated by light from thesun. You see different phases of themoon because light from the sunshines only on the part of the moonthat faces the sun.


Producing LightLight sources produce light in many ways. For example, if youheat a piece of metal enough, it will visibly glow red hot. Lightcan also be produced chemically, like the light produced by afirefly. Light can even be produced by sending an electric cur-rent through certain gases.

Incandescent Light If you have ever looked inside a toasterwhile toasting a piece of bread, you may have seen thin wiresor bars glowing red. The wires give off energy as light whenheated to a high temperature. Light produced by hot objectsis called incandescent (IN kuhn DES uhnt) light. Figure 2 showsa source of incandescent light thatyou have in your home.

Sources of incandescent lightalso release a large amount of ther-mal energy. Sometimes this thermalenergy is useful because it can beused to cook food or to warm aroom. But often this thermal energyis not used for anything. For exam-ple, the thermal energy given off by a light bulb is not very useful.

Halogen lights are another typeof incandescent light. They wereoriginally developed for use on thewings of airplanes, but they are now used in homes and in carheadlights. Figure 3 shows howhalogen lights work.

Light and Our World 595

Figure 3 The way in which the tungsten from thefilament can be used over and over again preventsthe bulb from burning out too quickly.

A tungsten fila-ment, heated toabout 3,000°C,glows very brightlyand vaporizes.

The tungsten vapor(red particles) travelsto the glass wall,where it cools toabout 800°C.

At the lower tem-perature, tungstencombines with ahalogen gas (blueparticles) to forma new compound.

The new compound travels backto the filament, where it breaksdown because of the high tem-perature. Tungsten from thecompound is deposited on thefilament and can be used again.

Figure 2 Light bulbs produce incandescent light.

Wires and thefilament carryan electriccurrent.

aElectric currentin the tungstenfilament causesthe filament’stemperature toincrease.

b

c The hot filamentgives off visiblelight and thermalenergy.


Fluorescent Light The light that comes from the long, cylin-drical bulbs in your classroom is called fluorescent light.Fluorescent (FLOO uh RES uhnt) light is visible light emitted bya phosphor particle when it absorbs energy such as ultravioletlight. Fluorescent light is sometimes called cool light becauseless thermal energy is produced than with incandescent light.Figure 4 shows how a fluorescent light bulb works.

Neon Light The visible light emitted by atoms of certain gases,such as neon, when they absorb and then release energy iscalled neon light. Figure 5 shows how neon light is produced.

A true neon light—one in which the tube is filled withneon gas—glows red. Other colors are produced when thetubes are filled with different gases. For example, sodium gasproduces yellow light, and krypton gas produces purple light.A mixture of argon gas and mercury gas produces blue light.

Chapter 23596

Figure 4 Fluorescent Light

Electric current inan electrode causeselectrons to beemitted. The elec-trons travel fromone end of thetube to the other.

The tube is filled with mercuryand argon gases. The electronstransfer energy to mercuryatoms.

Mercury atomsrelease extra energyas ultraviolet light.

The inside of the tube is cov-ered with a substance calledphosphor. When the phos-phor absorbs ultraviolet light,it glows and visible light isproduced.

1 2

3

4

Figure 5 Neon Light

Electric current in an electrodecauses electrons to be emitted.The electrons travel from oneend of the tube to the other.

The tube is filled with gas.The electrons transferenergy to gas particlesduring collisions.

The gas particlesrelease extra energyas visible light.

1 32


Vapor Light Another type of incandescent light, calledvapor light, is produced when electrons combine with gaseousmetal atoms. Street lamps usually contain either mercuryvapor or sodium vapor. You can tell the difference by thecolor of the light. If the light is bluish, the lamp containsmercury vapor. If the light is orange, the lamp containssodium vapor. Both kinds of vapor lamps produce light insimilar ways, as described in Figure 6.

1. Identify five illuminated objects in your classroom, andname the luminous object (or objects) providing the light.

2. Describe places where you might use incandescent light,fluorescent light, neon light, and vapor light.

3. Describe how fluorescent light is similar to neon light.

4. Applying Concepts Halogen bulbs emit bright light from small bulbs. They also emit thermal energy. Would you use a halogen bulb to study by? Why or why not?

REVIEW

Stop! and goread about the

invention oftraffic lights on

page 618.


NSTA

TOPIC: Producing LightGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP555

High-voltage electric current creates an arc of electronsbetween two electrodes.

1

The arc passes through a gascalled xenon, heating the gas to a high temperature.

2

The hot xenon vaporizes sodiumin the tube and causes thesodium atoms to lose electrons.

3

When the electrons recombinewith sodium, light is produced.

4

Figure 6 Sodium vapor lights are verybright and do not produce much glare.



Chapter 23598

Mirrors and LensesLook at the letters on the frontof the ambulance shown atright. Do you notice anythingstrange about them? Some ofthe letters are backward, andthey don’t seem to spell a word.

The letters spell the wordAMBULANCE when viewed ina mirror. Images in mirrors arereversed left to right. The wordambulance is spelled backwardso that people driving cars can readit when they see the ambulance intheir rearview mirror. To understand how images are formedin mirrors, you must first learn how to use rays to trace thepath of light waves.

Rays Show the Path of Light WavesLight is an electromagnetic wave. Light waves travel from theirsource in all directions. If you could trace the path of onewave as it travels away from a light source, you would findthat the path is a straight line. Because light waves travel instraight lines, you can use an arrow called a ray to show thepath and the direction of a light wave. Figure 7 shows some

rays coming from a light bulb.Rays can also be used to show the path of light waves

after the waves have been reflected or refracted.Therefore, rays in ray diagrams are often used to

show changes in the direction light travels afterbeing reflected by mirrors or refracted by lenses.You’ll learn more about ray diagrams a little laterin this section.

Figure 7 Rays from this light bulb show the pathand direction of some light waves produced by the bulb.

plane mirror lensconcave mirror convex lensfocal point concave lensconvex mirror

Illustrate how mirrors and lensesform images using ray diagrams.

Explain the difference betweenreal and virtual images.

Compare plane mirrors, concavemirrors, and convex mirrors.

Explain how concave and convexlenses form images.

Section

2


Mirrors Reflect LightHave you ever looked at your reflection in a metal spoon? Thepolished metal of the spoon acts like a mirror, but not like themirror in your bathroom! If you look on one side of the spoon,your face is upside down. But if you look on the other side,your face is right side up. Why?

The shape of a reflecting surface affects the way light reflectsfrom it. Therefore, the image you see in your bathroom mir-ror differs from the image you see in a spoon. Mirrors are clas-sified by their shape. The different shapes are called plane,concave, and convex.

Plane Mirrors Most mirrors, such as the one in your bath-room, are plane mirrors. A plane mirror is a mirror witha flat surface. When you look in a plane mirror, yourreflection is upright and is the same size as you are.Images in plane mirrors are reversed left to right, asshown in Figure 8.

When you look in a plane mirror, your image appearsto be the same distance behind the mirror as you are in frontof it. Why does your image seem to be behind the mirror?Because mirrors are opaque objects, light does not travel throughthem. But when light reflects off the mirror, your brain inter-prets the reflected light as if it travels in a straight line frombehind the mirror. A virtual image is an image through whichlight does not actually travel. The image formed by a planemirror is a virtual image. The ray diagram in Figure 9 explainshow light travels when you look into a mirror.


Figure 9 The rays show how light reaches your eyes. The dotted lines show where the light appears to come from.

Figure 8 Rearview mirrors incars are plane mirrors.

Your image appearsto be behind themirror because yourbrain assumes thatthe light rays thatenter your eyes travelin a straight linefrom an object toyour eyes.

Light reflects off ofyou and strikes themirror, where it isreflected again. Someof the light reflectingoff the mirror entersyour eyes.


Concave Mirrors Mirrors that are curved inward, such as theinside of a spoon, are called concave mirrors. Because the sur-faces of concave mirrors are curved, the images formed by con-cave mirrors differ from the images formed by plane mirrors.To understand how concave mirrors form images, you mustlearn the terms illustrated in Figure 10.

You already learned that plane mirrors can form only vir-tual images. Concave mirrors also form virtual images, butthey can form real images too. A real image is an image throughwhich light actually passes. A real image can be projected ontoa screen; a virtual image cannot. To find out what kind ofimage a concave mirror forms, you can create a ray diagram.Just remember the following three rules when drawing ray dia-grams for concave mirrors:

600

Is an image real or virtual? Turnto page 720 in the LabBook to

see the difference.

Figure 10 The image formed bya concave mirror depends on itsoptical axis, its focal point, and itsfocal length.

a

b

c

A straight line drawnoutward from the centerof the mirror is calledthe optical axis.

Light beams entering the mirror parallel to the optical axis are reflectedthrough a single point,called the focal point.

The distance betweenthe mirror’s surface andthe focal point is calledthe focal length.

Draw a ray from the top of the object parallel to the optical axis. This ray will reflect through the focal point.

If the object is more than one focal length away fromthe mirror, draw a ray from the top of the objectthrough the focal point. This ray will reflect parallelto the optical axis.

If the object is less than one focal length away fromthe mirror, draw a ray through the top of the objectas if it came from the focal point. This ray will reflectparallel to the optical axis.

1

2

3Chapter 23


Real or Virtual For each ray diagram, you need to draw onlytwo rays from the top of the object to find what kind of imageis formed. If the reflected rays cross in front of the mirror, areal image is formed. The point where the rays cross is the topof the image. If the reflected rays do not cross, trace the reflectedrays in straight lines behind the mirror. Those lines will crossto show where a virtual image is formed. Study Figure 11 tobetter understand ray diagrams.

Neither Real Nor Virtual If an object is placed at the focalpoint of a concave mirror, no image will form. Rule 2 explainswhy this happens—all rays that pass through the focal pointon their way to the mirror will reflect parallel to the opticalaxis. Because all the reflected rays are parallel, they will nevercross in front of or behind the mirror. If you place a lightsource at the focal point of a concave mirror, the light willreflect outward in a powerful light beam. Therefore, concavemirrors are used in car headlights and flashlights.


Figure 11 The type of imageformed by a concave mirrordepends on the distance betweenthe object and the mirror as wellas the focal length.

An object more than one focallength away from a concave mirrorforms an upside-down real image.

An object less than one focal length away from aconcave mirror forms an upright virtual image.The dotted lines show how the reflected rays aretraced behind the mirror to find the virtual image.

Rule 2

Rule 1

Rule 1

Rule 3

Rule 3

Rule 1

Optical axis

Real image Focal point

Optical axis

Focal point

Virtual image


Convex Mirrors If you look at your reflection in the back ofa spoon, you will notice that your image is right side up andsmall. The back of a spoon is a convex mirror—a mirror thatcurves out toward you. Figure 12 shows how an image is formedby a convex mirror. All images formed by convex mirrors arevirtual, upright, and smaller than the original object. Convexmirrors are useful because they produce images of a large area.This is the reason convex mirrors are often used for securityin stores and factories. Convex mirrors are also used as sidemirrors in cars and trucks.

Chapter 23602

Figure 12 All images formed byconvex mirrors are formedbehind the mirror. Therefore, allimages formed by convex mirrorsare virtual.

1. How is a concave mirror different from a convex mirror?

2. Draw a ray diagram showing how a concave mirror formsa real image.

3. Applying Concepts Plane mirrors, concave mirrors, andconvex mirrors are useful at different times. Describe asituation in which you would use each type of mirror.

REVIEW

Convex Mirrors Help Drivers

The passenger side mirrors of most cars and trucks are convex mirrors. Convex mirrors are used because they help the driver see more of the traffic around the car than a plane mirror would.However, these mirrors are often stamped with the words “Objectsin Mirror Are Closer Than They Appear.” What property of convexmirrors makes this warning necessary? Why do you think thewarning is important for drivers?

NSTA

TOPIC: MirrorsGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP560

Optical axis

Virtual image

Focal point


Lenses Refract LightWhat do cameras, binoculars, telescopes, andmovie projectors have in common? They all uselenses to create images. A lens is a curved, trans-parent object that forms an image by refracting,or bending, light. Like mirrors, lenses are clas-sified by their shape. There are two types oflenses—convex and concave.

Convex Lenses A convex lens is thicker in themiddle than at the edges. When light rays entera convex lens, they refract toward the center.Light rays that enter a convex lens parallel tothe optical axis are refracted so that they gothrough a focal point. The amount of refractionand the focal length depend on the curvatureof the lens, as shown in Figure 13. Light rays thatpass through the center of a lens are notrefracted.

Convex lenses form many different kinds ofimages, depending on the focal length of thelens and the position of the object. For exam-ple, whenever you use a magnifying glass, youare using a convex lens to form an enlarged,virtual image. Figure 14 illustrates how a mag-nifying lens works.

603

Figure 13 Light rays refract more through con-vex lenses with greater curvature than throughconvex lenses with less curvature.

Figure 14 If an object is less than one focal lengthaway from a convex lens, a virtual image is formed.The image is larger than the object and can beseen only by looking into the lens.

Optical axis

Focal point

Virtual image


Convex lenses can also form real images. Movie projectorsuse convex lenses to focus real images on a screen. Camerasuse convex lenses to focus real images on a piece of film. Bothtypes of images are shown in Figure 15.

Concave Lenses A concave lens is thin-ner in the middle than at the edges. Lightrays entering a concave lens parallel tothe optical axis always bend away fromeach other toward the edges of the lens;the rays never meet. Therefore, concavelenses can never form a real image.Instead, they form virtual images, asshown in Figure 16. Concave lenses aresometimes combined with other lensesin telescopes. The combination of lensesproduces clearer images of distant objects.You will read about another, more com-mon use for concave lenses in the nextsection.

Chapter 23604

Figure 15 Convex lenses canalso form real images.

If the object is located between one and twofocal lengths away from the lens, a real,enlarged image is formed far away from thelens. This is how movie projectors produceimages on large screens.

If the object is located more than two focallengths away from the lens, a real, reducedimage is formed close to the lens. This is howthe lens of a camera forms images on the film.

Figure 16 Concave lenses form reduced virtualimages. If you trace the refracted rays in a straightline behind a concave lens, you can determine wherethe virtual image is formed.

1. Draw a ray diagram showing how a magnifying glassforms a virtual image.

2. Explain why a concave lens cannot form a real image.

3. Applying Concepts Your teacher sometimes uses an over-head projector to show transparencies on a screen. Whattype of lens does an overhead projector use?

REVIEW

2 focal lengths

1 focal length

2 focal lengths

1 focal length

NSTA

TOPIC: LensesGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP565

Real image

Real image

Virtual image

a b


Light and SightWhen you look around, you can see objects both near andfar. You can also see the different colors of the objects. Yousee luminous objects because they produce their own light,which is detected by your eyes. You see all other objects (illu-minated objects) because light reflecting off the objects entersyour eyes. But how do your eyes work, and what causes peo-ple to have problems with their vision? Read on to find out.

How You Detect LightVisible light is the part of the electromagnetic spectrum thatcan be detected by your eyes. The process by which your eyegathers light to form the images that you see involves severalsteps, as shown in Figure 17.

Figure 17 How Your Eyes Work

e

f

a

b c d

Light is refracted as itpasses through the cornea(KOR nee uh), a transpar-ent membrane that protectsthe eye.

Light then passes throughthe pupil, the opening tothe inside of the eye.

The size of the pupil iscontrolled by the iris,the colored part of theeye. In low light thepupil is large; in brightlight the pupil is small.

The lens of the eye is convex and refracts light to focus a realimage on the back of the eye.Muscles around the lenschange the thickness of thelens so that objects at differentdistances can be seen in focus.

The back surface of the eye iscalled the retina (RET nuh).The light forming the realimage is detected by recep-tors in the retina called rodsand cones.

Nerves attached to therods and cones carry infor-mation to the brain aboutthe light that strikes the retina.

Light from a distant object

Section

3

cornea irispupil retina

Identify the parts of the humaneye, and describe their functions.

Describe some common visionproblems, and explain how theycan be corrected.


Common Vision Problems A person with normal vision can clearly see objects both closeup and far away and can distinguish all colors of visible light.However, because the eye is complex, it’s no surprise thatmany people have defects in their eyes that affect their vision.Luckily, some common vision problems can be easily corrected.

Nearsightedness and Farsightedness The lens of a prop-erly working eye focuses light on the retina, so the imagesformed are always clear. Two common vision problems—near-sightedness and farsightedness—occur when light is not focusedon the retina. A nearsighted person can see objects clearly onlyif the objects are nearby. Objects that are farther away lookblurry. A farsighted person can see faraway objects clearly, butobjects nearby look blurry. Figure 18 explains how nearsight-edness and farsightedness occur and how they can be corrected.

Chapter 23606

Some chickens wear redcontact lenses. The lensesdon’t improve the chickens’vision—they just make thechickens see everything inred! Chickens that see inred are less aggressive andproduce more eggs. But it isdifficult to fit a chicken forcontact lenses properly, andchickens often lose theircontacts quickly.

Figure 18 Nearsightedness and farsightedness are common visionproblems that can be corrected easily with glasses or contact lenses.

Nearsightedness occurs whenthe eye is too long and thelens focuses light in front ofthe retina.

A concave lens placed in front ofthe eye refracts the light outward.The lens in the eye can thenfocus the light on the retina.

Farsightedness occurs whenthe eye is too short and thelens focuses light behind theretina.

A convex lens placed in front ofthe eye refracts the light andfocuses it slightly. The lens in theeye can then focus the light on the retina.


Color Deficiency Roughly 5 to 8 percent of men and 0.5percent of women in the world have color deficiency, oftenreferred to as colorblindness. True colorblindness, in which aperson can see only in black and white, is very rare. The major-ity of people with color deficiency have trouble distinguish-ing shades of red and green, or distinguishing red from green.

Color deficiency occurs when the cones in the retina donot receive the right instructions. The three types of cones arenamed for the colors they detect most—red, green, and blue.Each type of cone reacts to a range of wavelengths of light. Aperson with normal color vision can see all colors. But in somepeople, the cones get the wrong instructions and respond tothe wrong wavelengths. That person may have trouble seeingcertain colors. For example, he or she may see too much redor too much green, and not enough of the other color. Figure 19shows one type of test for color deficiency.


1. Name the parts of the human eye, and describe whateach part does.

2. What kind of lens would help a person who is nearsighted?What kind would help someone who is farsighted?

3. Inferring Conclusions Why do you think colorblindnesscannot be corrected?

4. Applying Concepts Sometimes people are both near-sighted and farsighted. They wear glasses with two dif-ferent kinds of lenses. Why are two lenses necessary?

Figure 19 Doctors use images like these to detect red-green colordeficiency. Can you see a number in each image?

REVIEW

NSTA

TOPIC: The EyeGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP570


Whether a person is colorblinddepends on his or her genes.Certain genes give instructions tothe cones for detecting certainwavelengths of light. If the genesgive the wrong instructions, theperson will have a color deficiency.A person needs one set of thegenes that give the right instruc-tions. Genes for color vision are onthe X chromosome. Women havetwo X chromosomes, but men haveonly one. Therefore, men are morelikely to be lacking a set of thesegenes and are more likely thanwomen to be colorblind.



Figure 20 The Parts of a Camera

Chapter 23608

Light TechnologySo far in this chapter, you have learned some ways light canbe produced, how mirrors and lenses affect light, and someways that people use mirrors and lenses. In this section, youwill learn how different technological devices rely on mirrorsand lenses and how mirrors help produce a type of light calledlaser light.

Optical InstrumentsOptical instruments are devices that use arrangements of mir-rors and lenses to help people make observations. Some opti-cal instruments help you see objects that are very far away,and some help you see objects that are very small. Some optical instruments record images. The optical instrument thatyou are probably most familiar with is the camera.

Cameras The way a camera works is similar to the way youreye works. A camera has a lens that focuses light and has anopening that lets in light. The main difference between a cam-era and the eye is that the film in a camera permanently storesthe images formed on it, but the images formed on the retinadisappear when you stop looking at an object. Figure 20 showsthe parts of a camera and their functions.

The shutter opens and closesbehind the lens to control howmuch light enters the camera.The longer the shutter is open, the more light enters the camera.

The lens of a camera is a convexlens that focuses light on the film.Moving the lens focuses light fromobjects at different distances.

The film is coated withchemicals that react whenthey are struck by light.The result is an imagestored on the film.

The aperture is an opening in thelens that lets light into the camera.The larger the aperture is, the morelight enters the camera.

Section

4

laser hologram

Explain how optical instrumentsuse lenses and mirrors to formimages.

Explain how lasers work andwhat makes laser light differentfrom non-laser light.

Identify uses for lasers. Describe how optical fibers and

polarizing filters work.


Telescopes Astronomers use telescopes to study objects inspace, such as the moon, planets, and stars. Telescopes are clas-sified as either refracting or reflecting. Refracting telescopes uselenses to collect light, while reflecting telescopes use mirrors.Figure 21 illustrates how simple refracting and reflecting tele-scopes work.

Light Microscopes Simple light microscopes are similar torefracting telescopes. They have two convex lenses—an objec-tive lens, which is close to the object being studied, and aneyepiece lens, which you look through. The difference betweenmicroscopes and telescopes is that microscopes are used to seemagnified images of tiny, nearby objects rather than imagesof large, distant objects.

Lasers and Laser LightHave you ever seen a laser light show? Laser light beams flashthrough the air and sometimes form pictures on surfaces. Alaser is a device that produces intense light of only one colorand wavelength. Laser light is different from non-laser lightin many ways. One important difference is that laser light iscoherent. When light is coherent, light waves move together asthey travel away from their source. The crests and troughs ofcoherent light waves line up, and the individual waves behaveas one single wave. Other differences between laser light andnon-laser light are shown in Figure 22, on the next page.


Figure 21 Both refracting andreflecting telescopes are used tosee objects that are far away.

Concave mirror

Eyepiece lens

Planemirror

Objective lens

Eyepiece lens

A reflecting telescope has a concave mirrorthat collects and focuses light to form a realimage. The light strikes a plane mirror thatdirects the light to the convex eyepiecelens, which magnifies the real image.

A refracting telescope has two convex lenses.Light enters through the objective lens and formsa real image. This real image is then magnifiedby the eyepiece lens. You see this magnifiedimage when you look through the eyepiece lens.

Self-CheckExplain why the objec-tive lens of a telescopecannot be a concavelens. (See page 724 tocheck your answer.)


How Lasers Produce Light The word laser stands for lightamplification by stimulated emission of radiation. You alreadyknow what light and radiation are. Amplification is the increasein the brightness of the light.

What is stimulated emission? In an atom, an electron canmove from one energy level to another. A photon is releasedwhen an electron moves from a higher energy level to a lowerenergy level. This process is called emission. Stimulated emis-sion occurs when a photon strikes an atom in an excited stateand makes that atom emit another photon. The newly emit-ted photon is identical to the first photon, and they travelaway from the atom together. Figure 23 shows how stimulatedemission works to produce laser light.

Chapter 23610

Figure 22 Laser Light Versus Non-laser Light

Figure 23 A Helium-Neon Laser

Laser light is tightly focusedand does not spread out verymuch over long distances. Laserlight contains light waves ofonly one wavelength and color.

Non-laser light spreads outgreatly even over short distances.It may contain light waves of manydifferent wavelengths and colors.

a

d

The inside of the laser is filled with heliumand neon gases. An electric current in thegases excites the atoms of the gases.

Excited neon atoms release photons of redlight. When these photons strike other excitedneon atoms, stimulated emission occurs.

Plane mirrors on both ends ofthe laser reflect photons trav-eling the length of the laserback and forth along the tube.

Because the photonstravel back and forth manytimes, many stimulatedemissions occur, makingthe laser light brighter.

One mirror is onlypartially coated, sosome of the photons“leak” out and forma laser light beam.

b

c e



Holograms Lasers are used to produce holograms. A hologramis a piece of film on which an interference pattern produces a three-dimensional image of an object. You have probably seenholograms on magazine covers or baseball cards. Figure 24shows how light from a laser is split into two beams. Thesetwo beams combine to form an interference pattern on thefilm, which results in a hologram.

Holograms, like the one shown in Figure 25, are similar tophotographs because they are images permanently recorded onfilm. However, unlike photographs, the images you see are noton the surface of the film. They appear eitherin front of or behind the film. And ifyou move the image around, youwill see it from different angles.

Other Uses for Lasers Inaddition to making holo-grams, lasers are used for awide variety of tasks. Forexample, lasers are used tocut materials such as metaland cloth. Surgeons some-times use lasers to cutthrough human tissue. Lasersurgery on the cornea of theeye can correct nearsighted-ness and farsightedness. And,as you read at the beginning ofthis chapter, lasers can also be usedas extremely accurate rulers. You evenuse a laser when you listen to music froma CD player.

Mirror

Beam 1

Beam splitter Laser

Mirror

Beam 2

LensFilm

Object

Lens

Figure 24 Light from one beamshines directly on the film, andlight from the other beam shineson an object and is reflected ontothe film.

Figure 25 After the film is developed, the interference pattern reconstructs a three-dimensional image of the object.


Fiber OpticsImagine a glass thread as thin as a human hair that can trans-mit more than 1,000 telephone conversations at the same timewith only flashes of light. It might sound impossible, but suchglass threads are at work all over the world. These threads,called optical fibers, are thin, flexible glass wires that can trans-mit light over long distances. Some optical fibers are shownat left. The use of optical fibers is called fiber optics. The trans-mission of information through telephone cables is the mostcommon use of fiber optics. Optical fibers carry informationfaster and more clearly than older copper telephone cables.Optical fibers are also used to network computers and to allowdoctors to see inside patients’ bodies without performing major surgery.

Light in a Pipe Optical fibers transmit light over long dis-tances because they act like pipes for light. Just as a good waterpipe doesn’t let water leak out, a good light pipe doesn’t letlight leak out. Light stays inside an optical fiber because of totalinternal reflection. Total internal reflection is the complete reflec-tion of light along the inside surface of the medium throughwhich it travels. Figure 26 shows total internal reflection in anoptical fiber.

Polarized LightNext time you go shopping for sunglasses, look for those thathave lenses that polarize light. Sunglasses that contain polar-izing lenses reduce glare better than sunglasses that do not.Polarized light consists of light waves that vibrate in only oneplane. Figure 27 illustrates how light is polarized.

Chapter 23612

Figure 26 As light travelsthrough an optical fiber, itreflects off the sides thousandsof times each meter.

Figure 27 Light waves travel in all directions.Polarizing filters have long molecules that lineup like parallel slits. When light waves strikea polarizing filter, only the waves vibrating inthe same direction as the slits pass through.

Polarizing filter

Polarized light


When light reflects at a certain angle from a smooth sur-face, it is completely polarized parallel to that surface. If thesurface is parallel to the ground, the light is polarized hori-zontally. This is what causes the bright glare from bodies ofwater and car hoods.

Polarizing sunglasses reduce glare from horizontal surfacesbecause the sunglasses have lenses with vertically polarized fil-ters. These filters allow only vertically vibrating light waves topass through them. So when you wear polarizing sunglasses,the reflected light that is horizontally polarized does not reachyour eyes. Polarizing filters are also used by photographers toreduce glare and reflection in their photographs. ExamineFigure 28 to see the effect of a polarizing filter on a camera.


1. How is a camera similar to the human eye?

2. What is the difference between a refracting telescope anda reflecting telescope?

3. How is a beam of laser light different from non-laser light?

4. Why are fiber optics useful for transmitting information?

5. Applying Concepts Why do you think lasers are usedto cut cloth and metal and to perform surgery?

REVIEW

Figure 28 These two photos were taken by the same camera fromthe same angle. There is less reflected light in the photo at rightbecause a polarizing filter was placed over the lens of the camera.

Now You See, Now You Don’t

1. Hold a lens from a pairof polarizing sunglassesup to your eye, and lookthrough it. Describe yourobservations in yourScienceLog.

2. Put a second polarizinglens over the first lens.Make sure both lenses areright side up. Look throughboth lenses, and describeyour observations in yourScienceLog.

3. Rotate one lens slowly asyou look through bothlenses, and describe whathappens.

4. Why can’t you see throughthe lenses when they arelined up a certain way?Record your answer inyour ScienceLog.

NSTA

TOPIC: LasersGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP575

Chapter Highlights

Chapter 23614

SECTION 1 SECTION 2

Vocabularyluminous (p. 594)

illuminated (p. 594)

incandescent light (p. 595)

fluorescent light (p. 596)

neon light (p. 596)

vapor light (p. 597)

Section Notes

• You see objects eitherbecause they are luminous(produce their own light) orbecause they are illuminated(reflect light).

• Light produced by hotobjects is incandescent light.Ordinary light bulbs are acommon source of incandes-cent light.

• Fluorescent light is visiblelight emitted by a particlewhen it absorbs ultravioletlight. Little energy is wastedby fluorescent light bulbs.

• Neon light results from anelectric current in certaingases.

• Vapor light is producedwhen electrons combinewith gaseous metal atoms.

Vocabularyplane mirror (p. 599)

concave mirror (p. 600)

focal point (p. 600)

convex mirror (p. 602)

lens (p. 603)

convex lens (p. 603)

concave lens (p. 604)

Section Notes• Rays are arrows that show the

path and direction of a singlelight wave. Ray diagrams canbe used to determine whereimages are formed by mirrorsand lenses.

• Plane mirrors produce virtualimages that are the same sizeas the objects. These imagesare reversed left to right.

Skills CheckVisual UnderstandingOPTICAL AXIS, FOCAL POINT, AND FOCALLENGTH To understand how concave and con-vex mirrors and lenses work, you need to knowwhat the terms optical axis, focal point, and focallength mean. Figure 10 on page 600 explainsthese terms.

LASERS Laser light is different from ordinarynon-laser light in several ways. Look back atFigure 22 on page 610 to review some differ-ences between the two types of light.

THE EYE Study Figure 17 on page 605 toreview the parts of the eye and review the process by which your eye gathers light to form the images that you see.


SECTION 3SECTION 2 SECTION 4

• Concave mirrors can producereal images and virtualimages. They can also be usedto produce a powerful lightbeam.

• Convex mirrors produce onlyvirtual images.

• Convex lenses can producereal images and virtualimages. A magnifying glass isan example of a convex lens.

• Concave lenses produce onlyvirtual images.

LabsMirror Images (p. 720)

Images fromConvex Lenses (p. 722)

Vocabularycornea (p. 605)

pupil (p. 605)

iris (p. 605)

retina (p. 605)

Section Notes

• Your eye has several parts,such as the cornea, the pupil,the iris, the lens, and theretina.

• Nearsightedness and farsight-edness occur when light isnot focused on the retina.Both problems can be cor-rected with glasses or contactlenses.

• Color deficiency is a geneticcondition in which cones inthe retina are given the wronginstructions. Color deficiencycannot be corrected.

Vocabularylaser (p. 609)

hologram (p. 611)

Section Notes

• Optical instruments, such as cameras, telescopes, andmicroscopes, are devices that use mirrors and lenses to help people make observations.

• Lasers are devices that pro-duce intense, coherent lightof only one wavelength andcolor. Lasers produce light bya process called stimulatedemission.

• Optical fibers can transmitlight over long distancesbecause of total internalreflection.

• Polarized light contains lightwaves that vibrate in onlyone direction.


TOPIC: Producing Light sciLINKS NUMBER: HSTP555

TOPIC: Mirrors sciLINKS NUMBER: HSTP560

TOPIC: Lenses sciLINKS NUMBER: HSTP565

TOPIC: The Eye sciLINKS NUMBER: HSTP570

TOPIC: Lasers sciLINKS NUMBER: HSTP575



KEYWORD: HSTLOW

615Light and Our WorldCopyright © by Holt, Rinehart and Winston. All rights reserved.



1. ? is commonly used in homes andproduces a lot of thermal energy.(Incandescent light or Fluorescent light)

2. A ? is curved inward, like the insideof a spoon. (convex mirror or concave mirror)

3. You can see an object when light isfocused on the ? of your eye. (pupil orretina)

4. A ? is a device that produces coherent,intense light of only one color. (laser or lens)

5. You can see this book because it is a(n) ? object. (luminous or illuminated)


Multiple Choice

6. When you look at yourself in a planemirror, you see aa. real image behind the mirror.b. real image on the surface of the mirror.c. virtual image that appears to be behind

the mirror.d.virtual image that appears to be in front

of the mirror.

7. A vision problem that occurs when lightis focused in front of the retina isa. nearsightedness.b. farsightedness.c. color deficiency.d.None of the above

8. Which part of the eye refracts light?a. iris c. lensb. cornea d.both (b) and (c)

9. Visible light produced when electronscombine with gaseous metal atoms isa. incandescent light.b. fluorescent light.c. neon light.d.vapor light.

10. You see less of a glare when you wearcertain sunglasses because the lensesa. produce total internal reflection.b. create holograms.c. produce coherent light.d.polarize light.

11. What kind of mirrors provide images oflarge areas and are used for security?a. plane mirrors c. convex mirrorsb. concave mirrors d.all of the above

12. A simple refracting telescope hasa. a convex lens and a concave lens.b. a concave mirror and a convex lens.c. two convex lenses.d. two concave lenses.

13. Light waves in a laser beam interact andact as one wave. This light is calleda. red. c. coherent.b. white. d.emitted.

Short Answer

14. What type of lens should be prescribedfor a person who cannot focus on nearbyobjects? Explain.

15. How is a hologram different from aphotograph?

16. Why might a scientist at the North Poleneed polarizing sunglasses?


Concept Mapping

17. Use the followingterms to create aconcept map: lens,telescope, camera, realimage, virtual image,optical instrument.


18. Stoplights are usually mounted so that thered light is on the top and the green lightis on the bottom. Explain why it is impor-tant for a person who has red-green colordeficiency to know this arrangement.

19. Some companies are producing fluores-cent light bulbs that will fit into socketson lamps designed for incandescentlight bulbs. Although fluorescent bulbsare more expensive, the companies hopethat people will use them because theyare better for the environment. Explainwhy fluorescent light bulbs are better forthe environment than incandescentlight bulbs.

20. Imagine you are given a small device thatproduces a beam of red light. You want tofind out if the device is producing laserlight or if it is just a red flashlight. To dothis, you point the beam of light against a wall across the room. What would youexpect to see if the device is producinglaser light? Explain.


21. Examine the ray diagrams below, andidentify the type of mirror or lens that isbeing used and the kind of image that isbeing formed.


a

b

c



ReadingCheck-up


618

One day in the 1920s, an automobile col-lided with a horse and carriage. The rid-ers were thrown from their carriage, the

driver of the car was knocked unconscious, andthe horse was fatally injured. A man namedGarrett Morgan (1877–1963) witnessed thisscene, and the accident gave him an idea.

A Bright IdeaMorgan’s idea was a signal that included signsto direct traffic at busy intersections. The signalcould be seen from a distance and could beclearly understood.

Morgan patented the first traffic signal in1923. His signal looked very different fromthose used today. Unlike the small, three-bulbsignal boxes that now hang over most busyintersections, the early versions were T-shaped,with the words stop and go printed on them.

Morgan’s traffic signal was operated by apreset timing system. An electric motor turneda system of gears that operated a timing dial.As the timing dial rotated, it turned theswitches on and off.

Morgan’s invention was an immediate suc-cess, and he sold the patent to General ElectricCorporation for $40,000—quite a large sum inthose days. Since then, later versions ofMorgan’s traffic signal have been the mainstayof urban traffic control.

Light TechnologyThe technology of traffic lights continues toimprove. For example, in some newer modelsthe timing can be changed, depending on thetraffic needs for a particular time of day. Somemodels have sensors installed in the street tomonitor traffic flow. In other models, sensors canbe triggered from inside an ambulance so thatthe light automatically turns green, allowing theambulance to pass.

More AboutMorganGarrett Morgan, theson of former slaves,was born in Paris,Kentucky. He was oneof 11 children, and hisformal education endedat the sixth grade. At age14, with no money andfew skills, Morgan left hometo work in Cincinnati, Ohio. Hesoon moved to Cleveland and quickly taught him-self enough about sewing machines to get a jobrepairing them. Morgan saw how important therest of his education was, so he taught himselfand he hired tutors to help him complete hiseducation. By 1907, Morgan opened his ownsewing-machine repair shop. He was on his way!

Not only was Morgan an inventor, he was a hero. Gas masks that Morgan invented in 1912were used in WWI to protect soldiers from chlorine gas fumes. Morgan himself, wearingone of his masks, later helped save several men trapped in a tunnel after a gas explosion.

Think About It Traffic control is not the only system in which light is used as a signal. What aresome other systems that do so, and whatmakes light so useful for communication?

Traffic Lights

Morgan's patent for the first traffic light


Many of these strategies also save money bysaving energy.

Astronomers hope that public awarenesswill help improve the visibility of the night skyin and around major cities. Some cities, includ-ing Boston and Tucson, have already madesome progress in reducing light pollution.Scientists have projected that if left unchecked,light pollution will affect every observatory onEarth within the next decade.

See for Yourself With your parents’ permission, go outside atnight and find a place where you can see thesky. Count the number of stars you cansee. Now turn on a flashlight or porchlight. How many stars can you seenow? Compare your results. Howmuch was your visibility reduced?

619

Light PollutionAt night, large cities are oftenvisible from far away. Soft lightfrom windows outlines buildings.Bright lights from stadiums andparking lots shine like beacons.Scattered house lights twinklelike jewels. The sight is stunning!

Unfortunately, astronomers consider allthese lights a form of pollution. Around theworld, light pollution is reducing astronomers’ability to see beyond our atmosphere.

Sky GlowTwenty years ago, stars were very visible aboveeven large cities. The stars are still there, butnow they are obscured by city lights. Thisglow, called sky glow, is created when lightreflects off dust and other particles suspendedin the atmosphere. Sky glow affects the entireatmosphere to some degree. Today, evenremote locations around the globe are affectedby light pollution.

The majority of light pollution comes fromoutdoor lights such as headlights, street lights,porch lights, and bright parking-lot and sta-

dium lights. Other sources include forestfires and gas burn-offs in oil fields. Air pol-

lution makes the situation worse, addingmore particles to the air so that reflection is

even greater.

A Light of HopeUnlike other kinds of pollution, light pollutionhas some simple solutions. In fact, light pollu-tion can be reduced in as little time as it takesto turn off a light! While turning off most citylights is impractical, several simple strategiescan make a surprising difference. For example,using covered outdoor lights keeps the lightangled downward, preventing most of the

light from reaching particles in the sky. Also,using motion-sensitive lights and timedlights helps eliminate unnecessary light.

Lights from cities can be seen from space, asshown in this photograph taken from the space shuttle Columbia. Bright, uncoveredlights (inset) create a glowing haze in the nightsky above most cities in the United States.



LabBook 621

Safety First! . . . . . . . . . . . . . . . . . . . . . 622

Chapter 1 The World of Physical ScienceExploring the Unseen . . . . . . . . . . . . . . . . . 626Off to the Races! . . . . . . . . . . . . . . . . . . . . . 627Measuring Liquid Volume . . . . . . . . . . . . . . 628Coin Operated . . . . . . . . . . . . . . . . . . . . . . . 629

Chapter 2 The Properties of MatterVolumania! . . . . . . . . . . . . . . . . . . . . . . . . . 630Determining Density . . . . . . . . . . . . . . . . . . 632Layering Liquids . . . . . . . . . . . . . . . . . . . . . 633White Before Your Eyes . . . . . . . . . . . . . . . . 634

Chapter 3 States of MatterFull of Hot Air! . . . . . . . . . . . . . . . . . . . . . . 636Can Crusher . . . . . . . . . . . . . . . . . . . . . . . . 637A Hot and Cool Lab . . . . . . . . . . . . . . . . . . 638

Chapter 4 Elements, Compounds, and Mixtures

Flame Tests . . . . . . . . . . . . . . . . . . . . . . . . . 640A Sugar Cube Race! . . . . . . . . . . . . . . . . . . . 642Making Butter . . . . . . . . . . . . . . . . . . . . . . . 643Unpolluting Water . . . . . . . . . . . . . . . . . . . 644

Chapter 5 Matter in MotionBuilt for Speed . . . . . . . . . . . . . . . . . . . . . . 646Detecting Acceleration . . . . . . . . . . . . . . . . 647Science Friction . . . . . . . . . . . . . . . . . . . . . . 650Relating Mass and Weight . . . . . . . . . . . . . . 651

Chapter 6 Forces in MotionA Marshmallow Catapult . . . . . . . . . . . . . . . 652Blast Off! . . . . . . . . . . . . . . . . . . . . . . . . . . . 653Inertia-Rama! . . . . . . . . . . . . . . . . . . . . . . . 654Quite a Reaction . . . . . . . . . . . . . . . . . . . . . 656

Chapter 7 Forces in FluidsFluids, Force, and Floating . . . . . . . . . . . . . 658Density Diver . . . . . . . . . . . . . . . . . . . . . . . 660Taking Flight . . . . . . . . . . . . . . . . . . . . . . . . 661

Chapter 8 Work and MachinesA Powerful Workout . . . . . . . . . . . . . . . . . . 662Inclined to Move . . . . . . . . . . . . . . . . . . . . . 664Building Machines . . . . . . . . . . . . . . . . . . . 665Wheeling and Dealing . . . . . . . . . . . . . . . . . 666

Chapter 9 Energy and Energy ResourcesFinding Energy . . . . . . . . . . . . . . . . . . . . . . 668Energy of a Pendulum . . . . . . . . . . . . . . . . . 670Eggstremely Fragile . . . . . . . . . . . . . . . . . . . 671

Chapter 10 Heat and Heat TechnologyFeel the Heat . . . . . . . . . . . . . . . . . . . . . . . . 672Save the Cube! . . . . . . . . . . . . . . . . . . . . . . 674Counting Calories . . . . . . . . . . . . . . . . . . . . 675

ContentsChapter 11 Introduction to Atoms

Made to Order . . . . . . . . . . . . . . . . . . . . . . . 676

Chapter 12 The Periodic TableCreate a Periodic Table . . . . . . . . . . . . . . . . 678

Chapter 13 Chemical BondingCovalent Marshmallows . . . . . . . . . . . . . . . 680

Chapter 14 Chemical ReactionsFinding a Balance . . . . . . . . . . . . . . . . . . . . 682Cata-what? Catalyst! . . . . . . . . . . . . . . . . . . 683Putting Elements Together . . . . . . . . . . . . . 684Speed Control . . . . . . . . . . . . . . . . . . . . . . . 686

Chapter 15 Chemical CompoundsCabbage Patch Indicators . . . . . . . . . . . . . . 688Making Salt . . . . . . . . . . . . . . . . . . . . . . . . . 690

Chapter 16 Atomic EnergyDomino Chain Reactions . . . . . . . . . . . . . . 692

Chapter 17 Introduction to ElectricityStop the Static Electricity! . . . . . . . . . . . . . . 694Potato Power . . . . . . . . . . . . . . . . . . . . . . . . 695Circuitry 101 . . . . . . . . . . . . . . . . . . . . . . . . 696

Chapter 18 ElectromagnetismMagnetic Mystery . . . . . . . . . . . . . . . . . . . . 698Electricity from Magnetism . . . . . . . . . . . . . 699Build a DC Motor . . . . . . . . . . . . . . . . . . . . 700

Chapter 19 Electronic Technology Tune In! . . . . . . . . . . . . . . . . . . . . . . . . . . . 702

Chapter 20 The Energy of WavesWave Energy and Speed . . . . . . . . . . . . . . . 706Wave Speed, Frequency, and Wavelength . . 708

Chapter 21 The Nature of SoundEasy Listening . . . . . . . . . . . . . . . . . . . . . . . 710The Speed of Sound . . . . . . . . . . . . . . . . . . . 712Tuneful Tube . . . . . . . . . . . . . . . . . . . . . . . . 713The Energy of Sound . . . . . . . . . . . . . . . . . . 714

Chapter 22 The Nature of LightWhat Color of Light Is Best

for Green Plants? . . . . . . . . . . . . . . . . . . 716Which Color Is Hottest? . . . . . . . . . . . . . . . 717Mixing Colors . . . . . . . . . . . . . . . . . . . . . . . 718

Chapter 23 Light and Our WorldMirror Images . . . . . . . . . . . . . . . . . . . . . . . 720Images from Convex Lenses . . . . . . . . . . . . 722


Exploring, inventing,and investigating areessential to the studyof science. However,these activities canalso be dangerous.To make sure that

your experimentsand explorations are

safe, you must beaware of a variety of

safety guidelines.

You have probably heard of the saying,“It is better to be safe than sorry.” This is par-ticularly true in a science classroom whereexperiments and explorations are being per-formed. Being uninformed and careless canresult in serious injuries. Don’t take chanceswith your own safety or with anyone else’s.

Following are important guidelines forstaying safe in the science classroom. Yourteacher may also have safety guidelines andtips that are specific to your classroom andlaboratory. Take the time to be safe.

Safety Symbols All of the experiments and investigations inthis book and their related worksheets includeimportant safety symbols to alert you to par-ticular safety concerns. Become familiar withthese symbols so that when you see them,you will know what they mean and what todo. It is important that you read this entiresafety section to learn about specific dangersin the laboratory.

If you are instructed tonote the odor of a sub-stance, wave the fumestoward your nose withyour hand. Never put yournose close to the source.

Eye protection

Clothing protection

Handsafety

Heatingsafety

Electricsafety

Chemicalsafety

Sharpobject

Animalsafety

Plantsafety

LabBook Safety First!622

Safety Rules!Start Out RightAlways get your teacher’s permission beforeattempting any laboratory exploration. Readthe procedures carefully, and pay particularattention to safety information and cautionstatements. If you are unsure about what asafety symbol means, look it up or ask yourteacher. You cannot be too careful when itcomes to safety. If an accident does occur,inform your teacher immediately, regardlessof how minor you think the accident is.

Eye SafetyWear safety goggles when workingaround chemicals, acids, bases, orany type of flame or heating device.Wear safety goggles any time thereis even the slightest chance that harmcould come to your eyes. If any sub-stance gets into your eyes, notify yourteacher immediately, and flush your eyeswith running water for at least 15 minutes.Treat any unknown chemical as if it were adangerous chemical. Never look directly intothe sun. Doing so could cause permanentblindness.

Avoid wearing contact lensesin a laboratory situation. Even

if you are wearing safetygoggles, chemicals canget between the contactlenses and your eyes. Ifyour doctor requiresthat you wear contactlenses instead of glasses,

wear eye-cup safety gog-gles in the lab.

Safety EquipmentKnow the locations of the nearest fire alarmsand any other safety equipment, such as fireblankets and eyewash fountains, as identified by your teacher, and know the procedures for using them.

Be extra careful when using any glassware. When adding a heavy object to a gradu-ated cylinder, tilt the cylinder so the object slides slowly to the bottom.

NeatnessKeep your work area free of all unnecessarybooks and papers. Tie back long hair, andsecure loose sleeves or other loose articles ofclothing, such as ties and bows. Remove dan-gling jewelry. Don’t wear open-toed shoes orsandals in the laboratory. Never eat, drink, orapply cosmetics in a laboratory setting. Food,drink, and cosmetics can easily become con-taminated with dangerous materials.

Certain hair products (such as aerosol hairspray) are flammable and should not be wornwhile working near an open flame. Avoidwearing hair spray or hair gel on lab days.

Sharp/Pointed ObjectsUse knives and other sharp instruments withextreme care. Never cut objects while hold-ing them in your hands. Place objects on a suitable work surface for cutting.

623Safety First! LabBookCopyright © by Holt, Rinehart and Winston. All rights reserved.

Copyright © by Holt, Rinehart and Winston. All rights reserved.624

HeatWear safety goggles when using a heatingdevice or a flame. Whenever possible, use anelectric hot plate as a heat source instead ofan open flame. When heating materials in atest tube, always angle the test tube away fromyourself and others. In order to avoid burns,wear heat-resistant gloves whenever instructedto do so.

ElectricityBe careful with electrical cords. When usinga microscope with a lamp, do not place thecord where it could trip someone. Do not letcords hang over a table edge in a way thatcould cause equipment to fall if the cord isaccidentally pulled. Do not use equipmentwith damaged cords. Be sure your hands aredry and that the electrical equip-ment is in the “off” positionbefore plugging it in. Turn offand unplug electricalequipment when youare finished.

ChemicalsWear safety goggles when handling anypotentially dangerous chemicals, acids, orbases. If a chemical is unknown, handle it asyou would a dangerous chemical. Wear anapron and safety gloves when working withacids or bases or whenever you are told todo so. If a spill gets on your skin or cloth-ing, rinse it off immediately with water forat least 5 minutes while calling to yourteacher.

Never mix chemi-cals unless your teachertells you to do so. Nevertaste, touch, or smellchemicals unless youare specifically directedto do so. Before work-ing with a flammableliquid or gas, check forthe presence of anysource of flame, spark,or heat.

LabBook

625Safety First! LabBook

Animal SafetyAlways obtain your teacher’s permissionbefore bringing any animal into the schoolbuilding. Handle animals only as your teacherdirects. Always treat animals carefully andwith respect. Wash your hands thoroughlyafter handling any animal.

Plant SafetyDo not eat any part of a plant or plant seedused in the laboratory. Wash hands thor-oughly after handling any part of a plant.When in nature, do not pick any wild plantsunless your teacher instructs you to do so.

GlasswareExamine all glasswarebefore use. Be sure thatglassware is clean and free of chips and cracks.Report damaged glassware to your teacher.Glass containers used for heating should bemade of heat-resistant glass.


Materials• a sealed mystery box

Exploring the UnseenYour teacher will give you a box in which a special divider hasbeen created. Your task is to describe this divider as precisely aspossible—without opening the box! Your only aid is a marble thatis also inside the box. This task will allow you to demonstrateyour understanding of the scientific method. Good luck!

Chapter 1 LabBook626

DISCOVERY LAB

Ask a Question

1. In your ScienceLog, record the questionthat you are trying to answer by doing thisexperiment. (Hint: Read the introductoryparagraph again if you are not sure whatyour task is.)

Form a Hypothesis

2. Before you begin the experiment, thinkabout what’s required. Do you think youwill be able to easily determine the shapeof the divider? What about its texture? itscolor? In your ScienceLog, write a hypoth-esis that states how much you think you willbe able to determine about the divider dur-ing the experiment. (Remember, you can’topen the box!)

Test the Hypothesis

3. Using all the methods you can think of(except opening the box), test your hypoth-esis. Make careful notes about your testingand observations in your ScienceLog.

Analyze the Results

4. What characteristics of the divider were youable to identify? Draw or write your bestdescription of the interior of the box.

5. Do your observations support your hypoth-esis? Explain. If your results do not supportyour hypothesis, write a new hypothesisand test it.

6. With your teacher’s permission, open thebox and look inside. Record your observa-tions in your ScienceLog.

Communicate Results

7. Write a paragraph summarizing your experi-ment. Be sure to include your methods,whether your results supported yourhypothesis, and how you could improveyour methods.

Using Scientific Methods


Off to the Races!Scientists often use models—representations of objects or systems.Physical models, such as a model airplane, are generally a differ-ent size than the objects they represent. In this lab you will builda model car, test its design, and then try to improve the design.

Procedure

1. Using the materials listed, design and build a car that willcarry the load (the eraser or block of wood) down the rampas quickly as possible. Your car must be no wider than 8 cm,it must have room to carry the load, and it must roll.

2. As you test your design, do not be afraid to rebuild orredesign your car. Improving your methods is an importantpart of scientific progress.

3. When you have a design that works well, measure the timerequired for your car to roll down the ramp. Record this timein your ScienceLog. Repeat this step several times.

4. Try to improve your model. Find one thing that you canchange to make your model car roll faster down the ramp. Inyour ScienceLog, write a description of the change.

5. Repeat step 3.

Analysis

6. Why is it important to have room in the model car for theeraser or wood block? (Hint: Think about the function of areal car.)

7. Before you built the model car, you created a design for it. Do you think this design is also a model? Explain.

8. Based on your observations in this lab, list three reasons why it is helpful for automobile designers to build and test small model cars rather than immediately building a full-size car.

9. In this lab you built a model that wassmaller than the object it represented.Some models are larger than the objectsthey represent. List three examples oflarger models that are used to representobjects. Why is it helpful to use a largermodel in these cases?

Materials• 2 sheets of typing paper

• glue

• 16 cm clothes-hanger wire

• pliers or wire cutters

• metric ruler

• rubber eraser or woodenblock

• ramp (board and text-books)

• stopwatch

MAKING MODELS

Chapter 1 LabBook 627Copyright © by Holt, Rinehart and Winston. All rights reserved.

Measuring Liquid VolumeIn this lab you will use a graduated cylinder to measure and trans-fer precise amounts of liquids. Remember, in order to accuratelymeasure liquids in a graduated cylinder, you should read the levelat the bottom of the meniscus, the curved surface of the liquid.

Procedure

1. Using the masking tape and marker, label the test tubes A, B,C, D, E, and F. Place them in the test-tube rack. Be careful notto confuse the test tubes.

2. Using the 10 mL graduated cylinder and the funnel, pour 14 mLof the red liquid into test tube A. (To do this, first pour 10 mLof the liquid into the test tube and then add 4 mL of liquid.)

3. Rinse the graduated cylinder and funnelbetween uses.

4. Measure 13 mL of the yellow liquid, and pourit into test tube C. Then measure 13 mL ofthe blue liquid, and pour it into test tube E.

5. Transfer 4 mL of liquid from test tube Cinto test tube D. Transfer 7 mL of liquidfrom test tube E into test tube D.

6. Measure 4 mL of blue liquid from thebeaker, and pour it into test tube F.Measure 7 mL of red liquid from thebeaker, and pour it into test tube F.

7. Transfer 8 mL of liquid from test tube Ainto test tube B. Transfer 3 mL of liquidfrom test tube C into test tube B.

Collect Data

8. Make a data table in your ScienceLog, and record the color of the liquid ineach test tube.

9. Use the graduated cylinder to meas-ure the volume of liquid in each testtube, and record the volumes in yourdata table.

10. Record your color observations in a table ofclass data prepared by your teacher. Copythe completed table into your ScienceLog.

Analysis

11. Did all of the groups report the samecolors? Explain why the colors were thesame or different.

12. Why should you not fill the graduatedcylinder to the very top?

Materials• masking tape

• marker

• 6 large test tubes

• test-tube rack

• 10 mL graduated cylinder

• 3 beakers filled with colored liquid

• small funnel

SKILL BUILDER

628 Chapter 1 LabBookCopyright © by Holt, Rinehart and Winston. All rights reserved.

Coin OperatedAll pennies are exactly the same, right? Probably not! After all,each penny was made in a certain year at a specific mint, andeach has traveled a unique path to reach your classroom. But allpennies are similar. In this lab you will investigate differences andsimilarities among a group of pennies.

Procedure

1. Write the numbers 1 through 10 on a page in yourScienceLog, and place a penny next to each number.

2. Use the metric balance to find the mass of each penny to thenearest 0.1 g. Record each measurement in your ScienceLog.

3. On a table that your teacher will provide, make a mark in thecorrect column of the table for each penny you measured.

4. Separate your pennies into piles based on the class data.Place each pile on its own sheet of paper.

5. Measure and record the mass of each pile. Write the mass onthe paper you are using to identify the pile.

6. Fill a graduated cylinder about halfway with water. Carefullymeasure the volume, and record it.

7. Carefully place the pennies from one pile in the graduatedcylinder. Measure and record the new volume.

8. Carefully remove the pennies from the graduated cylinder,and dry them off.

9. Repeat steps 6 through 8 for each pile of pennies.

Analyze the Results

10. Determine the volume of the displaced water by subtracting theinitial volume from the final volume. This amount is equal tothe volume of the pennies. Record the volume of each pile ofpennies.

11. Calculate the density of each pile. To do this, divide the totalmass of the pennies by the volume of the pennies. Record thedensity in your ScienceLog.

Draw Conclusions

12. How is it possible for the pennies to have different densities?

13. What clues might allow you to separate the pennies into the same groups without experimentation? Explain.

Materials• 10 pennies

• metric balance

• few sheets of paper


• water

• paper towels

SKILL BUILDER


Materials

Part A

• graduated cylinder

• water

• various small objects sup-plied by your teacher

Part B

• bottom half of a 2 L plastic bottle or similarcontainer

• water

• aluminum pie pan

• paper towels

• funnel


Volumania!You have learned how to measure the volume of a solid objectthat has square or rectangular sides. But there are lots of objectsin the world that have irregular shapes. In this lab activity, you’lllearn some ways to find the volume of objects that have irregularshapes.

Part A: Finding the Volume of Small Objects

Procedure

1. Fill a graduated cylinder half full with water. Read the volumeof the water, and record it in your ScienceLog. Be sure to lookat the surface of the water at eye level and to read the vol-ume at the bottom of the meniscus, as shown below.

2. Carefully slide one of the objects into the tilted graduatedcylinder, as shown below.

3. Read the new volume, and record it in your ScienceLog.

4. Subtract the old volume from the new volume. The resultingamount is equal to the volume of the solid object.

5. Use the same method to find the volume of the otherobjects. Record your results in your ScienceLog.

Analysis

6. What changes do you have to maketo the volumes you determine inorder to express them correctly?

7. Do the heaviest objects always havethe largest volumes? Why or why not?

630

SKILL BUILDER

Chapter 2 LabBook

Read volume here


631

Part B: Finding the Volume of Your Hand

Procedure

8. Completely fill the container with water. Put thecontainer in the center of the pie pan. Be surenot to spill any of the water into the pie pan.

9. Make a fist, and put your hand into the con-tainer up to your wrist.

10. Remove your hand, and let the excess waterdrip into the container, not the pie pan. Dryyour hand with a paper towel.

11. Use the funnel to pour the overflow water intothe graduated cylinder. Measure the volume.This is the volume of your hand. Record the volume in yourScienceLog. (Remember to use the correct unit of volume fora solid object.)

12. Repeat this procedure with your other hand.

Analysis

13. Was the volume the same for both of your hands? If not,were you surprised? What might account for a person’s handshaving different volumes?

14. Would it have made a difference if you had placed your openhand into the container instead of your fist? Explain your reasoning.

15. Compare the volume of your right hand with the volume ofyour classmates’ right hands. Create a class graph of right-hand volumes. What is the average right-hand volume foryour class?

Going Further Design an experiment to determine the volume of a person’s

body. In your plans, be sure to include the materials neededfor the experiment and the procedures that must befollowed. Include a sketch that shows how your materi-als and methods would be used in this experiment.

Using an encyclopedia, the Internet, or otherreference materials, find out how the volumes ofvery large samples of matter—such as an entireplanet—are determined.

Chapter 2 LabBookCopyright © by Holt, Rinehart and Winston. All rights reserved.

Determining DensityThe density of an object is its mass divided by its volume. Buthow does the density of a small amount of a substance relate tothe density of a larger amount of the same substance? In this lab,you will calculate the density of one marble and of a group ofmarbles. Then you will confirm the relationship between the massand volume of a substance.

Collect Data

1. Copy the table below in your ScienceLog. Include one row for each marble.

2. Fill the graduated cylinder with 50.0 mL ofwater. If you put in too much water, twistone of the paper towels and use its end toabsorb excess water.

3. Measure the mass of a marble as accuratelyas you can (to at least one-tenth of a gram).Record the marble’s mass in the table.

4. Carefully drop the marble in the tiltedcylinder, and measure the total volume.Record the volume in the third column.

5. Measure and record the mass of anothermarble. Add the masses of the marblestogether, and record this value in thesecond column of the table.

6. Carefully drop the second marble in thegraduated cylinder. Complete the row ofinformation in the table.

7. Repeat steps 5 and 6, adding one marble ata time. Stop when you run out of marbles,the water no longer completely covers themarbles, or the graduated cylinder is full.


Analyze the Results

8. Examine the data in your table. As thenumber of marbles increases, what hap-pens to the total mass of the marbles?What happens to the volume of the marbles? What happens to the density of the marbles?

9. Graph the total mass of the marbles (y-axis) versus the volume of the marbles(x-axis). Is the graph a straight line or acurved line?

Draw Conclusions

10. Does the density of a substance depend onthe amount of substance present? Explainhow your results support your answer.

Materials• 100 mL graduated

cylinder

• water

• paper towels

• 8 to 10 glass marbles

• metric balance

• graph paper

SKILL BUILDER

Mass of Total mass of Total Volume of marbles, mL Density of marbles, g/mL marble, g marbles, g volume, (total volume minus (total mass of marbles divided

mL 50.0 mL) by volume of marbles)

Going FurtherCalculate the slope of the graph. How doesthe slope compare with the values in the column titled “Density of marbles”? Explain.


Layering LiquidsYou have learned that liquids form layers according to theirdensities. In this lab, you’ll discover whether it matters in whichorder you add the liquids.

Make a Prediction

1. Does the order in which you add liquids ofdifferent densities to a container affect theorder of the layers formed by those liquids?

Conduct an Experiment

2. Using the graduated cylinders, add 10 mL ofeach liquid to the clear container. Rememberto read the volume at the bottom of themeniscus, as shown below. In yourScienceLog, record the order in which youadded the liquids.

3. Observe the liquids in the container. Inyour ScienceLog, sketch what you see. Besure to label the layers and the colors.

4. Add 10 mL more of liquid C. Observe whathappens, and write your observations inyour ScienceLog.

5. Add 20 mL more of liquid A. Observe whathappens, and write your observations inyour ScienceLog.

Analyze Your Results

6. Which of the liquids has the greatestdensity? Which has the least density? How can you tell?

7. Did the layers change position when you added more of liquid C? Explain youranswer.

8. Did the layers change positionwhen you added more of liquid A? Explain your answer.

Communicate Your Results

9. Find out in what order your classmatesadded the liquids to the container.Compare your results with those of a class-mate who added the liquids in a differentorder. Were your results different? In yourScienceLog, explain why or why not.

Draw Conclusions

10. Based on your results, evaluate yourprediction from step 1.

Materials• liquid A

• liquid B

• liquid C

• beaker or other small,clear container

• 10 mL graduated cylinders (3)

• 3 funnels

DISCOVERY LAB

Chapter 2 LabBook 633



Materials• 4 spatulas

• baking powder

• plastic-foam egg carton

• 3 eyedroppers

• water

• stirring rod

• vinegar

• iodine solution

• baking soda

• cornstarch

• sugar

White Before Your EyesYou have learned how to describe matter based on its physicaland chemical properties. You have also learned some clues thatcan help you determine whether a change in matter is a physicalchange or a chemical change. In this lab, you’ll use what you havelearned to describe four substances based on their properties andthe changes they undergo.

Procedure

1. Copy Table 1 and Table 2, shown on the next page, into yourScienceLog. Be sure to leave plenty of room in each box towrite down your observations.

2. Use a spatula to place a small amount (just enough to coverthe bottom of the cup) of baking powder into three cups ofyour egg carton. Look closely at the baking powder, andrecord observations of its color, texture, etc., in the column ofTable 1 titled “Unmixed.”

3. Use an eyedropper to add 60 drops of water to the bakingpowder in the first cup, as shown below. Stir with the stirringrod. Record your observations in Table 1 in the column titled“Mixed with water.” Clean your stirring rod.

4. Use a clean dropper to add 20 drops of vinegar to the secondcup of baking powder. Stir. Record your observations in thecolumn titled “Mixed with vinegar.” Clean your stirring rod.

634

SKILL BUILDER


635

5. Use a clean dropper to add five drops of iodine solution tothe third cup of baking powder. Stir. Record your observationsin the column in Table 1 titled “Mixed with iodine solution.”Clean your stirring rod.Caution: Be careful when using iodine. Iodine will stain yourskin and clothes.

6. Repeat steps 2–5 for each of the other substances. Use aclean spatula for each substance.

Analysis

7. In Table 2, write the type of change you observed, and statethe property that the change demonstrates.

8. What clues did you use to identify when a chemical changehappened?

Mixed with Substance Unmixed Mixed with water Mixed with vinegar iodine solution

Baking powder

Baking soda

Cornstarch

Sugar

Mixed with water Mixed with vinegar Mixed with iodine solution

Substance Change Property Change Property Change Property

Baking powder

Baking soda

Cornstarch

Sugar

Table 1 Observations

Table 2 Changes and Properties


Full of Hot Air!Why do hot-air balloons float gracefully above Earth, while bal-loons you blow up fall to the ground? The answer has to do withthe density of the air inside the balloon. Density is mass per unitvolume, and volume is affected by changes in temperature. In thisexperiment, you will investigate the relationship between thetemperature of a gas and its volume. Then you will be able todetermine how the temperature of a gas affects its density.

Form a Hypothesis

1. How does an increase or decrease in tem-perature affect the volume of a balloon?Write your hypothesis in your ScienceLog.

Test the Hypothesis

2. Fill an aluminum pan with water about 4 to 5 cm deep. Put the pan on the hot plate,and turn the hot plate on.

3. While the water is heating, fill the otherpan 4 to 5 cm deep with ice water.

4. Blow up a balloon inside the 500 mLbeaker, as shown. The balloon should fillthe beaker but should not extend outsidethe beaker. Tie the balloon at its opening.

5. Place the beaker and balloon in the icewater. Observe what happens. Record yourobservations in your ScienceLog.

6. Remove the balloon and beaker from theice water. Observe the balloon for severalminutes. Record any changes.


7. Put on heat-resistant gloves. When the hotwater begins to boil, put the beaker andballoon in the hot water. Observe the bal-loon for several minutes, and record yourobservations.

8. Turn off the hot plate. When the water hascooled, carefully pour it into a sink.

Analyze the Results

9. Summarize your observations of the balloon.Relate your observations to Charles’s law.

10. Was your hypothesis for step 1 supported?If not, revise your hypothesis.

Draw Conclusions

11. Based on your observations, how is thedensity of a gas affected by an increase ordecrease in temperature?

12. Explain in terms of density and Charles’slaw why heating the air allows a hot-airballoon to float.

Materials• 2 aluminum pans

• water

• metric ruler

• hot plate

• ice water

• balloon

• 250 mL beaker

• heat-resistant gloves

DISCOVERY LAB




Materials• water

• 2 empty aluminum cans


• hot plate

• tongs

• 1 L beaker

Can CrusherCondensation can occur when gas particles come near the surfaceof a liquid. The gas particles slow down because they areattracted to the liquid. This reduction in speed causes the gas par-ticles to condense into a liquid. In this lab, you’ll see that particlesthat have condensed into a liquid don’t take up as much spaceand therefore don’t exert as much pressure as they did in thegaseous state.


1. Place just enough water in an aluminum can to slightly coverthe bottom.

2. Put on heat-resistant gloves. Place the aluminum can on ahot plate turned to the highest temperature setting.

3. Heat the can until the water is boiling. Steam should be risingvigorously from the top of the can.

4. Using tongs, quickly pick up thecan and place the top 2 cm of the can upside down in the 1 L beaker filled with room-temperature water.

5. Describe your observations in yourScienceLog.

Analyze the Results

6. The can was crushed because theatmospheric pressure outside thecan became greater than the pres-sure inside the can. Explain whathappened inside the can to causethis.

Draw Conclusions

7. Inside every popcorn kernel is asmall amount of water. When youmake popcorn, the water insidethe kernels is heated until itbecomes steam. Explain how thepopping of the kernels is theopposite of what you saw in thislab. Be sure to address the effectsof pressure in your explanation.

SKILL BUILDER

Going FurtherTry the experiment again, but use ice water insteadof room-temperature water. Explain your results interms of the effects of temperature.


Materials

Part A

• 250 or 400 mL beaker

• water


• hot plate

• thermometer

• stopwatch

• graph paper

Part B


• water

• large coffee can

• crushed ice

• rock salt

• thermometer

• wire-loop stirring device

• stopwatch

• graph paper

A Hot and Cool LabWhen you add energy to a substance through heating, does thesubstance’s temperature always go up? When you remove energyfrom a substance through cooling, does the substance’s tempera-ture always go down? In this lab you’ll investigate these importantquestions with a very common substance—water.

Part A: Boiling Water

Make a Prediction

1. What happens to the temperature of boiling water when you continue to add energy through heating?

Procedure

2. Fill the beaker about one-third to one-half full with water.

3. Put on heat-resistant gloves. Turn on the hot plate, and putthe beaker on the burner. Put the thermometer in the beaker.Caution: Be careful not to touch the burner.

Collect Data

4. In a table like the one below, record the temperature of thewater every 30 seconds. Continue doing this until about one-fourth of the water boils away. Note the first temperaturereading at which the water is steadily boiling.

5. Turn off the hot plate.

6. While the beaker is cooling, make agraph of temperature (y-axis) versustime (x-axis). Draw an arrow pointing tothe first temperature at which the waterwas steadily boiling.

7. After you finish the graph, use heat-resistant gloves to pick up the beaker.Pour the warm water out, and rinse thewarm beaker with cool water. Caution: Even after cooling, the beakeris still too warm to handle withoutgloves.


Time (s) 30 60 90 120 150 180 210 etc.

Temperature (C)

DISCOVERY LAB


Part B: Freezing Water

Make Another Prediction

8. What happens to the temperature of freezing water when youcontinue to remove energy through cooling?

Procedure

9. Put approximately 20 mL of water in the graduated cylinder.

10. Put the graduated cylinder in the coffee can, and fill in aroundthe graduated cylinder with crushed ice. Pour rock salt on theice around the graduated cylinder. Place the thermometer andthe wire-loop stirring device in the graduated cylinder.

11. As the ice melts and mixes with the rock salt, the level of icewill decrease. Add ice and rock salt to the can as needed.

Collect Data

12. In a new table, record the temperature of the water in thegraduated cylinder every 30 seconds. Stir the water with thestirring device. Caution: Do not stir with the thermometer.

13. Once the water begins to freeze, stop stirring. Do not try topull the thermometer out of the solid ice in the cylinder.

14. Note the temperature when you first notice ice crystals form-ing in the water. Continue taking readings until the water inthe graduated cylinder is completely frozen.

15. Make a graph of temperature (y-axis) versus time (x-axis).Draw an arrow to the temperature reading at which the firstice crystals form in the water in the graduated cylinder.

Analyze the Results (Parts A and B)

16. What does the slope of each graph represent?

17. How does the slope when the water is boiling compare withthe slope before the water starts to boil? Why is the slopedifferent for the two periods?

18. How does the slope when the water is freezing com-pare with the slope before the water starts to freeze?Why is the slope different for the two periods?

Draw Conclusions (Parts A and B)

19. Addition or subtraction of energy leads to changes in themovement of particles that make up solids, liquids, andgases. Use this idea to explain why the temperature graphs of the two experiments look the way they do.


Materials• 4 small test tubes

• test-tube rack

• masking tape

• 4 chloride test solutions

• spark igniter

• Bunsen burner

• wire and holder

• dilute hydrochloric acid ina small beaker

• distilled water in a smallbeaker

Flame TestsFireworks produce fantastic combinations of color when they areignited. The different colors are the results of burning differentcompounds. Imagine that you are the lead chemist for a fireworkscompany. The label has fallen off one box filled with a compound,and you must identify the unknown compound so that it may beused in the correct fireworks display. To identify the compound,you will use your knowledge that every compound has a uniqueset of properties.

Make a Prediction

1. Can you identify the unknown compound by heating it in a flame? Explain.

Conduct an ExperimentCaution: Be very careful in handling all chemicals. Tell yourteacher immediately if you spill a chemical.

2. Arrange the test tubes in the test-tube rack. Use masking tapeto label the tubes with the following names: calcium chloride,potassium chloride, sodium chloride, and unknown.

3. Copy the table below into your ScienceLog. Then ask yourteacher for your portions of the solutions.


DISCOVERY LAB

Compound

Calcium chloride

Potassium chloride

Sodium chloride

Unknown

Color of flame

Test Results



4. Light the burner. Clean the wire by dipping it into the dilutehydrochloric acid and then into distilled water. Holding thewooden handle, heat the wire in the blue flame of the burneruntil the wire is glowing and it no longer colors the flame.Caution: Use extreme care around an open flame.

Collect Data

5. Dip the clean wire into the first test solution. Hold the wire atthe tip of the inner cone of the burner flame. In the table,record the color given to the flame.

6. Clean the wire by repeating step 4.

7. Repeat steps 5 and 6 for the other solutions.

8. Follow your teacher’s instructions for cleanup and disposal.

Analyze the Results

9. Is the flame color a test for the metal or for the chloride ineach compound? Explain your answer.

10. What is the identity of your unknown solution? How do youknow?

Draw Conclusions

11. Why is it necessary to carefully clean the wire before testingeach solution?

12. Would you expect the compound sodiumfluoride to produce the same color assodium chloride in a flame test? Why orwhy not?

13. Each of the compounds you tested is madefrom chlorine, which is a poisonous gas atroom temperature. Why is it safe to usethese compounds without a gas mask?


A Sugar Cube Race!If you drop a sugar cube into a glass of water, how long will ittake to dissolve? Will it take 5 minutes, 10 minutes, or longer?What can you do to speed up the rate at which it dissolves?Should you change something about the water, the sugar cube, or the process? In other words, what variable should you change?Before reading further, make a list of variables that could bechanged in this situation. Record your list in your ScienceLog.

Make a Prediction

1. Choose one variable to test. In yourScienceLog, record your choice, and predicthow changing your variable will affect therate of dissolving.


2. Pour 150 mL of water into one of thebeakers. Add one sugar cube, and use thestopwatch to measure how long it takes forthe sugar cube to dissolve. You must not dis-turb the sugar cube in any way! Record thistime in your ScienceLog.

3. Tell your teacher how you wish to test thevariable. Do not proceed without his or herapproval. You may need additionalequipment.

4. Prepare your materials to test the variable youhave picked. When you are ready, start yourprocedure for speeding up the dissolving of


the sugar cube. Use the stopwatch to meas-ure the time. Record this time in yourScienceLog.

Analyze the Results

5. Compare your results with the resultsobtained in step 2. Was your predictioncorrect? Why or why not?

Draw Conclusions

6. Why was it necessary to observe the sugarcube dissolving on its own before youtested the variable?

7. Do you think that changing more than onevariable would speed up the rate of dissolvingeven more? Explain your reasoning.

Communicate Results

8. Discuss your results with a group that testeda different variable. Which variable had agreater effect on the rate of dissolving?

Materials• water


• 2 sugar cubes

• 2 beakers or other clearcontainers

• clock or stopwatch

• other materials approvedby your teacher

DISCOVERY LAB



643

Materials• marble

• small, clear container with lid

• heavy cream

• clock or stopwatch

Making ButterA colloid is an interesting substance. It has properties of bothsolutions and suspensions. Colloidal particles are not heavyenough to settle out, so they remain evenly dispersed throughoutthe mixture. In this activity, you will make butter—a very familiarcolloid—and observe the characteristics that classify butter as acolloid.

Procedure

1. Place a marble inside the container, and fill the container withheavy cream. Put the lid tightly on the container.

2. Take turns shaking the container vigorously and constantly for10 minutes. Record the time when you begin shaking in yourScienceLog. Every minute, stop shaking the container andhold it up to the light. Record your observations.

3. Continue shaking the container, taking turns if necessary.When you see, hear, or feel any changes inside the container,note the time and change in your ScienceLog.

4. After 10 minutes of shaking, you should have a lump of “butter” surrounded by liquid inside the container. Describeboth the butter and the liquid in detail in your ScienceLog.

5. Let the container sit for about 10 minutes. Observe thebutter and liquid again, and record your observations inyour ScienceLog.

Analysis

6. When you noticed the change inthe container, what did you thinkwas happening at that point?

7. Based on your observations,explain why butter is classified asa colloid.

8. What kind of mixture is the liquidthat is left behind? Explain.

SKILL BUILDER


Materials• “polluted” water


• 250 mL beakers (4)

• 2 plastic spoons

• small nail

• 8 oz plastic-foam cup (2)

• scissors

• 2 pieces of filter paper

• washed fine sand

• metric ruler

• washed activated charcoal

• rubber band

Unpolluting WaterIn many cities, the water supply comes from a river, lake, or reser-voir. This water may include several mixtures, including suspen-sions (with suspended dirt, oil, or living organisms) and solutions(with dissolved chemicals). To make the water safe to drink, yourcity’s water supplier must remove impurities. In this lab, you willmodel the procedures used in real water-treatment plants.

Part A: Untreated Water

Procedure

1. Measure 100 mL of “polluted” water into a graduated cylin-der. Be sure to shake the bottle of water before you pour soyour sample will include all the impurities.

2. Pour the contents of the graduated cylinder into one of thebeakers.

3. Copy the table below into your ScienceLog, and record yourobservations of the water in the “Before treatment” row.

Part B: Settling InIf a suspension is left standing, the suspended particles will settle to the top or bottom. You should see a layer of oil at the top.

Procedure

4. Separate the oil by carefully pouring the oil into anotherbeaker. You can use a plastic spoon to get the last bit of oil from the water. Record your observations.


Color Clearness Odor Any layers? Any solids? Water volume

Beforetreatment

After oilseparation

After sandfiltration

Aftercharcoal

Observations

MAKING MODELS



Part C: FiltrationCloudy water can be a sign of small particles still in suspension.These particles can usually be removed by filtering. Water-treatment plants use sand and gravel as filters.

Procedure

5. Make a filter as follows:a. Use the nail to poke 5 to 10 small holes in

the bottom of one of the cups.b. Cut a circle of filter paper to fit inside the

bottom of the cup. (This will keep the sandin the cup.)

c. Fill the cup to 2 cm below the rim with wetsand. Pack the sand tightly.

d. Set the cup inside an empty beaker.

6. Pour the polluted water on top of the sand,and let it filter through. Do not pour any ofthe settled mud onto the sand. (Dispose ofthe mud as instructed by your teacher.) Inyour table, record your observations of thewater collected in the beaker.

Part D: Separating SolutionsSomething that has been dissolved in a solvent cannot beseparated using filters. Water-treatment plants use activated charcoal to absorb many dissolved chemicals.

Procedure

7. Place activated charcoal about 3 cm deep in the unused cup.Pour the water collected from the sand filtration into the cup,and stir for a minute with a spoon.

8. Place a piece of filter paper over the top of the cup, and fas-ten it in place with a rubber band. With the paper securely inplace, pour the water through the filter paper and back into aclean beaker. Record your observations in your table.

Analysis (Parts A–D)

9. Is your unpolluted water safe to drink? Why or why not?

10. When you treat a sample of water, do you get out exactly thesame amount of water that you put in? Explain your answer.

11. Some groups may still have cloudy water when they finish.Explain a possible cause for this.


Materials• toy vehicle

• meterstick

• masking tape

• stopwatch

Built for SpeedImagine that you are an engineer at GoCarCo, a toy-vehiclecompany. GoCarCo is trying to beat the competition by building anew toy vehicle. Several new designs are being tested. Your bosshas given you one of the new toy vehicles and instructed you tomeasure its speed as accurately as possible with the tools youhave. Other engineers (your classmates) are testing the otherdesigns. Your results could decide the fate of the company!

Procedure

1. How will you accomplish your goal? Write a paragraph in yourScienceLog to describe your goal and your procedure for thisexperiment. Be sure that your procedure includes several trials.

2. Show your plan to your boss (teacher). Get his or herapproval to carry out your procedure.

3. Perform your stated procedure. Record all data in yourScienceLog. Be sure to express all data in the correct units.

Analysis

4. What was the average speed of your vehicle? How does yourresult compare with the results of the other engineers?

5. Compare your technique for determining the speed of yourvehicle with the techniques of the other engineers. Whichtechnique do you think is the most effective?

6. Was your toy vehicle the fastest? Explain why or why not.


DESIGNYOUR OWN

Going FurtherThink of several conditions that could affect your vehicle’sspeed. Design an experiment to test your vehicle under one ofthose conditions. Write a paragraph in your ScienceLog toexplain your procedure. Be sure to include an explanation ofhow that condition changes your vehicle’s speed.


Materials• scissors

• string

• 1 L container with water-tight lid

• pushpin

• small cork or plastic-foamball

• modeling clay

• water

Detecting AccelerationHave you ever noticed that you can “feel” acceleration? In a car orin an elevator you notice the change in speed or direction—evenwith your eyes closed! Inside your ears are tiny hair cells. Thesecells can detect the movement of fluid in your inner ear. Whenyou accelerate, the fluid does, too. The hair cells detect this accel-eration in the fluid and send a message to your brain. This allowsyou to sense acceleration.

In this activity you will build a device that detects acceleration.Even though this device is made with simple materials, it is verysensitive. It registers acceleration only briefly. You will have to bevery observant when using this device.

Procedure

1. Cut a piece of string that is just long enough to reach threequarters of the way inside the container.

2. Use a pushpin to attach one end of the string to the cork orplastic-foam ball.

3. Use modeling clay to attach the other end of the string to the center of the inside of the container lid. Be careful not to use too much string—the cork(or ball) should hang no farther than three-quarters of the way into the container.

4. Fill the container to the top with water.

5. Put the lid tightly on the container with thestring and cork (or ball) on the inside.

6. Turn the container upside down (lid on thebottom). The cork should float about three-quarters of the way up inside the container,as shown at right. You are now ready to use your accelerometer to detect accelerationby following the steps on the next page.

SKILL BUILDER


7. Put the accelerometer lid side down on atabletop. Notice that the cork floats straightup in the water.

8. Now gently start pushing the accelerometeracross the table at a constant speed. Noticethat the cork quickly moves in the directionyou are pushing then swings backward. Ifyou did not see this happen, try the samething again until you are sure you can seethe first movement of the cork.

648 Chapter 5 LabBook

9. Once you are familiar with how to use youraccelerometer, try the following changes inmotion, and record your observations ofthe cork’s first motion for each change inyour ScienceLog.

a. While moving the device across the table,push a little faster.

b. While moving the device across the table,slow down.

c. While moving the device across the table,change the direction that you are push-ing. (Try changing both to the left and tothe right.)

d. Make any other changes in motion youcan think of. You should only change onepart of the motion at a time.



Analysis

10. The cork moves forward (in the direction you were pushingthe bottle) when you speed up but backward when you slowdown. Why? (Hint: Think about the direction of acceleration.)

11. When you push the bottle at a constant speed, why does thecork quickly swing back after it shows you the direction ofacceleration?

12. Imagine you are standing on a corner,watching a car that is waiting ata stoplight. A passenger insidethe car is holding somehelium balloons. Based onwhat you observed with your accelerometer, whatdo you think willhappen to theballoons whenthe car beginsmoving?

Going FurtherIf you move the bottle in a circle at aconstant speed, what do you predictthe cork will do? Try it, and checkyour answer.


Materials• scissors

• string

• textbook (covered)

• spring scale (force meter)

• 3 to 4 wooden or metalrods

Science FrictionIn this experiment, you will investigate three types of friction—static, sliding, and rolling—to determine which is the largest forceand which is the smallest force.

DISCOVERY LAB

Form a Hypothesis

2. In your ScienceLog, write a statement orstatements that answer the questionsabove. Explain your reasoning.

Test the Hypothesis/Collect Data

3. Cut a piece of string, and tie it in a loopthat fits in the textbook, as shown below.Hook the string to the spring scale.

4. Practice the next three steps several timesbefore you collect data.

5. To measure the static friction between thebook and the table, pull the spring scalevery slowly. Record the largest force on thescale before the book starts to move.

6. After the book begins to move, you candetermine the sliding friction. Record theforce required to keep the book slidingat a slow, constant speed.

7. Place two or three rods under thebook to act as rollers. Make sure therollers are evenly spaced. Placeanother roller in front of thebook so that the book will roll onto it. Pull the forcemeter slowly. Measure theforce needed to keep the bookrolling at a constant speed.

Ask a Question

1. Which type of friction is the largest force—static,sliding, or rolling? Which is the smallest?



Analyze the Results

8. Which type of friction was the largest?Which was the smallest?

9. Do the results support your hypothesis? Ifnot, how would you revise or retest yourhypothesis?

Communicate Results

10. Compare your results with those of anothergroup. Are there any differences? Workingtogether, design a way to improve theexperiment and resolve possible differences.


Chapter 5 LabBook

Materials• metric balance

• small classroom objects

• spring scale (force meter)

• string

• scissors

• graph paper

Relating Mass and WeightWhy do objects with more mass weigh more than objects withless mass? All objects have weight on Earth because their mass isaffected by Earth’s gravitational force. Because the mass of anobject on Earth is constant, the relationship between the mass ofan object and its weight is also constant. You will measure themass and weight of several objects to verify the relationshipbetween mass and weight on the surface of Earth.

Collect Data

1. Copy the table below into your ScienceLog.

2. Using the metric balance, find the mass of five or six smallclassroom objects designated by your teacher. Record themasses in your ScienceLog.

3. Using the spring scale, find the weight of eachobject. Record the weights in your ScienceLog.(You may need to use the string to create a hookwith which to hang some objects from the springscale, as shown at right.)

Analyze the Results

4. Using your data, construct a graph of weight(y-axis) versus mass (x-axis). Draw a linethat best fits all your data points.

5. Does the graph confirm the relationshipbetween mass and weight on Earth?Explain your answer.

Object Mass (g) Weight (N)

Mass and Weight Measurements

SKILL BUILDER


A Marshmallow CatapultCatapults use projectile motion to launch objects across distances.A variety of factors can affect the distance an object can belaunched, such as the weight of the object, how far the catapult ispulled back, and the catapult’s strength. In this lab, you will builda simple catapult and determine the angle at which the catapultwill launch an object the farthest.

Form a Hypothesis

1. At what angle, from 10 to 90, will a catapult launch a marshmallow the farthest?

Test the Hypothesis

2. Copy the table below into your ScienceLog.In your table, add one row each for 20,30, 40, 50, 60, 70, 80, and 90 angles.

3. Attach the plastic spoon to the 1 cm sideof the block with duct tape. Use enoughtape so that the spoon is attached securely.

4. Place one marshmallow in the center ofthe spoon, and tape it to the spoon. Thisserves as a ledge to hold the marshmallowthat will be launched.

5. Line up the bottom corner of the blockwith the bottom center of the protractor, asshown in the photograph. Start with theblock at 10.

6. Place a marshmallow in the spoon, on topof the taped marshmallow. Pull back lightly,and let go. Measure and record the dis-tance from the catapult that the marsh-mallow lands. Repeat the measurement,and calculate an average.

7. Repeat step 6 for each angle up to 90.


Analyze the Results

8. At what angle did the catapult launch the marshmallow the farthest? Comparethis with your hypothesis. Explain any differences.

Draw Conclusions

9. Does the path of an object’s projectilemotion depend on the catapult’s angle?Support your answer with your data.

10. At what angle should you throw a ball or shoot an arrow so that it will fly the farthest? Why? Support your answer withyour data.

Materials• plastic spoon

• block of wood,3.5 cm 3.5 cm 1 cm

• duct tape

• miniature marshmallows

• protractor

• meterstick

Angle

10

Distance 1(cm)

Distance 2(cm)

Averagedistance

(cm)

DISCOVERY LAB




Materials• tape

• 3 m fishing line

• pencil

• small paper cup

• 15 cm pieces of string (2)

• long, thin balloon

• twist tie

• drinking straw

• meterstick

• pennies

Blast Off!You have been hired as a rocket scientist for NASA. Your job is todesign a rocket that will have a controlled flight while carrying apayload. Keep in mind that Newton's laws will have a powerfulinfluence on your rocket.

Procedure

1. When you begin your experiment, your teacher will tape oneend of the fishing line to the ceiling.

2. Use a pencil to poke a small hole in each side of the cupnear the top. Place a 15 cm piece of string through each hole,and tape down the ends inside.

3. Inflate the balloon, and use the twist tie to hold it closed.

4. Tape the free ends of the strings to the sides of the balloonnear the bottom. The cup should hang below the balloon.Your model rocket should look like a hot-air balloon.

5. Thread the fishing line that is hanging from the ceilingthrough the straw. Tape the balloon securely to the straw.

6. Tape the loose end of the fishing line to the floor.

Collect Data

7. Untie the twist tie while holding the end of the balloonclosed. When you are ready, release the end of the balloon.Mark and record the maximum height of the rocket.

8. Repeat the procedure, adding a penny to the cup each timeuntil your rocket cannot lift any more pennies.

Analysis

9. In a paragraph, describe how all three of Newton’s laws influ-enced the flight of your rocket.

10. Draw a diagram of your rocket. Label the action and reactionforces.

MAKING MODELS

Going FurtherBrainstorm ways to modify your rocket so that it will carry themost pennies to the maximum height. Select the best design.When your teacher has approved all the designs, each team willbuild and launch their rocket. Which variable did you modify?How did this variable affect your rocket’s flight?


Materials

Station 1

• hard-boiled egg

• raw egg

Station 2

• coin

• index card

• cup

Station 3

• spool of thread

• suspended mass

• scissors

• meterstick

Inertia-Rama!Inertia is a property of all matter, from small particles of dust toenormous planets and stars. In this lab, you will investigate theinertia of various shapes and types of matter. Keep in mind thateach investigation requires you to either overcome or use theobject’s inertia.

Station 1: Magic Eggs

Procedure

1. There are two eggs at this station—one is hard-boiled (solidall the way through) and the other is raw (liquid inside). Themasses of the two eggs are about the same. The eggs aremarked so that you can tell them apart.

2. You will spin each egg and then stop it from spinning byplacing a finger on its center. Before you do anything toeither egg, write some predictions in your ScienceLog: Whichegg will be the easiest to spin? Which egg will be the easiestto stop?

3. Spin the hard-boiled egg. Then place your finger on it tomake it stop spinning. Record your observations in yourScienceLog.

4. Repeat step 3 with the raw egg.

5. Compare your predictions with your observations. (Repeatsteps 3 and 4 if necessary.)

Analysis

6. Explain why the eggs behave differently when you spin themeven though they should have the same inertia. (Hint: Thinkabout what happens to the liquid inside the raw egg.)

7. In terms of inertia, explain why the eggs react differ-ently when you try to stop them.

Station 2: Coin in a Cup

Procedure

8. At this station, you will find a coin, an index card, anda cup. Place the card over the cup. Then place thecoin on the card over the center of the cup, as shownat right.


SKILL BUILDER



9. In your ScienceLog, write down a method for getting the coininto the cup without touching the coin and without lifting thecard.

10. Try your method. If it doesn’t work, try again until you find amethod that does work. When you are done, place the cardand coin on the table for the next group.

Analysis

11. Use Newton’s first law of motion to explain why the coin fallsinto the cup when your method is used.

12. Explain why pulling on the card slowly will not work, eventhough the coin has inertia. (Hint: Friction is a force.)

Station 3: The Magic Thread

Procedure

13. At this station, you will find a spool of thread and a masshanging from a strong string. Cut a piece of thread about 40 cm long. Tie the thread around the bottom of the mass, as shown at right.

14. Pull gently on the end of the thread. Observe what happens,and record your observations in your ScienceLog.

15. Stop the mass from moving. Now hold the end of the threadso that there is a lot of slack between your fingers and themass.

16. Give the thread a quick, hard pull. You should observe a verydifferent event. Record your observations in your ScienceLog.Throw away the thread.

Analysis

17. Use Newton’s first law of motion to explain why the results ofa gentle pull are so different from the results of a hard pull.

Draw Conclusions

18. Remember that both moving and nonmoving objects haveinertia. Explain why it is hard to throw a bowling ball andwhy it is hard to catch a thrown bowling ball.

19. Why is it harder to run with a backpack full of books thanwith an empty backpack?


Materials• glue

• 10 cm 15 cm rectanglesof cardboard (3)

• 3 pushpins

• string

• rubber band

• 6 plastic straws

• marble

• scissors

• meterstick

Quite a ReactionCatapults have been used for centuries to throw objects great dis-tances. You may already be familiar with catapults after doing themarshmallow catapult lab. According to Newton’s third law ofmotion (whenever one object exerts a force on a second object,the second object exerts an equal and opposite force on the first),when an object is launched, something must also happen to thecatapult. In this activity, you will build a kind of catapult that willallow you to observe the effects of Newton’s third law of motionand the law of conservation of momentum.


1. Glue the cardboard rectangles together to make a stack ofthree.

2. Push two of the pushpins into the cardboard stack near thecorners at one end, as shown below. These will be theanchors for the rubber band.

3. Make a small loop of string.

4. Put the rubber band through the loop of string, and thenplace the rubber band over the two pushpin anchors. Therubber band should be stretched between the two anchorswith the string loop in the middle.

5. Pull the string loop toward the end of the cardboard stackopposite the end with the anchors, and fasten the loop inplace with the third pushpin.

6. Place the six straws about 1 cm apart on a tabletop or on thefloor. Then carefully center the catapult on top of the straws.

7. Put the marble in the closed end of the V formed by the rubber band.


SKILL BUILDER


8. Use scissors to cut the string holding therubber band, and observe what happens.(Be careful not to let the scissors touch thecardboard catapult when you cut the string.)

9. Reset the catapult with a new piece ofstring. Try launching the marble severaltimes to be sure that you have observedeverything that happens during a launch.Record all your observations in yourScienceLog.

Analyze the Results

10. Which has more mass, the marble or thecatapult?

11. What happened to the catapult when themarble was launched?

12. How far did the marble fly before it landed?

13. Did the catapult move as far as the marbledid?

Draw Conclusions

14. Explain why the catapult moved backward.

15. If the forces that made the marble andthe catapult move apart are equal, whydidn’t the marble andthe catapult moveapart the samedistance? (Hint:The fact that themarble can rollafter it lands isnot the answer.)


16. The momentum of an object depends onthe mass and velocity of the object. What is the momentum of the marble before it is launched? What is the momentum of the catapult? Explain your answers.

17. Using the law of conservation of momen-tum, explain why the marble and the cata-pult move in opposite directions after thelaunch.

Going FurtherHow would you modify thecatapult if you wanted tokeep it from moving back-ward as far as it did? (It stillhas to rest on the straws.)Using items that you canfind in the classroom,design a catapult that willmove backward less thanthe original design.


Materials• large rectangular tank or

plastic tub

• water

• metric ruler

• small rectangular baking pan

• labeled masses

• metric balance

• paper towels

Fluids, Force, andFloatingWhy do some objects sink in fluids but others float? In this lab,you’ll get a sinking feeling as you determine that an object floatswhen its weight is less than the buoyant force exerted by the sur-rounding fluid.

Procedure


2. Fill the tank or tub half full with water.

3. Measure (in centimeters) the length, width, and initial heightof the water. Record your measurements in the table.

4. Using the equation given in the table, determine the initialvolume of water in the tank. Record your results in the table.

5. Place the pan in the water, and place masses in the pan, asshown on the next page. Keep adding masses until the pansinks to about three-quarters of its height. This will cause thewater level in the tank to rise. Record the new height of thewater in the table. Then use this value to determine andrecord the new volume of water.


SKILL BUILDER

Measurement Trial 1 Trial 2

Length (l), cm

Width (w), cm

Initial height (h1), cm

Initial volume (V1), cm3

V1 l w h1

New height (h2), cm

New volume (V2), cm3

V2 l w h2

Displaced volume (V), cm3

V V2 V1

Mass of displaced water, gm V 1 g/cm3

Weight of displaced water, N(buoyant force)

Weight of pan and masses, N


6. Determine the volume of the water that was displaced by thepan and masses, and record this value in the table. The displacedvolume is equal to the new volume minus the initial volume.

7. Determine the mass of the displaced water by multiplying thedisplaced volume by its density (1 g/cm3). Record the mass inthe table.

8. Divide the mass by 100. The value you get is the weight of thedisplaced water in newtons (N). This is equal to the buoyantforce. Record the weight of the displaced water in the table.

9. Remove the pan and masses, and determine their total mass(in grams) using the balance. Convert the mass to weight (N),as you did in step 8. Record the weight of the masses and panin the table.

10. Place the empty pan back in the tank. Perform a second trial byrepeating steps 5–9. This time add masses until the pan is justabout to sink.

Analysis

11. In your ScienceLog, compare the buoyant force (the weight ofthe displaced water) with the weight of the pan and masses forboth trials.

12. How did the buoyant force differ between the two trials?Explain.

13. Based on your observations, what would happen if youwere to add even more mass to the pan than you didin the second trial? Explain your answer in terms ofthe buoyant force.

14. What would happen if you put the masses in thewater without the pan? What difference does thepan’s shape make?

659Chapter 7 LabBookCopyright © by Holt, Rinehart and Winston. All rights reserved.

Density DiverCrew members of a submarine can control the submarine’s den-sity underwater by allowing water to flow into and out of specialtanks. These changes in density affect the submarine’s position inthe water. In this lab, you’ll control a “density diver” to learn foryourself how the density of an object affects its position in a fluid.

Form a Hypothesis

1. How does the density of an object deter-mine whether the object floats, sinks, ormaintains its position in a fluid? Write yourhypothesis in your ScienceLog.

Test the Hypothesis

2. Completely fill the 2 L plastic bottle withwater.

3. Fill the diver (medicine dropper) approxi-mately halfway with water, and place it inthe bottle. The diver should float with onlypart of the rubber bulb above the surfaceof the water. If the diver floats too high,carefully remove it from the bottle and adda small amount of water to the diver. Placethe diver back in the bottle. If you add toomuch water and the diver sinks, empty outthe bottle and diver and go back to step 2.

4. Put the cap on the bottle tightly so that nowater leaks out.

5. Apply various pressures to the bottle.Carefully watch the water level inside thediver as you squeeze and release the bot-tle. Record what happens in yourScienceLog.

6. Try to make the diver rise, sink, or stop atany level. Record your technique and yourresults.


Analyze the Results

7. How do the changes inside the diver affectits position in the surrounding fluid?

8. What is the relationship between the waterlevel inside the diver and the diver’s den-sity? Explain.

Draw Conclusions

9. What relationship did you observe betweenthe diver’s density and the diver’s positionin the fluid?

10. Explain how your density diver is like asubmarine.

11. Explain how pressure on the bottle isrelated to the diver’s density. Be sure to

include Pascal’s principle inyour explanation.

12. What was the variablein this experiment?What factors werecontrolled?

Materials• 2 L plastic bottle with

screw-on cap

• water

• medicine dropper

DISCOVERY LAB



LabBook 661

Materials• sheet of paper

Taking FlightWhen air moves above and below the wing of an airplane, the airpressure below the wing is higher than the air pressure above thewing. This creates lift. In this activity, you will build a model air-plane to help you identify how wing size and thrust (forward forceprovided by the engine) affect the lift needed for flight.

Procedure

1. Fold the paper in half lengthwise and open it again, as shownat right. Make sure to crease all folds well.

2. Fold the right- and left-hand corners toward the center crease.

3. Fold the entire sheet in half along the center crease.

4. With the plane lying on its side, fold the top front edge downso that it meets the bottom edge, as shown.

5. Fold the top wing down again, bringing the top edge to thebottom edge.

6. Turn the plane over, and repeat steps 4 and 5.

7. Raise both wings away from the body to a position slightlyabove horizontal. Your plane is ready!

Collect Data

8. Point the plane slightly upward, and gently throw it. Repeatseveral times. Describe your observations in your ScienceLog.Caution: Be sure to point the plane away from people.

9. Make the wings smaller by folding them one more time.Gently throw the plane overhand. Repeat several times.Describe your observations in your ScienceLog.

10. Try to achieve the same flight path you saw when the plane’swings were bigger. Record your technique.

Analysis

11. What happened to the plane’s flight when you reduced thesize of its wings? Explain.

12. What provided your airplane’s thrust?

13. From your observations, how doeschanging the thrust affect the lift?

MAKING MODELS

1

2

3

4

6

5


Materials• flight of stairs

• metric ruler

• stopwatch

A Powerful WorkoutDoes the amount of work you do depend on how fast you do it?No! But doing work in a shorter amount of time does affect yourpower—the rate at which work is done. In this lab, you’ll calculateyour work and power when climbing a flight of stairs at differentspeeds. Then you’ll compare your power with that of an ordinaryhousehold object—a 100 W light bulb.

Ask a Question

1. How does your power when climbing a flight of stairs com-pare with the power of a 100 W light bulb?

Form a Hypothesis

2. In your ScienceLog, write a hypothesis that answers the ques-tion in step 1. Explain your reasoning.

3. Copy Table 1 into your ScienceLog.

Test the Hypothesis

4. Measure the height of one stair step. Record the measure-ment in Table 1.

5. Count the number of stairs, including the top step, and recordthis number in Table 1.

6. Calculate the height (in meters) of the stairs by multiplying thenumber of steps by the height of one step. Record your answer.(You will need to convert from centimeters to meters.)

7. Using a stopwatch, measure how many seconds it takes you towalk slowly up the flight of stairs. Record your measurement inTable 1.

8. Now measure how many seconds it takes you to walk quicklyup the flight of stairs. Be careful not to overexert yourself.


DISCOVERY LAB

Height of Number of Height of Time for slow Time for quickstep (cm) steps stairs (m) walk (s) walk (s)

Table 1 Data Collection



Analyze the Results


10. Determine your weight in newtons by multiplying your weightin pounds (lb) by 4.45 N/lb. Record it in Table 2.

11. Calculate and record your work done to climb the stairs usingthe following equation:

Work Force distance

Remember that 1 N•m is 1 J. (Hint: Remember that force isexpressed in newtons.)

12. Calculate and record your power for each trial (the slow walkand the quick walk) using the following equation:

Power

Remember that the unit for power is the watt (1 W 1 J/s).

Draw Conclusions

13. In step 11 you calculated your work done in climbing thestairs. Why didn’t you calculate your work for each trial?

14. Look at your hypothesis in step 2. Was your hypothesis supported? Write a statement in your ScienceLog thatdescribes how your power in each trial compares with thepower of a 100 W light bulb.

15. The work done to move one electron in a light bulb is verysmall. Write down two reasons why the power is large. (Hints: How many electrons are in the filament of a lightbulb? Why was more power used in your second trial?)

Communicate Results

16. Write your average power in a class data table. Calculate theaverage power for the class. How many light bulbs would ittake to equal the power of one student?

Worktime


Weight Work Power for slow Power for quick(N) (J) walk (W) walk (W)

Table 2 Work and Power Calculations

Where is work done in a light bulb?

Electrons in the filamentmove back and forth very

quickly. These moving electrons do work by

heating up the filament and making it glow.


Inclined to MoveIn this lab, you will examine a simple machine—an inclined plane.Your task is to compare the work done with and without the inclinedplane and to analyze the effects of friction.

Collect Data

4. Keeping the spring scale parallel to theramp, as shown below, slowly raise thebook. Record the input force (the forceneeded to pull the book up the ramp).

5. Increase the height of the ramp by 10 cm.Repeat step 4. Repeat this step for eachramp height up to 50 cm.

Analyze the Results

6. The real work done includes the workdone to overcome friction. Calculate thereal work at each height by multiplying theramp length (converted to meters) by theinput force. Graph your results, plottingwork (y-axis) versus height (x-axis).

7. The ideal work is the work you would do ifthere were no friction. Calculate the idealwork at each height by multiplying theramp height (m) by the output force. Plotthe data on your graph.

Materials• string

• small book

• spring scale

• meterstick

• wooden board

• blocks

• graph paper

SKILL BUILDER

Force vs. Height

Ramp Output Ramp Inputheight (cm) force (N) length (cm) force (N)

10

20

30

40

50

FPO


2. Tie a piece of string around a book. Attach the spring scale tothe string. Use the spring scale to slowly lift the book to aheight of 50 cm. Record the output force (the force needed tolift the book). The output force is constant throughout the lab.

3. Use the board and blocks to make a ramp 10 cm high at thehighest point. Measure and record the ramp length.

Draw Conclusions

8. Does it require more or less force andwork to raise the book using the ramp?Explain, using your calculations and graphs.

9. What is the relationship between the heightof the inclined plane and the input force?

10. Write a statement that summarizes why the slopes of the two graphs are different.


Building MachinesYou are surrounded by machines. Some are simple machines,such as ramps for wheelchair access to a building. Others arecompound machines, like elevators and escalators, that are madeof two or more simple machines. In this lab, you will design andbuild several simple machines and a compound machine.

Procedure

1. Use the listed materials to build a model of each simplemachine: inclined plane, lever, wheel and axle, pulley, screw,and wedge. Describe and draw each model in yourScienceLog.

2. In your ScienceLog, design a compound machine using thematerials listed. You may design a machine that alreadyexists, or you may invent your own machine—be creative!

3. After your teacher approves your design, build your com-pound machine.

Analysis

665

4. List a possible use for each of your simplemachines.

5. Compare your simple machines with thosecreated by your classmates.

6. How many simple machines are in yourcompound machine? List them.

7. Compare your compound machine withthose created by your classmates.

8. What is a possible use for your compoundmachine? Why did you design it as you did?

9. A compound machine is listed in theMaterials list. What is it?

Materials• bottle caps

• cardboard

• craft sticks

• empty thread spools

• glue

• modeling clay

• paper

• pencils

• rubber bands

• scissors

• shoe boxes

• stones

• straws

• string

• tape

• other materials availablein your classroom that areapproved by your teacher

DESIGNYOUR OWN

Going FurtherDesign a compound machine that has all thesimple machines in it. Explain what the machinewill do and how it will make work easier. Withyour teacher’s approval, build your machine.


Materials• wheel and axle assembly

• meterstick

• large mass

• spring scale

• handles

• 0.5 m string

• 2 C-clamps

Wheeling and DealingA wheel and axle is one type of simple machine. A crank handle,such as that used in pencil sharpeners, ice-cream makers, andwater wells is one kind of wheel and axle. In this lab, you will usea crank handle to find out how a wheel and axle helps you dowork. You will also determine what effect the length of the handlehas on the operation of the machine.

Procedure


2. Measure the radius (in meters) of the large dowel in thewheel and axle assembly. Record this in Table 1 as the axleradius, which remains constant throughout the lab. (Hint:Measure the diameter and divide by two.)

3. Using the spring scale, measure theweight of the large mass. Record this inTable 1 as the output force, whichremains constant throughout the lab.

4. Use two C-clamps to secure the wheeland axle assembly to the table, asshown at right.

Collect Data

5. Measure the length (in meters) of han-dle 1. Record this as a wheel radius inTable 1.

6. Insert the handle into the hole in the axle.Attach one end of the string to the largemass and the other end to the screw inthe axle. The mass should hang downand the handle should turn freely.

7. Turn the handle to lift the mass off thefloor. Hold the spring scale upsidedown, and attach it to the end of thehandle. Measure the force (in new-tons) as the handle pulls up on thespring scale. Record this as the inputforce.


SKILL BUILDER


Handle Axle Output Wheel Inputradius force radius force

(m) (N) (m) (N)

1

2

3

4



11. Calculate the following for each handleusing the equations given. Record youranswers in Table 2.

a. Distance axle rotates = 2 π axle radius

Distance wheel rotates = 2 π wheel radius

(Use 3.14 for the value of π.)

b. Work input = input force wheel distance

Work output = output force axle distance

c. Mechanical efficiency =

100

d. Mechanical advantage =wheel radius

axle radius

work outputwork input

Draw Conclusions

12. What happens to work output and workinput as the handle length increases? Why?

13. What happens to mechanical efficiency asthe handle length increases? Why?

14. What happens to mechanical advantage asthe handle length increases? Why?

15. What will happen to mechanical advantageif the handle length is kept constant andthe axle radius gets larger?

16. What factors were controlled in this experiment? What was the variable?

Table 2 Calculations

Handle Axle Wheel Work Work Mechanical Mechanicaldistance distance input output efficiency advantage

(m) (m) (J) (J) (%)

1

2

3

4

8. Remove the spring scale, and lower the mass to the floor.Remove the handle.

9. Repeat steps 5 through 8 with the other three handles. Record all data in Table 1.

Analyze the Results



Materials• 2 or 3 books

• wooden board

• masking tape

• meterstick

• metric balance

• rolling cart

• stopwatch

Finding EnergyWhen you coast down a big hill on a bike or skateboard, you maynotice that you pick up speed. Because you are moving, you havekinetic energy—the energy of motion. Where does that energycome from? In this lab you will find out!

Form a Hypothesis

1. Where does the kinetic energy come from when you rolldown a hill? Write your hypothesis in your ScienceLog.



3. Make a ramp with the books and board.

4. Use masking tape to make a starting line.Be sure the starting line is far enough fromthe top so the cart can be placed behindthe line.

5. Place a strip of masking tape at the bottomof the ramp to mark the finish line.

6. Determine the height of the ramp by meas-uring the height of the starting line andsubtracting the height of the finish line.Record the height of the ramp in meters inTable 1.

7. Measure the distance in meters between thestarting and the finish lines. Record this dis-tance as the length of the ramp in Table 1.


DISCOVERY LAB

Height of Length of Mass of Weight of Averageramp (m) ramp (m) cart (kg) cart (N) time (s)


Time of trial (s)

1 2 3


8. Use the metric balance to find the mass of the cart in grams. Convert this to kilograms by dividing by 1,000. Record the mass inkilograms in Table 1.

9. Multiply the mass by 10 to get the weightof the cart in newtons. Record the weightin Table 1.

Collect Data

10. Set the cart behind the starting line, andrelease it. Use the stopwatch to time howlong it takes for the cart to reach the finishline. Record the time in Table 1.

11. Repeat step 10 twice more, and average theresults. Record the average time in Table 1.


13. Calculate and record the following quanti-ties for the cart in Table 2 using your dataand the equations below:

a. Average speed leanvgetrhag

oeftriammep

b. Final speed 2 average speed (This equation works because the cartaccelerates smoothly from 0 m/s.)

c. Kinetic energy

(Remember that 1 kg • m2/s/s 1 J,the unit used to express energy.)

d. Gravitational potential energy weight height (Remember that 1 N 1 kg • m/s/s, so 1 N 1 m 1 kg • m2/s/s 1 J.)

mass (final speed)22

Draw Conclusions

14. How does the cart’s gravitational potentialenergy at the top of the ramp comparewith its kinetic energy at the bottom? Doesthis support your hypothesis? Explain youranswer.

15. You probably found that the gravitationalpotential energy of the cart at the top ofthe ramp was close but not exactly equalto the kinetic energy of the cart at thebottom. Explain this finding.

16. While riding your bike, you coast downboth a small hill and a large hill. Compareyour final speed at the bottom of the smallhill with your final speed at the bottom ofthe large hill. Explain your answer.

Average Final speed Kinetic energy Gravitational potential energyspeed (m/s) (m/s) at bottom (J) at top (J)

Table 2 Calculations

Analyze the Results



Energy of a PendulumA pendulum clock is a compound machine that uses stored energyto do work. A spring stores energy, and with each swing of thependulum, some of that stored energy is used to move the handsof the clock. In this lab you will take a close look at the energyconversions that occur as a pendulum swings.

Collect Data

1. Make a pendulum by tying the stringaround the hook of the mass. Use themarker and the meterstick to mark pointson the string that are 50 cm, 70 cm, and90 cm away from the mass.

2. Hold the string at the 50 cm mark. Gentlypull the mass to the side, and release itwithout pushing it. Observe at least 10swings of the pendulum.

3. In your ScienceLog, record your observa-tions. Be sure to note how fast and howhigh the pendulum swings.

4. Repeat steps 2 and 3 while holding thestring at the 70 cm mark and again whileholding the string at the 90 cm mark.

Analyze the Results

5. In your ScienceLog, list similarities and dif-ferences in the motion of the pendulumduring all three trials.

6. At which point (or points) of the swing wasthe pendulum moving the slowest? thefastest?

Draw Conclusions

7. In each trial, at which point (or points) ofthe swing did the pendulum have the greatest potential energy? the smallest potential energy? (Hint: Think about your answers to question 6.)


8. At which point (or points) of the swing didthe pendulum have the greatest kineticenergy? the smallest kinetic energy? Explainyour answers.

9. Describe the relationship between the pen-dulum’s potential energy and its kineticenergy on its way down. Explain.

10. What improvements might reduce theamount of energy used to overcome frictionso that the pendulum would swing for a longer period of time?

Materials• 1 m of string

• 100 g hooked mass

• marker

• meterstick

SKILL BUILDER


Materials• raw egg

• empty half-pint milk carton

• assorted materials provided by your teacher

DESIGNYOUR OWNEggstremely Fragile

All moving objects have kinetic energy. The faster an object ismoving, the more kinetic energy it has. When a falling object hitsthe floor, the law of conservation of energy requires that theenergy be transferred to another object or changed into anotherform of energy.

When an unprotected egg hits the ground from a height of 1 m, most of the kinetic energy of the falling egg is transferred to the pieces of the shell—with messy results. In this lab you willdesign a protection system for an egg.


1. Using the materials provided by your teacher, design a protec-tion system that will prevent the egg from breaking when itis dropped from heights of 1, 2, and 3 m. Keep thefollowing points in mind while developing youregg-protection system:

a. The egg and its protection system must fitinside the closed milk carton. (Note: Themilk carton will not be dropped with the egg.)

b. The protective materials don’t have to be soft.

c. The protective materials can surround the eggor can be attached to the egg at various points.

2. In your ScienceLog, explain why you chose yourmaterials.

3. You will perform the three trials at a time andlocation specified by your teacher. Record yourresults for each trial in your ScienceLog.

Analyze the Results

4. Did your egg survive all three trials? If it didnot, why did your egg-protection systemfail? If your egg did survive, what featuresof your egg-protecting system transferred orabsorbed the energy?

Draw Conclusions

5. How do egg cartons like those you find in agrocery store protect eggs from mishandling?


Materials• rubber band

• 10–12 nails

• metric balance

• 30 cm of string

• 9 oz plastic-foam cups (2)

• hot water


• cold water

• thermometer

• paper towels

Feel the HeatHeat is the transfer of energy between objects at different tem-peratures. Energy moves from objects at higher temperatures toobjects at lower temperatures. If two objects are left in contact fora while, the warmer object will cool down, and the cooler objectwill warm up until they eventually reach the same temperature. Inthis activity, you will combine equal masses of water and iron nailsat different temperatures to determine which has a greater effecton the final temperature.

Make a Prediction

1. When you combine substances at two different temperatures,will the final temperature be closer to the initial temperatureof the warmer substance or of the colder substance, or half-way in between? Write your prediction in your ScienceLog.

Conduct an Experiment/Collect Data


3. Use the rubber band to bundle the nails together. Find andrecord the mass of the bundle. Tie a length of string aroundthe bundle, leaving one end of the string 15 cm long.

4. Put the bundle of nails into one of the cups, letting the stringdangle outside the cup. Fill the cup with enough hot water tocover the nails, and set it aside for at least 5 minutes.

5. Use the graduated cylinder to measure enough cold water toexactly equal the mass of the nails (1 mL of water = 1 g).Record this volume in the table.

6. Measure and record the temperature of the hot water withthe nails and the temperature of the cold water.


DISCOVERY LAB

Trial Mass of Volume of Initial temp. of Initial temp. of Final temp. ofnails (g) water that water and nails water to which water and nails

equals mass (°C) nails will be combined (°C)of nails (mL) transferred (°C)

1

2

Data Collection Table



7. Use the string to transfer the bundle ofnails to the cup of cold water. Use the ther-mometer to monitor the temperature ofthe water-nail mixture. When the tempera-ture stops changing, record this final tem-perature in the table.

8. Empty the cups, and dry the nails.

9. For Trial 2, repeat steps 3 through 8, butswitch the hot and cold water. Record all ofyour measurements.

Analyze the Results

10. In Trial 1, you used equal masses of coldwater and nails. Did the final temperaturesupport your initial prediction? Explain.

11. In Trial 2, you used equal masses of hotwater and nails. Did the final temperaturesupport your initial prediction? Explain.

12. In Trial 1, which material—the water or thenails—changed temperature the most afteryou transferred the nails? What about inTrial 2? Explain your answers.

673

Draw Conclusions

13. The cold water in Trial 1 gained energy.Where did the energy come from?

14. How does the energy gained by the nails inTrial 2 compare with the energy lost by thehot water in Trial 2? Explain.

15. Which material seems to be able to holdenergy better? Explain your answer.

16. Specific heat capacity is a property of mat-ter that indicates how much energy isrequired to change the temperature of 1 kgof a material by 1°C. Which material in thisactivity has a higher specific heat capacity(changes temperature less for the sameamount of energy)?

17. Would it be better to have pots and pansmade from a material with a high specificheat capacity or a low specific heat capac-ity? Explain your answer. (Hint: Do youwant the pan or the food in the pan toabsorb all of the energy from the stove?)

Communicate Results

18. Share your results with your classmates.Discuss how you would change your pre-diction to include your knowledge of specific heat capacity.


Save the Cube!The biggest enemy of an ice cube is the transfer of thermal energy—heat. Energy can be transferred to an ice cube in three ways: con-duction (the transfer of energy through direct contact), convection(the transfer of energy by the movement of a liquid or gas), andradiation (the transfer of energy through matter or space). Your challenge in this activity is to design a way to protect an ice cube as much as possible from all three types of energy transfer.

Procedure

1. Follow these guidelines: Use a plastic bagto hold the ice cube and any water from itsmelting. You may use any of the materialsto protect the ice cube. The ice cube, bag,and protection must all fit inside the milkcarton.

2. Describe your proposed design in yourScienceLog. Explain how your design pro-tects against each type of energy transfer.

3. Find the mass of the empty cup, andrecord it in your ScienceLog. Then find andrecord the mass of an empty plastic bag.

4. Place an ice cube in the bag. Quickly findand record their mass together.

5. Quickly wrap the bag (and the ice cubeinside) in its protection. Remember thatthe package must fit in the milk carton.

6. Place your protected ice cube in the “ther-mal zone” set up by your teacher. After 10 minutes, remove the package from thezone and remove the protective materialfrom the plastic bag and ice cube.

7. Open the bag. Pour any water into the cup.Find and record the mass of the cup andwater together.

8. Find and record the mass of the water bysubtracting the mass of the empty cupfrom the mass of the cup and water.

9. Use the same method to find and recordthe mass of the ice cube.


10. Find the percentage of the ice cube thatmelted using the following equation:

% melted 100

11. Record this percentage in your ScienceLogand on the board.

Analysis

12. Compared with other designs in your class,how well did your design protect againsteach type of energy transfer? How couldyou improve your design?

13. Why is a white plastic-foam cooler so useful for keeping ice frozen?

mass of watermass of ice cube

Materials• small plastic bag

• ice cube

• assorted materials pro-vided by your teacher

• empty half-pint milk carton

• metric balance

• small plastic or paper cup

DESIGNYOUR OWN


LabBook 675

Counting CaloriesEnergy transferred by heat is often expressed in units called calories. In this lab, you will build a model of a device called acalorimeter. Scientists often use calorimeters to measure theamount of energy that can be transferred by a substance. In thisexperiment, you will construct your own calorimeter and test it bymeasuring the energy released by a hot penny.

Procedure


2. Place the lid on the small plastic-foam cup, and insert athermometer through the hole in the top of the lid. (The ther-mometer should not touch the bottom of the cup.) Place thesmall cup inside the large cup to complete the calorimeter.

3. Remove the lid from the small cup, and add 50 mL of room-temperature water to the cup. Measure the water’s temperature,and record the value in the first column (0 seconds) of the table.

4. Using tongs, heat the penny carefully. Add the penny to thewater in the small cup, and replace the lid. Start your stopwatch.

5. Every 15 seconds, measure and record the temperature.Gently swirl the large cup to stir the water, and continuerecording temperatures for 2 minutes (120 seconds).

Analysis

6. What was the total temperature change of the water after 2 minutes?

7. The number of calories absorbed by the wateris the mass of the water (in grams) multipliedby the temperature change (in °C) of thewater. How many calories were absorbedby the water? (Hint: 1 mL of water 1 gof water)

8. In terms of heat, explain where thecalories to change the water tempera-ture came from.

Materials• small plastic-foam cup

with lid

• thermometer

• large plastic-foam cup

• water


• tongs

• heat source

• penny

• stopwatch

MAKING MODELS

Seconds 0 15 30 45 60 75 90 105 120

Water temp. (°C)



Materials• 4 protons (white plastic-

foam balls, 2–3 cm indiameter)

• 6 neutrons (blue plastic-foam balls, 2–3 cm indiameter)

• 20 strong-force connectors(toothpicks)

• periodic table

Made to OrderImagine that you are a new employee at the Elements-4-UCompany, which custom builds elements. Your job is to constructthe atomic nucleus for each element ordered by your clients. Youwere hired for the position because of your knowledge aboutwhat a nucleus is made of and your understanding of how iso-topes of an element differ from each other. Now it’s time to putthat knowledge to work!

Procedure

1. Copy the table below into your ScienceLog. Be sure to leaveroom to expand the table to include more elements.

2. Your first assignment: the nucleus of hydrogen-1. Pick up oneproton (a white plastic-foam ball). Congratulations! You havejust built a hydrogen-1 nucleus, the simplest nucleus possible.

3. Count the number of protons and neutrons in the nucleus,and fill in rows 1 and 2 for this element in the table.

4. Use the information in rows 1 and 2 to determine the atomicnumber and mass number of the element. Record this infor-mation in the table.

5. Draw a picture of your model in your ScienceLog.

6. Hydrogen-2 is an isotope of hydrogen that has one protonand one neutron. Using a strong-force connector, add a neu-tron to your hydrogen-1 nucleus. (Remember that in anucleus, the protons and neutrons are held together by thestrong force, which is represented in this activity by the tooth-picks.) Repeat steps 3–5.


Hydrogen-1 Hydrogen-2 Helium-3 Helium-4 Lithium-7 Beryllium-9 Beryllium-10

No. ofprotons

No. of neutrons

Atomic number

Mass number

MAKING MODELS


7. Helium-3 is an isotope of helium that has two protons andone neutron. Add one proton to your hydrogen-2 nucleus tocreate a helium-3 nucleus. Each particle should be connectedto the other two particles so they make a triangle, not a line.Protons and neutrons always form the smallest arrangementpossible because the strong force pulls them together. Repeatsteps 3–5.

8. For the next part of the lab, you will need to use informationfrom the periodic table of the elements. Look at the illustra-tion at right. It shows the periodic table entry for carbon, oneof the most abundant elements on Earth. For your job, themost important information in the periodic table is the atomicnumber. You can find the atomic number of any element atthe top of its entry on the table. In the example, the atomicnumber of carbon is 6.

9. Use the information in the periodic table to build models of thefollowing isotopes of elements: helium-4, lithium-7, beryllium-9,and beryllium-10. Remember to put the protons and neutronsas close together as possible—each particle should attach to atleast two others. Repeat steps 3–5 for each isotope.

Analyze the Results

10. What is the relationship between the number of protons andthe atomic number?

11. If you know the atomic number and the mass number of anisotope, how could you figure out the number of neutronsin its nucleus?

12. Look up uranium on the periodic table.a. What is the atomic number of uranium?b. How many neutrons does the isotope

uranium-235 have?

Communicate Results

13. Compare your model with the models of other groups. How are they similar? How are they different?

Going FurtherWorking with another group, combine your models. Identify the element (and isotope) you have created.

Atomicnumber

677

6

CCarbon

12.0


Materials• bag of objects

• 20 squares of paper, each 3 3 cm

• metric balance

• metric ruler

• 2 sheets of graph paper

Create a Periodic TableYou probably have classification systems for many things in yourlife, such as your clothes, your books, and your CDs. One of themost important classification systems in science is the periodictable of the elements. In this lab you will develop your own clas-sification system for a collection of ordinary objects. You will ana-lyze trends in your system and compare your system with theperiodic table of the elements.

Procedure

1. Your teacher will give you a bag of objects. Your bag is missingone item. Examine the items carefully. Describe the missingobject in as many ways as you can in your ScienceLog. Be sureto include the reasons why you think the missing object hasthese characteristics.

2. Lay the paper squares out on your desk or table so that youhave a grid of five rows of four squares each.

3. Arrange your objects on the grid in a logical order. (You mustdecide what order is logical!) You should end up with oneblank square for the missing object.

4. In your ScienceLog, describe the basis for your arrangement.

5. Measure the mass (g) and diameter (mm) of each object, andrecord your results in the appropriate square. Each square(except the empty one) should have one object and two writ-ten measurements on it.

MAKING MODELS



6. Examine your pattern again. Does the order in which yourobjects are arranged still make sense? Explain.

7. Rearrange the squares and their objects if necessary toimprove your arrangement. Describe the basis for the newarrangement in your ScienceLog.

8. Working across the rows, number the squares 1 to 20. Whenyou get to the end of a row, continue numbering in the firstsquare of the next row.

9. Copy your grid into your ScienceLog. In each square, be sureto list the type of object and label all measure-ments with appropriate units.

Analyze the Results

10. Make a graph of mass (y-axis) ver-sus object number (x-axis). Labeleach axis, and title the graph.

11. Now make a graph of diameter (y-axis) versus object number (x-axis).

Communicate Results

12. Discuss each graph with your class-mates. Try to identify any important fea-tures of the graph. For example, does thegraph form a line or a curve? Is thereanything unusual about the graph? Whatdo these features tell you? Write youranswers in your ScienceLog.

Draw Conclusions

13. How is your arrangement of objects similar tothe periodic table of the elements found inthis textbook? How is your arrangement different from thatperiodic table?

14. Look back at your prediction about the missing object. Doyou think it is still accurate? Try to improve your descriptionby estimating the mass and diameter of the missing object.Record your estimates in your ScienceLog.

15. Mendeleev created a periodic table of elements and predictedcharacteristics of missing elements. How is your experimentsimilar to Mendeleev’s work?


Materials• marshmallows (2 of one

color, 1 of another color)

• toothpicks

Covalent MarshmallowsA hydrogen atom has one electron in its outer energy level, but twoelectrons are required to fill its outer level. An oxygen atom has sixelectrons in its outer energy level, but eight electrons are requiredto fill its outer level. In order to fill their outer energy levels, twoatoms of hydrogen and one atom of oxygen can share electrons, asshown below. Such a sharing of electrons to fill the outer level ofatoms is called covalent bonding. When hydrogen and oxygen bondin this manner, a molecule of water is formed. In this lab you willbuild a three-dimensional model of water in order to better under-stand the covalent bonds formed in a water molecule.

Procedure

1. Using the marshmallows and toothpicks, create a model of awater molecule. Use the diagram above for guidance inbuilding your model.

2. Draw a sketch of your model in your ScienceLog. Be sure tolabel the hydrogen and oxygen atoms on your sketch.

3. Draw an electron-dot diagram of the water molecule in yourScienceLog. (Refer to the chapter text if you need help draw-ing an electron-dot diagram.)

Analysis

4. What do the marshmallows represent? What do the tooth-picks represent?

5. Why are the marshmallows different colors?

6. Compare your model with the picture above. How might yourmodel be improved to more accurately represent a water molecule?


Oxygen

Hydrogen

Hydrogen

A Model of a Water Molecule

MAKING MODELS



7. Hydrogen in nature can covalently bond to form hydrogenmolecules, H2. How could you model this using the marsh-mallows and toothpicks?

8. Draw an electron-dot diagram of a hydrogen molecule in your ScienceLog.

9. Which do you think would be more difficult to create—amodel of an ionic bond or a model of a covalent bond?Explain your answer.

Going FurtherCreate a model of a carbon dioxide molecule, which consists oftwo oxygen atoms and one carbon atom. The structure is simi-lar to the structure of water, although the three atoms bond ina straight line instead of at angles. The bond between eachoxygen atom and the carbon atom in a carbon dioxide mol-ecule is a “double bond,” so use two connections. Do the dou-ble bonds in carbon dioxide appear stronger or weaker thanthe single bonds in water? Explain your answer.


Finding a BalanceUsually, balancing a chemical equation involves just writing inyour ScienceLog. But in this activity, you will use models to prac-tice balancing chemical equations, as shown below. By followingthe rules, you will soon become an expert equation balancer!

Procedure

1. The rules:a. Reactant-molecule models may be placed

only to the left of the arrow.b. Product-molecule models may be placed

only to the right of the arrow.c. You may use only complete molecule

models.d. At least one of each of the reactant and

product molecules shown in the equationmust be included in the model when youare finished.

2. Select one of the labeled envelopes. Copythe unbalanced equation written on theenvelope into your ScienceLog.

3. Open the envelope, and pull out the mol-ecule models and the arrow. Place thearrow in the center of your work area.

4. Put one model of each molecule that is areactant on the left side of the arrow andone model of each product on the right side.


5. Add one reactant-molecule or product-molecule model at a time until the numberof each of the different-colored squares oneach side of the arrow is the same.Remember to follow the rules.

6. When the equation is balanced, count thenumber of each of the molecule models youused. Write these numbers as coefficients, asshown in the balanced equation above.

7. Select another envelope, and repeat thesteps until you have balanced all of theequations.

Analysis

8. The rules specify that you are only allowedto use complete molecule models. How isthis similar to what occurs in a real chemicalreaction?

9. In chemical reactions, energy is eitherreleased or absorbed. In your ScienceLog,devise a way to improve the model toshow energy being released or absorbed.

Materials• envelopes, each labeled

with an unbalancedequation

MAKING MODELS

Example

H2 + O2 H2O

Balanced Equation

2H2 + O2 2H2O


Cata-what? Catalyst!Catalysts increase the rate of a chemical reaction without beingchanged during the reaction. In this experiment, hydrogen peroxide,H2O2, decomposes into oxygen, O2, and water, H2O. An enzymepresent in liver cells acts as a catalyst for this reaction. You willinvestigate the relationship between the amount of the catalyst andthe rate of the decomposition reaction.

Ask a Question

1. How does the amount of a catalyst affectreaction rate?

Form a Hypothesis

2. In your ScienceLog, write a statement thatanswers the question above. Explain yourreasoning.

Test the Hypothesis

3. Put a small piece of masking tape near thetop of each test tube, and label the tubes 1,2, and 3.

4. Create a hot-water bath by filling the beakerhalf-full with hot water.

5. Using the funnel and graduated cylinder,measure 5 mL of the hydrogen peroxidesolution into each test tube. Place the testtubes in the hot-water bath for 5 minutes.

6. While the test tubes warm up, grind oneliver cube with the mortar and pestle.

7. After 5 minutes, use the tweezers to placethe cube of liver in test tube 1. Place theground liver in test tube 2. Leave test tube3 alone.

Make Observations

8. Observe the reaction rate (the amount ofbubbling) in all three test tubes, and recordyour observations in your ScienceLog.


9. Does liver appear to be a catalyst? Explainyour answer.

10. Which type of liver (whole or ground) produced a faster reaction? Why?

11. What is the purpose of test tube 3?

Draw Conclusions

12. How do your resultssupport or disproveyour hypothesis?

13. Why was a hot-waterbath used? (Hint:Look in your book for a definition ofactivation energy.)

Materials• 10 mL test tubes (3)

• masking tape

• 600 mL beaker

• hot water

• funnel


• hydrogen peroxidesolution

• 2 small liver cubes

• mortar and pestle

• tweezers

DISCOVERY LAB




Materials• metric balance

• evaporating dish

• weighing paper

• copper powder

• ring stand and ring

• wire gauze

• Bunsen burner or portableburner

• spark igniter

• tongs

Putting Elements TogetherA synthesis reaction is a reaction in which two or more sub-stances combine to form a single compound. The resulting com-pound has different chemical and physical properties than thesubstances from which it is composed. In this activity, you willsynthesize, or create, copper(II) oxide from the elements copperand oxygen.

Conduct an Experiment/Collect Data


2. Use the metric balance to measure the mass (to the nearest 0.1 g) of the emptyevaporating dish. Record this mass in thetable.

3. Place a piece of weighing paper on the met-ric balance, and measure approximately 10 gof copper powder. Record the mass (to thenearest 0.1 g) in the table.Caution: Wear protective gloves whenworking with copper powder.

4. Use the weighing paper to place the copper powder in the evaporating dish. Spread the powder over the bottom and up the sides as much as possible. Discard the weighing paper.



Object Mass (g)

Evaporating dish

Copper powder

Copper + evaporating dish after heating

Copper(II) oxide

SKILL BUILDER


685

5. Set up the ring stand and ring. Place the wiregauze on top of the ring. Carefully place theevaporating dish on the wire gauze.

6. Place the Bunsen burner under the ring andwire gauze. Use the spark igniter to light theBunsen burner.Caution: Use extreme care when workingnear an open flame.

7. Heat the evaporating dish for 10 minutes.

8. Turn off the burner, and allow the evaporat-ing dish to cool for 10 minutes. Use tongsto remove the evaporating dish and place iton the balance to determine the mass.Record the mass in the table.

9. Determine the mass of the reaction prod-uct—copper(II) oxide—by subtracting themass of the evaporating dish from the massof the evaporating dish and copper powderafter heating. Record this mass in the table.

Analyze the Results

10. What evidence of a chemical reaction didyou observe after the copper was heated?

11. Explain why a change in mass occurred.

12. How does the change in mass support theidea that this is a synthesis reaction?

Chapter 14 LabBook

Draw Conclusions

13. Why was powdered copper used ratherthan a small piece of copper? (Hint: Howdoes surface area affect the rate of thereaction?)

14. Why was the copper heated? (Hint: Lookin your book for the discussion of activa-tion energy.)

15. The copper bottoms of cooking pots canturn black when used. How is that similarto the results you obtained in this lab?

Going FurtherRust, shown below, is iron(III) oxide—theproduct of a synthesis reaction between ironand oxygen. How does painting a car helpprevent this type of reaction?


Speed ControlThe reaction rate (how fast a chemical reaction happens) is animportant factor to control. Sometimes you want a reaction totake place rapidly, such as when you are removing tarnish from a metal surface. Other times you want a reaction to happen veryslowly, such as when you are depending on a battery as a sourceof electrical energy. In this lab, you will discover how changing thesurface area and concentration of the reactants affects reactionrate. In this lab, you can estimate the rate of reaction by observinghow fast bubbles form.

Part A—Surface Area

Ask a Question

1. How does changing the surface area of a metal affect reaction rate?

Form a Hypothesis


Test the Hypothesis

3. Use three identical strips of aluminum. Put one strip into a test tube. Place the test tube in the test-tube rack.Caution: The strips of metal may havesharp edges.

4. Carefully fold a second strip in half andthen in half again. Use a text book or otherlarge object to flatten the folded strip asmuch as possible. Place the strip in a sec-ond test tube in the test-tube rack.

5. Use scissors to cut a third strip of aluminuminto the smallest possible pieces. Place allof the pieces into a third test tube, andplace the test tube in the test-tube rack.


6. Use a funnel and a graduated cylinder topour 10 mL of acid A into each of the threetest tubes.Caution: Hydrochloric acid is corrosive. If anyacid should spill on you, immediately flushthe area with water and notify your teacher.

Make Observations

7. Observe the rate of bubble formation ineach test tube. Record your observations inyour ScienceLog.

Analyze the Results

8. Which form of aluminum had the greatestsurface area? Which had the smallest?

9. In the three test tubes, the amount of alu-minum and the amount of acid were thesame. Which form of the aluminumseemed to react the fastest? Which formreacted the slowest? Explain your answers.

10. Do your results support the hypothesis youmade in step 2? Explain.

Materials• 30 mL test tubes (6)

• 6 strips of aluminum, approximately 5 1 cmeach

• test-tube rack

• scissors

• 2 funnels

• 10 mL graduated cylinders (2)

• acid A

• acid B

DISCOVERY LAB



Draw Conclusions

11. Would powdered aluminum react faster orslower than the forms of aluminum youused? Explain your answer.

Part B—Concentration

Ask a Question

12. How does changing the concentration ofacid affect the reaction rate?

Form a Hypothesis


Test the Hypothesis

14. Place one of the three remaining aluminumstrips in each of the three clean test tubes.(Note: Do not alter the strips.) Place thetest tubes in the test-tube rack.

15. Using the second funnel and graduatedcylinder, pour 10 mL of water into one ofthe test tubes. Pour 10 mL of acid B intothe second test tube. Pour 10 mL of acid Ainto the third test tube.

Make Observations

16. Observe the rate of bubble formation inthe three test tubes. Record your observa-tions in your ScienceLog.

Analyze the Results

17. In this set of test tubes, the strips of alu-minum were the same, but the concentra-tion of the acid was different. Acid A ismore concentrated than acid B. Was therea difference between the test tube withwater and the test tubes with acid? Whichtest tube formed bubbles the fastest?Explain your answers.

18. Do your resuIts support the hypothesis youmade in step 13? Explain.

Draw Conclusions

19. Explain why spilled hydrochloric acidshould be diluted with water before it iswiped up.



Color with Effect onLiquid indicator pH litmus paper

Control

Cabbage Patch IndicatorsIndicators are weak acids or bases that change color due to thepH of the substance to which they are added. Red cabbage con-tains a natural indicator that turns specific colors at specific pHs.In this lab you will extract the indicator from red cabbage and use it to determine the pH of several liquids.

Procedure

1. Copy the table below into your ScienceLog. Be sure toinclude one line for each sample liquid.


Materials• distilled water

• 250 mL beaker

• red cabbage leaf

• hot plate

• beaker tongs

• masking tape

• test tubes

• test-tube rack

• eyedropper

• sample liquids providedby teacher

• litmus paper

SKILL BUILDER

2. Put on protective gloves.Place 100 mL of distilledwater in the beaker. Tearthe cabbage leaf into smallpieces, and place the piecesin the beaker.

3. Use the hot plate to heatthe cabbage and water toboiling. Continue boilinguntil the water is deep blue.Caution: Use extreme carewhen working near a hotplate.



4. Use tongs to remove the beaker from thehot plate, and turn the hot plate off. Allowthe solution to cool for 5–10 minutes.

5. While the solution is cooling, use maskingtape and a pen to label the test tubes foreach sample liquid. Label one test tube asthe control. Place the tubes in the rack.

6. Use the eyedropper to place a small amount(about 5 mL) of the indicator (cabbagejuice) in the test tube labeled as the control.Pour a small amount (about 5 mL) of eachsample liquid into the appropriate test tube.

7. Using the eyedropper, place several dropsof the indicator into each test tube andswirl gently. Record the color of each liquidin the table. Use the chart below to deter-mine and record the pH for each sample.

8. Litmus paper is an indicator that turns redin an acid and blue in a base. Test eachliquid with a strip of litmus paper, andrecord the results.

Analysis

9. What purpose does the control serve? Whatis the pH of the control?

10. What colors are associated with acids? withbases?

11. Why is red cabbage juice considered agood indicator?

12. Which do you think would be more usefulto help identify an unknown liquid—litmuspaper or red cabbage juice? Why?

Going FurtherUnlike distilled water, rainwater has some car-bon dioxide dissolved in it. Is rainwater acidic,basic, or neutral? To find out, place a smallamount of the cabbage juice indicator (whichis water-based) in a clean test tube. Use astraw to gently blow bubbles in the indicator.Continue blowing bubbles until you see a colorchange. What can you conclude about the pHof your “rainwater?” What is the purpose ofblowing bubbles in the cabbage juice?

pH 21 3 4 5 6 7 8 9 10 11 12 13 14


690

Making SaltA neutralization reaction between an acid and a base produceswater and a salt. In this lab, you will react an acid with a baseand then let the water evaporate. You will then examine what isleft for properties that tell you that it is indeed a salt.

Procedure

1. Put on protective gloves. Carefully measure 25 mL of hydro-chloric acid in a graduated cylinder, then pour it into thebeaker. Carefully rinse the graduated cylinder with distilledwater to clean out any leftover acid.Caution: Hydrochloric acid is corrosive. If any should spill onyou, immediately flush the area with water and notify yourteacher.

2. Add three drops of phenolphthalein indicator to the acid in thebeaker. You will not see anything happen yet because this indi-cator won’t show its color unless too much base is present.

3. Measure 20 mL of sodium hydroxide (base) in the graduatedcylinder, and add it slowly to the beaker with the acid. Usethe stirring rod to mix the substances completely.Caution: Sodium hydroxide is also corrosive. If any shouldspill on you, immediately flush the area with water and notifyyour teacher.

4. Use an eyedropper to add more base to the acid-basemixture in the beaker a few drops at a time. Be sure tostir the mixture after each few drops. Continue addingdrops of base until the mixture remains colored afterstirring.

5. Use another eyedropper to add acid tothe beaker, one drop at a time, until thecolor just disappears after stirring.

Chapter 15 LabBook

Materials• hydrochloric acid


• 100 mL beaker

• distilled water

• phenolphthalein solutionin a dropper bottle

• sodium hydroxide

• glass stirring rod

• 2 eyedroppers

• evaporating dish

• magnifying lens

SKILL BUILDER


691

6. Pour the mixture carefully into an evaporating dish, and placethe dish where your teacher tells you to allow the water toevaporate overnight.

7. The next day, examine your evaporating dish and study the crys-tals that were left with a magnifying lens. Identify the color,shape, and other properties that the crystals have.

Analysis

8. The equation for the reaction above is:

HCI NaOH H2O NaCI.

NaCl is ordinary table salt and forms veryregular cubic crystals that are white. Didyou find white cubic crystals?

9. The phenolphthalein indicator changescolor in the presence of a base. Whydid you add more acid in step 5 untilthe color disappeared?

Chapter 15 LabBook

Going FurtherAnother neutralization reaction occursbetween hydrochloric acid and potas-sium hydroxide, KOH. The equation forthis reaction is as follows:

HCl KOH H2O KCl

What are the products of this neutrali-zation reaction? How do they comparewith those you discovered in thisexperiment?


Materials• 15 dominoes

• stopwatch

Domino Chain ReactionsFission of uranium-235 is a process that relies on neutrons. Whena uranium-235 nucleus splits into two smaller nuclei, it releasestwo or three neutrons that can cause neighboring nuclei toundergo fission. This can result in a nuclear chain reaction. In this lab you will build two models of nuclear chain reactions using dominoes.


1. For the first model, set up the dominoes as shown below.Each domino should hit two dominoes in the next row whenpushed over.

2. Measure the time it takes for all of the dominoes to fall. Todo this, start the stopwatch as you tip over the front domino.Stop the stopwatch when the last domino falls. Record thistime in your ScienceLog.

3. If some of the dominoes do not fall, repeat steps 1 and 2. Youmay have to adjust the setup a few times.

4. For the second model, set up the dominoes as shown atright. The domino in the first row should hit both of thedominoes in the second row. Beginning with the second row,only one domino from each row should hit both of the domi-noes in the next row.

5. Repeat step 2. Again, you may have to adjust the setup a fewtimes to get all the dominoes to fall.


MAKING MODELS



6. Which model represents an uncontrolled chain reaction? Whichrepresents a controlled chain reaction? Explain your answers.

7. Imagine that each domino releases a certain amount ofenergy as it falls. Compare the total amount of energyreleased in the two models.

8. Compare the time needed to release the energy in the models.Which model was longest? Which model was shortest?

Draw Conclusions

9. In a nuclear power plant, a chain reaction is controlled by usinga material that absorbs neutrons. Only enough neutrons to con-tinue the chain reaction are allowed to produce further fissionof uranium-235. Explain how your model of a controllednuclear chain reaction modeled this process.

10. Why must uranium nuclei be close to each other in order fora nuclear chain reaction to occur? (Hint: What would happenin your model if the dominoes were too far apart?)

LabBook 693Copyright © by Holt, Rinehart and Winston. All rights reserved.

Ask a Question

1. How do electric charges build up onclothes in a dryer?

Form a Hypothesis

2. Write a statement that answers thequestion above. Explain your reasoning.

Test the Hypothesis

3. Tie a piece of thread approximately 30 cmin length to a packing peanut. Hang thepeanut by the thread from the edge of atable. Tape the thread to the table.

4. Rub the rubber rod with the wool cloth for10–15 seconds. Bring the rod near, but donot touch, the peanut. Observe the peanutand record your observations. If nothinghappens, repeat this step.

5. Touch the peanut with the rubber rod. Pullthe rod away from the peanut, and thenbring it near again. Record yourobservations.

6. Repeat steps 4 and 5 with the glass rodand silk cloth.


Materials• 30 cm thread

• plastic-foam packingpeanut

• tape

• rubber rod

• wool cloth

• glass rod

• silk cloth

Stop the Static Electricity!Imagine this scenario: Some of your clothes cling together whenthey come out of the dryer. This annoying problem is caused bystatic electricity—the buildup of electric charges on an object. Inthis lab, you’ll discover how this buildup occurs.

DISCOVERY LAB

7. Now rub the rubber rod with the woolcloth, and bring the rod near the peanutagain. Record your observations.

Analyze the Results

8. What caused the peanut to act differentlyin steps 4 and 5?

9. Did the glass rod have the same effect onthe peanut as the rubber rod did? Explainhow the peanut reacted in each case.

10. Was the reaction of the peanut the same insteps 5 and 7? Explain.

Draw Conclusions

11. Based on your results, was your hypothesiscorrect? Explain your answer, and write anew statement if necessary.

Communicate Results

12. Explain why the rubber rod and the glassrod affected the peanut.

Going FurtherDo some research to find out how a dryersheet helps stop the buildup of electric charges in the dryer.



Potato PowerHave you ever wanted to look inside a D cell from a flashlight or anAA cell from a portable radio? All cells include the same basic com-ponents, as shown below. There is a metal “bucket,” some electro-lyte (a paste), and a rod of some other metal (or solid) in themiddle. Even though the construction is simple, companies that manu-facture cells are always trying to make a product with the highestvoltage possible from the least expensive materials. Sometimes theytry different pastes, and sometimes they try different combinations ofmetals. In this lab, you will make your own cell. Using inexpensivematerials, you will try to produce the highest voltage you can.

Procedure

1. Choose two metal strips. Carefully pushone of the strips into the potato at least 2 cm deep. Insert the second strip thesame way, and measure how far apart thetwo strips are. (If one of your metal stripsis too soft to push into the potato, push aharder strip in first, remove it, and thenpush the soft strip into the slit.) Record thetwo metals you have used and the distancebetween the strips in your ScienceLog.Caution: The strips of metal may havesharp edges.

2. Connect the voltmeter to the two strips,and record the voltage.

3. Move one of the strips closer to or fartherfrom the other. Measure the new distanceand voltage. Record your results.

4. Repeat steps 1 through 3, using differentcombinations of metal strips and distancesuntil you find the combination that pro-duces the highest voltage.

Analysis

5. What combination of metals and distanceproduced the highest voltage?

6. If you change only the distance but use thesame metal strips, what is the effect on the voltage?

7. One of the metal strips tends to lose elec-trons, while the other tends to gain elec-trons. What do you think would happen ifyou used two strips of the same metal?

Materials• labeled metal strips

• potato

• metric ruler

• voltmeter

Metal “bucket”

Electrolyte

Metal or carbon rod

D cell


MAKING MODELS


Circuitry 101You have learned that there are two basic types of electrical circuits.A series circuit connects all the parts in a single loop, and a parallelcircuit connects each of the parts on separate branches to thepower source. If you want to control the whole circuit, the loadsand the switch must be wired in series. If you want parts of the cir-cuit to operate independently, the loads must be wired in parallel.

No matter how simple or complicated a circuit may be, Ohm’slaw (current equals voltage divided by resistance) applies. In this lab, you will construct both a series circuit and a parallel circuit. Youwill use an ammeter to measure current and a voltmeter to measurevoltage. With each circuit, you will test and apply Ohm’s law.

Part A—Series Circuit

Procedure

1. Construct a series circuit with a powersource, a switch, and three light bulbs.Caution: Always leave the switch openwhen constructing or changing the circuit.Close the switch only when you are testingor taking a reading.

2. Draw a diagram of your circuit in yourScienceLog.

3. Test your circuit. Do all three bulbs lightup? Are they all the same brightness? Whathappens if you carefully unscrew one lightbulb? Does it make any difference whichbulb you unscrew? Record your observa-tions in your ScienceLog.

4. Connect the ammeter between the powersource and the switch. Close the switch, andrecord the current with a label on your dia-gram in your ScienceLog. Be sure to showwhere you measured the current and whatthe value was.

5. Reconnect the circuit so the ammeter isbetween the first and second bulbs. Recordthe current, as you did in step 4.

6. Move the ammeter so it is between thesecond and third bulbs, and record thecurrent again.


Materials• power source—dry cell(s)

• switch

• 3 light-bulb holders

• 3 light bulbs

• insulated wire, cut into 15 cm lengths with bothends stripped

• ammeter

• voltmeter

SKILL BUILDER

7. Remove the ammeter from the circuit, andconnect the voltmeter to the two ends ofthe power source. Record the voltage witha label on your diagram.

8. Use the voltmeter to measure the voltageacross each bulb. Label the voltage acrosseach bulb on your diagram.

Part B—Parallel Circuit

Procedure

9. Take apart your series circuit, and reassem-ble the same power source, switch, andthree light bulbs so that the bulbs arewired in parallel. (Note: The switch mustremain in series with the power source tobe able to control the whole circuit.)



10. Draw a diagram of your parallel circuit inyour ScienceLog.

11. Test your circuit, and record your observa-tions, as you did in step 3.

12. Connect the ammeter between the powersource and the switch. Record the readingon your diagram.

13. Reconnect the circuit so that the ammeteris right next to one of the three bulbs.Record the current on your diagram.

14. Repeat step 13 for the two remainingbulbs.

15. Remove the ammeter from your circuit, andconnect the voltmeter to the two ends ofthe power source. Record this voltage.

16. Measure and record the voltage acrosseach light bulb.

Analysis—Parts A and B

17. Was the current the same at all places inthe series circuit? Was it the same every-where in the parallel circuit?

18. For each circuit, compare the voltage ateach light bulb with the power source.

19. What is the relationship between the volt-age at the power source and the voltagesat the light bulbs in a series circuit?

20. Use Ohm’s law and the readings for current (I)and voltage (V) at the power source for bothcircuits to calculate the total resistance (R) inboth the series and parallel circuits.

21. Was the total resistance for both circuitsthe same? Explain your answer.

22. Why did the bulbs differ in brightness?

23. Based on your results, what do you thinkmight happen if too many electric appli-ances are plugged into the same seriescircuit? the same parallel circuit?


Magnetic MysteryEvery magnet is surrounded by a magnetic field. Magnetic fieldlines show the shape of the magnetic field. These lines can bemodeled by using iron filings. The iron filings are affected by themagnetic field, and they fall into lines showing the field. In thislab, you will first learn about magnetic fields, and then you willuse this knowledge to identify a mystery magnet’s shape andorientation based on observations of the field lines.

Collect Data

1. Lay one of the magnets flat on a table.

2. Place a sheet of clear acetate over themagnet. Sprinkle some iron filings on theacetate to see the magnetic field lines.

3. In your ScienceLog, draw the magnet andthe magnetic field lines.

4. Remove the acetate, and pour the ironfilings back into the container.

5. Place your magnet so that one end ispointing up. Repeat steps 2 through 4.

6. Place your magnet on its side. Repeat steps2 through 4.

7. Repeat steps 1 through 6 with the othermagnet.


8. Create a magnetic mystery for another labteam by removing the lid from a shoe box,and taping a magnet underneath the lid.Orient the magnet so that determining theshape of the magnetic field and the orien-tation of the magnet will be challenging.Once the magnet is secure, place the lid on the box.

9. Exchange boxes with another team.

10. Without opening the box, use the sheet ofacetate and the iron filings to determinethe shape of the magnetic field of themagnet in the box.

11. Make a drawing of the magnetic field linesin your ScienceLog.


Draw Conclusions

12. Use your drawings from steps 1 through 7to identify the shape and orientation of themagnet in your magnetic mystery box.Draw a picture of your conclusion.

Going FurtherExamine your drawings. Can you identify thenorth and south poles of a magnet from theshape of the magnetic field lines? Design aprocedure that would allow you to determinethe poles of a magnet.

Materials• 2 magnets, different

shapes

• sheet of clear acetate

• iron filings

• shoe box

• masking tape

SKILL BUILDER


Electricity fromMagnetismYou use electricity every day. But did you ever wonder where itcomes from? Some of the electrical energy you use is convertedfrom chemical energy in cells or batteries. But what about whenyou plug a lamp into a wall outlet? In this lab, you will see howelectricity can be generated from magnetism.

Ask a Question


1. How can electricity be generated frommagnetism?

Form a Hypothesis

2. Write a statement to answer question 1.

Test the Hypothesis

3. Sand the enamel off of the last 2 or 3 cmof each end of the magnet wire. Wrap themagnet wire around the tube to make acoil as illustrated below. Attach the bareends of the wire to the galvanometer usingthe insulated wires.

4. While watching the galvanometer, move abar magnet into the coil, hold it there for amoment, and then remove it. Record yourobservations in your ScienceLog.

5. Repeat step 4 several times, moving themagnet at different speeds. Observe thegalvanometer carefully.

6. Hold the magnet still, and pass the coilover the magnet. Record your observations.

Analyze the Results

7. How does the speed of the magnet affectthe size of the electric current?

8. How is the direction of the electric currentaffected by the motion of the magnet?

9. Examine your hypothesis. Is your hypoth-esis accurate? Explain. If necessary, write anew hypothesis to answer question 1.

Draw Conclusions

10. Would an electric current still be generatedif the wire were broken? Why or why not?

11. Could a stationary magnet be used to gen-erate an electric current? Explain.

12. What energy conversions occur in thisinvestigation?

Communicate Results

13. Write a short paragraph that explains therequirements for generating electricity frommagnetism.

Materials• sandpaper

• 150 cm of magnet wire

• cardboard tube

• commercial galvanometer

• 2 insulated wires with alli-gator clips, each approxi-mately 30 cm long

• strong bar magnet

DISCOVERY LAB



Materials• 100 cm of magnet wire

• cardboard tube

• sandpaper

• 2 large paper clips

• 4 disk magnets

• plastic-foam cup

• tape

• 2 insulated wires withalligator clips, eachapproximately 30 cm long

• 4.5 V battery

• permanent marker

Build a DC MotorElectric motors can be used for many things. Hair dryers, CDplayers, and even some cars and buses are powered by electricmotors. In this lab, you will build a direct current electric motor—the basis for the electric motors you use every day.

Procedure

1. To make the armature for the motor, wind the wire around thecardboard tube to make a coil like the one shown below. Windthe ends of the wire around the loops on each side of the coil.Leave about 5 cm free on each end.

2. Hold the coil on its edge. Sand the enamel from only the tophalf of each end of the wire. This acts like a commutator, exceptthat it blocks the electric current instead of reversing it duringhalf of each rotation.

3. Partially unfold the two paper clips from the middle. Make ahook in one end of each paper clip to hold the coil, as shownat right.

4. Place two disk magnets in the bottom of the cup,and place the other magnets on the outside ofthe bottom of the cup. The magnets shouldremain in place when the cup is turnedupside down.

5. Tape the paper clips to the sides of thecup. The hooks should be at the sameheight, and should keep the coil fromhitting the magnet.

6. Test your coil. Flick the top of the coil lightly withyour finger. The coil should spin freely withoutwobbling or sliding to one side.

7. Make adjustments to the ends of the wireand the hooks until your coil spins freely.

8. Use the alligator clips to attach one wire toeach paper clip.

9. Attach the free end of one wire to oneterminal of the battery.


MAKING MODELS

CoilPaper clip

Disc magnet

Cup

Tape

Alligatorclip

Wire

Paper clip



Collect Data

10. Connect the free end of the other wire to the second battery terminal and giveyour coil a gentle spin. Record yourobservations.

11. Stop the coil and give it a gentle spin in the opposite direction. Record yourobservations.

12. If the coil does not keep spinning, checkthe ends of the wire. Bare wire shouldtouch the paper clips during half of thespin, and only enamel should touch thepaper clips for the other half of the spin.

13. If you removed too much enamel, colorhalf of the wire with a permanent marker.

14. Switch the connections to the battery andrepeat steps 10 and 11.

Analyze the Results

15. Did your motor always spin in the directionyou started it? Explain.

16. Why was the motor affected by switchingthe battery connections?

17. Some electric cars run on solar power.Which part of your model wouId bereplaced by the solar panels?

Draw Conclusions

18. Some people claim that electric-poweredcars are cleaner than gasoline-poweredcars. Explain why this might be true.

19. List some reasons that electric cars are notideal. (Hint: What happens to batteries?)

20. How could your model be used to helpdesign a hair dryer?

21. Make a list of at least three other itemsthat could be powered by an electric motorlike the one you built.


Materials• diode

• 2 m of insulated wire

• 2 cardboard tubes

• tape

• scissors

• aluminum foil

• sheet of paper

• 7 connecting wires, 30 cmeach

• 3 paper clips

• cardboard, 20 30 cm

• antenna

• ground wire

• earphone

Tune In!You probably have listened to radios many times in your life.Modern radios are complicated electronic devices. However, radiosdo not have to be so complicated. The basic parts of all radiosinclude: a diode, an inductor, a capacitor, an antenna, a groundwire, and an earphone (or a speaker and amplifier on a largeradio). In this activity, you will examine each of these componentsone at a time as you build a working model of a radio-wavereceiver.

Procedure

1. Examine the diode. Describe it in your ScienceLog.

2. A diode carries current in only one direction. Draw the inside ofa diode in your ScienceLog, and illustrate how this might occur.

3. An inductor controls the amount of electric current due to theresistance of the wire. Make an inductor by winding the insu-lated wire around a cardboard tube approximately 100 times.Wind the wire so that all the turns of the coil are neat and inan orderly row, as shown below. Leave about 25 cm of wireon each end of the coil. The coil of wire may be held on thetube using tape.

4. Now you will construct the variable capacitor. A capacitorstores electrical energy when an electric current is applied. A variable capacitor is a capacitor in which the amount ofenergy stored can be changed. Cut a piece of aluminum foilto go around the tube but only half the length of the tube, asshown on the next page. Keep the foil as wrinkle-free as pos-sible as you wrap it around the tube, and tape the foil toitself. Now tape the foil to the tube.

5. Use the sheet of paper and tape to make a sliding cover onthe tube. The paper should completely cover the foil on thetube with about 1 cm extra.


MAKING MODELS



6. Cut another sheet of aluminum foil to wrap completelyaround the paper. Leave approximately 1 cm of paper show-ing at each end of the foil. Tape this foil sheet to the papersleeve. If you have done this correctly, you have a paper/foilsheet which will slide up and down the tube over the station-ary foil. The two pieces of foil should not touch.

7. Stand your variable capacitor on its end so that the stationaryfoil is at the bottom. The amount of stored energy is greaterwhen the sleeve is down than when the sleeve is up.

8. Use tape to attach one connecting wire to the stationary foilat the end of the tube. Use tape to attach another connectingwire to the sliding foil sleeve. Be sure that the metal part ofthe wire touches the foil.

9. Hook three paper clips on one edge of the cardboard, asshown below. Label one paper clip A, another B, and thethird one C.

10. Lay the inductor on the piece of cardboard, and tape it to thecardboard.

11. Stand the capacitor next to the inductor, and tape the tube tothe cardboard. Be sure not to tape the sleeve—it must be freeto slide.

Partially Completed Model Receiver

Inductor

Capacitor

Diode

Capacitor

Foil

Paper andfoil sleeve

Cardboardtube


12. Use tape to connect the diode to paper clips A and B. Thecathode should be closest to paper clip B. (The cathode endof the diode is the one with the dark band.) Make sure thatall connections have good metal-to-metal contact.

13. Connect one end of the inductor to paper clip A, and theother end to paper clip C. Use tape to hold the wires inplace.

14. Connect the wire from the sliding part of the capacitor topaper clip A. Connect the other wire (from the stationary foil)to paper clip C.

15. The antenna receives radio waves transmitted by a radio sta-tion. Tape a connecting wire to your antenna. Then connectthis wire to paper clip A.

16. Use tape to connect one end of the ground wire to paper clipC. The other end of the ground wire should be connected toan object specified by your teacher.


A Completed Model Receiver!

Antenna

Ground wire

Earphone



17. The earphone will allow you to detect the radio waves youreceive. Connect one wire from the earphone to paper clip Band the other wire to paper clip C.

18. You are now ready to begin listening. With everything con-nected, and the earphone in your ear, slowly slide the paper/foil sheet of the capacitor up and down. Listen for a very faintsound. You may have to troubleshoot many of the parts to getyour receiver to work. As you troubleshoot, check to be surethere is good contact between all the connections.

Analysis

19. Describe the process of operating your receiver.

20. Considering what you have learned about a diode, why is itimportant to have the diode connected the correct way?

21. A function of the inductor on a radio is to “slow the currentdown.” Why does the inductor you made slow the currentdown more than does a straight wire the length of your coil?

22. A capacitor consists of any two conductors separated by aninsulator. For your capacitor, list the two conductors and theinsulator.

23. Explain why the amount of stored energy is increased whenyou slide the foil sleeve down and decreased when thesleeve is up.

24. In your ScienceLog, make a list of ways that your receiver issimilar to a modern radio. Make a second list of ways thatyour receiver is different from a modern radio.


Materials• shallow pan, approximately

20 30 cm

• newspaper

• small beaker

• water

• 2 pencils

• stopwatch

Wave Energy and SpeedIf you threw a rock into a pond, waves would carry energy awayfrom the point of origin. But if you threw a large rock into a pond,would the waves carry more energy away from the point of originthan waves created by a small rock? And would a large rock cre-ate waves that move faster than waves created by a small rock? In this lab you’ll answer these questions.

Ask a Question

1. In this lab you will answer the following questions: Do wavescreated by a large disturbance carry more energy than wavescreated by a small disturbance? Do waves created by a largedisturbance travel faster than waves created by a smalldisturbance?

Form a Hypothesis

2. In your ScienceLog, write a few sentences that answer thequestions above.

Test the Hypothesis

3. Place the pan on a few sheets of newspaper. Using the smallbeaker, fill the pan with water.

4. Make sure that the water is still. Tap the surface of the waternear one end of the pan with the eraser end of one pencil.This represents the small disturbance. In your ScienceLog,record your observations aboutthe size of the waves that arecreated and the path they take.

5. Repeat step 4. This time, use thestopwatch to measure the timeit takes for one of the waves toreach the other side of the pan.Record your data in yourScienceLog.

6. Repeat steps 4 and 5 using twopencils at once. This representsthe large disturbance. (Try to usethe same amount of force to tapthe water as you did with justone pencil.)


DISCOVERY LAB



Analyze the Results

7. Compare the appearance of the waves cre-ated by one pencil with that of the wavescreated by two pencils. Were there anydifferences in amplitude (wave height)?

8. Compare the amount of time required forthe waves to reach the side of the pan.Did the waves travel faster when twopencils were used?

Draw Conclusions

9. Do waves created by a large disturbancecarry more energy than waves created by asmall disturbance? Explain your answerusing your results to support your answer.(Hint: Remember the relationship betweenamplitude and energy.)

10. Do waves created by a large disturbancetravel faster than waves created by a smalldisturbance? Explain your answer.

Going FurtherA tsunami is a giant ocean wave that can reacha height of 30 m. Tsunamis that reach land cancause injury and enormous property damage.Using what you learned in this lab about waveenergy and speed, explain why tsunamis are sodangerous. How do you think scientists canpredict when tsunamis will reach land?


Materials• coiled spring toy

• meterstick

• stopwatch

Wave Speed, Frequency,and WavelengthWave speed, frequency, and wavelength are three related prop-erties of waves. In this lab you will make observations and collectdata to determine the relationship among these properties.

Part A—Wave Speed

Procedure


2. On the floor or a table, two students should stretch the springto a length of 2 to 4 m. A third student should measure thelength of the spring. Record the length in Table 1.

3. One student should pull part of the spring sideways with onehand, as shown at right, and release the pulled-back portion.This will cause a wave to travel down the spring.

4. Using a stopwatch, the third student should measurehow long it takes for the wave to travel down thelength of the spring and back. Record this time inTable 1.

5. Repeat steps 3 and 4 two more times.


6. Calculate and record the wave speed foreach trial. (Hint: Speed equals distancedivided by time; distance is twice thespring length.)

7. Calculate and record the average timeand the average wave speed.


SKILL BUILDER

Trial Length of Time for Speed ofspring (m) wave (s) wave (m/s)

1

2

3

Average

Table 1 Wave Speed Data



Part B—Wavelength and Frequency

Procedure

8. Keep the spring the same length that you used in Part A.


10. One of the two students holding the spring should start shak-ing the spring from side to side until a wave pattern appearsthat resembles one of those shown below.

11. Using the stopwatch, the third group member should measureand record how long it takes for 10 cycles of the wave patternto occur. (One back-and-forth shake is one cycle.) Keep the pat-tern going so that measurements for three trials can be made.


12. Calculate the frequency for each trial by dividing the number ofcycles (10) by the time. Record the answers in Table 2.

13. Determine the wavelength using the equation at right thatmatches your wave pattern. Record your answer in Table 2.

14. Calculate and record the average time and frequency.

Draw Conclusions—Parts A and B

15. To discover the relationship among speed, wavelength, andfrequency, try multiplying or dividing any two of them to seeif the result equals the third. (Use the average speed, wave-length, and average frequency from your data tables.) In yourScienceLog, write the equation that shows the relationship.

16. Reread the definitions for frequency and wavelength in thechapter titled “The Energy of Waves.” Use these definitions toexplain the relationship that you discovered.

Trial Length of Time for Wave Wavelengthspring (m) 10 cycles (s) frequency (Hz) (m)

1

2

3

Average

Wave Patterns

Table 2 Wavelength and Frequency Data

Wavelength 2 length

Wavelength length

Wavelength 2/3 length


Materials• 4 tuning forks of different

frequencies

• pink rubber eraser

• meterstick

• graph paper

Easy ListeningPitch describes how low or high a sound is. A sound’s pitch isrelated to its frequency—the number of waves per second.Frequency is expressed in hertz (Hz), where 1 Hz equals onewave per second. Most humans can hear frequencies from 20 Hzto 20,000 Hz. However, not everyone detects all pitches equallywell at all distances. In this activity you will collect data to seehow well you and your classmates hear different frequencies atdifferent distances.

Ask a Question

1. Do students in your classroom hear low-, mid-, or high-frequency sounds better?

Form a Hypothesis

2. In your ScienceLog, write a hypothesis that answers thequestion above. Explain your reasoning.

Test the Hypothesis

3. Choose one member of your group to be the sound maker.The others will be the listeners.

4. Copy the data table below into your ScienceLog. Be sure toinclude a column for every listener in your group.

5. Record the frequency of one of the tuning forks in the toprow of the first column of the data table.


Distance (m)

Frequency Listener 1 Listener 2 Listener 3 Average

1 (___Hz)

2 (___Hz)

3 (___Hz)

4 (___Hz)

DISCOVERY LAB





6. The listeners should stand in front of the sound maker withtheir backs turned.

7. The sound maker will create a sound by striking the tip of thetuning fork gently with the eraser.

8. The listeners who hear the sound should take one step awayfrom the sound maker. The listeners who do not hear thesound should stay where they are.

9. Repeat steps 7 and 8 until none of the listeners can hear thesound or the listeners reach the edge of the room.

10. Using the meterstick, the sound maker should measure the dis-tance from his or her position to each of the listeners. All groupmembers should record this data in their tables.

11. Repeat steps 5 through 10 with a different tuning fork.

12. Continue until all four tuning forks have been tested.

Analyze the Results

13. Calculate the average distance for each frequency. Share yourgroup’s data with the rest of the class to make a data table forthe whole class.

14. Calculate the average distance foreach frequency for the class.

15. Make a graph of the class results,plotting average distance (y-axis)versus frequency (x-axis).

Draw Conclusions

16. Was everyone in the class able tohear all frequencies equally? (Hint:Was the average distance for eachfrequency the same?)

17. If the answer to question 16 is no,which frequency had the largestaverage distance? Which frequencyhad the smallest average distance?

18. Based on your graph, do yourresults support your hypothesis?Explain your answer.

19. Do you think your class sample islarge enough to confirm yourhypothesis for all humans of allages? Explain your answer.


Materials• materials of your choice,

approved by your teacher

The Speed of SoundIn the chapter titled “The Nature of Sound,” you learned that thespeed of sound in air is 343 m/s at 20°C (approximately roomtemperature). In this lab you’ll design an experiment to measurethe speed of sound yourself—and you’ll determine if you’re “up to speed”!

Procedure

1. Brainstorm with your teammates to comeup with a way to measure the speed ofsound. Consider the following as youdesign your experiment:

a. You must have a method of making asound. Some simple examples includespeaking, clapping your hands, andhitting two boards together.

b. Remember that speed is equal to dis-tance divided by time. You must devisemethods to measure the distance that a sound travels and to measure theamount of time it takes for that soundto travel that distance.

c. Sound travels very rapidly. A sound fromacross the room will reach your earsalmost before you can start recordingthe time! You may wish to have thesound travel a long distance.

d. Remember that sound travels in waves.Think about the interactions of soundwaves. You might be able to includethese interactions in your design.

2. Discuss your experimental design with yourteacher, including any equipment youneed. Your teacher may have questionsthat will help you improve your design.


3. Once your design is approved, carry outyour experiment. Be sure to perform sev-eral trials. Record your results in yourScienceLog.

Draw Conclusions

4. Was your result close to the value given inthe introduction to this lab? If not, whatfactors may have caused you to get such adifferent value?

5. Why was it important for you to performseveral trials in your experiment?


6. Compare your results with those of yourclassmates. Determine which experimentaldesign provided the best results. In yourScienceLog, explain why you think thisdesign was so successful.

Chapter 21712

DESIGNYOUR OWN


Tuneful TubeIf you have seen a singer shatter a crystal glass simply by singinga note, you have seen an example of resonance. For this to hap-pen, the note has to match the resonant frequency of the glass. Acolumn of air within a cylinder can also resonate if the air columnis the proper length for the frequency of the note. In this lab youwill investigate the relationship between the length of an air col-umn, the frequency, and the wavelength during resonance.

Procedure

1. Copy the data table below into your ScienceLog.

2. Fill the graduated cylinder with water.

3. Hold a plastic tube in the water so that about 3 cm is abovethe water.

4. Record the frequency of the first tuning fork. Gently strike thetuning fork with the eraser, and hold it so that the prongs arejust above the tube, as shown at right. Slowly move the tubeand fork up and down until you hear the loudest sound.

5. Measure the distance from the top of the tube to the water.Record this length in your data table.

6. Repeat steps 3–5 using the other three tuning forks.

Analysis

7. Calculate the wavelength (in centimeters) of each soundwave by dividing the speed of sound in air (343 m/s at20°C) by the frequency and multiplying by 100.

8. Make the following graphs: air column length versus fre-quency and wavelength versus frequency. On both graphs,plot the frequency on the x-axis.

9. Describe the trend between the length of the air columnand the frequency of the tuning fork.

10. How are the pitches you heard related to the wavelengthsof the sounds?


Materials• 100 mL graduated cylinder

• water

• plastic tube, supplied byyour teacher

• metric ruler

• 4 tuning forks of differentfrequencies


• graph paperData Collection Table

Frequency (Hz)

Length (cm)

SKILL BUILDER


The Energy of SoundIn the chapter titled “The Nature of Sound,” you learned aboutvarious properties and interactions of sound. In this lab you willperform several activities that will demonstrate that the propertiesand interactions of sound all depend on one thing—the energycarried by sound waves.

Part B—Resonance

Procedure

3. Strike a tuning fork with the eraser. Quickly pick up a secondtuning fork in your other hand and hold it about 30 cm fromthe first tuning fork.

4. Place the first tuning fork against your leg to stop its vibration.Listen closely to the second tuning fork. Record your observa-tions, including the frequencies of the two tuning forks.

5. Repeat steps 3 and 4, using the remaining tuning fork as the second tuning fork.

Analysis

6. Explain why you can hear a sound from the second tuningfork when the frequencies of the tuning forks used are the same.

7. When using tuning forks of different frequencies, would youexpect to hear a sound from the second tuning fork if youstrike the first tuning fork harder? Explain your reasoning.


Part A—Sound Vibrations

Procedure

1. Lightly strike a tuning fork with the eraser. Slowly place theprongs of the tuning fork in the plastic cup of water. Recordyour observations in your ScienceLog.

Analysis

2. How do your observations demonstrate that sound waves arecarried through vibrations?

Materials• 2 tuning forks of the same

frequency and one of adifferent frequency


• small plastic cup filledwith water

• rubber band

• 50 cm string

SKILL BUILDER



Part C—Interference

Procedure

8. Using the two tuning forks with the samefrequency, place a rubber band tightly overthe prongs near the base of one tuningfork. Strike both tuning forks at the sametime against the eraser. Hold a tuning fork3 to 5 cm from each ear. If you cannothear any differences, move the rubberband down further on the prongs. Strikeagain. Record your observations in yourScienceLog.

Analysis

9. Did you notice the sound changing backand forth between loud and soft? A steadypattern like this is called a beat frequency.Explain this changing pattern of loudnessand softness in terms of interference (bothconstructive and destructive).

Part D—The Doppler Effect

Procedure

10. Your teacher will tie the piece of stringsecurely to the base of one tuning fork.Your teacher will then strike the tuning forkand carefully swing the tuning fork in a cir-cle overhead. Record your observations inyour ScienceLog.

Analysis

11. Did the tuning fork make a different soundwhen your teacher was swinging it thanwhen he or she was holding it? If yes,explain why.

12. Is the actual pitch of the tuning fork chang-ing? Explain.

Draw Conclusions—Parts A–D

13. Explain how your observations from eachpart of this lab verify that sound wavescarry energy from one point to anotherthrough a vibrating medium.

14. Particularly loud thunder can cause thewindows of your room to rattle. How is thisevidence that sound waves carry energy?


What Color of Light IsBest for Green Plants?Plants grow well outdoors under natural sunlight. However, someplants are grown indoors under artificial light. A wide variety ofcolored lights are available for helping plants grow indoors. In thisexperiment, you’ll test several colors of light to discover whichcolor best meets the energy needs of green plants.

Ask a Question

1. What color of light is the best for growinggreen plants?

Form a Hypothesis

2. In your ScienceLog, write a hypothesis thatanswers the question above. Explain yourreasoning.

Test the Hypothesis

3. Use the masking tape and marker to labelthe side of each Petri dish with your nameand the type of light you will place the dishunder.

4. Place a moist paper towel in each Petridish. Place five seedlings on top of thepaper towel. Cover each dish.

5. Record your observations of the seedlings,such as length, color, and number ofleaves, in your ScienceLog.

6. Place each dish under the appropriate light.

7. Observe the Petri dishes every day for atleast 5 days. Record your observations inyour ScienceLog.

Analyze the Results

8. Based on your results, which color of lightis the best for growing green plants? Whichcolor of light is the worst?


Draw Conclusions

9. Remember that the color of an opaqueobject (such as a plant) is determined by thecolors the object reflects. Use this informa-tion to explain your answer to question 8.

10. Would a purple light be good for growingpurple plants? Explain.

Communicate Results

11. Write a short paragraph summarizing yourconclusions.

Materials• masking tape

• marker

• Petri dishes and covers

• water

• paper towels

• bean seedlings

• variety of colored lights,supplied by your teacher

DISCOVERY LAB



Which Color Is Hottest?Will a navy blue hat or a white hat keep your head warmer incool weather? Colored objects absorb energy, which can make theobjects warmer. How much energy is absorbed depends on theobject’s color. In this experiment you will test several colors undera bright light to determine which colors absorb the most energy.

Procedure

1. Copy the table below into your ScienceLog. Be sure to haveone column for each color of paper you have and enoughrows to end at 3 minutes.

717

2. Tape a piece of colored paper around thebottom of a thermometer and hold itunder the light source. Record the tem-perature every 15 seconds for 3 minutes.

3. Cool the thermometer by removing thepiece of paper and placing the thermom-eter in the cup of room-temperature water.After 1 minute, remove the thermometer,and dry it with a paper towel.

4. Repeat steps 2 and 3 with each color, mak-ing sure to hold the thermometer at thesame distance from the light source.

Analyze the Results

5. Prepare a graph of temperature (y-axis)versus time (x-axis). Plot all data onone graph using a different coloredpencil or pen for each set of data.

6. Rank the colors you used inorder from hottest to coolest.

Draw Conclusions

7. Compare the colors based on the amountof energy each absorbs.

8. In this experiment a white light was used.How would your results be different if youused a red light? Explain.

9. Use the relationship between color andenergy absorbed to explain why differentcolors of clothing are used for differentseasons.

Materials• tape

• squares of colored paper

• thermometer

• light source

• cup of room-temperaturewater

• paper towels

• graph paper

• colored pencils or pens

DISCOVERY LAB

Time (s) White Red Blue Black

0

15

30

45

etc.



Materials

Part A

• 3 flashlights

• colored filters—red, green,and blue

• masking tape

• white paper

Part B

• masking tape

• 2 small plastic or papercups

• water

• paintbrush

• watercolor paints

• white paper

• metric ruler

Mixing ColorsWhen you mix two colors, like red and green, you create a differ-ent color. But what color do you create? And is that new colorbrighter or darker? The color and brightness you see depend onthe light that reaches your eye, and that depends on whether youare performing color addition (combining wavelengths by mixingcolors of light) or color subtraction (absorbing light by mixing col-ors of pigments). In this experiment, you will try both types ofcolor formation and see the results firsthand!

Part A—Color Addition

Procedure

1. Place a colored filter over each flashlight lens. Use maskingtape to hold the filters in place.

2. In a darkened room, shine the red light on a sheet of cleanwhite paper. Then shine the blue light next to the red light.You should see two circles of light, one red and one blue,next to each other.

3. Move the flashlights so that the circles overlap by about halftheir diameter. Examine the three areas of color, and recordyour observations. What color is formed in the mixed area? Isthe mixed area brighter or darker than the single-color areas?

4. Repeat steps 2 and 3 with the red and green lights.

5. Now shine all three lights at the samepoint on the sheet of paper. Examine theresults, and record your observations.

Analysis

6. In general, when you mixed two colors,was the result brighter or darker than theoriginal colors?

7. In step 5, you mixed all three colors. Wasthe resulting color brighter or darker thanmixing two colors? Explain your answer in terms of color addition. (Hint: Read the definition of color addition in theintroduction.)

8. Based on your results, what do you thinkwould happen if you mixed all the colorsof light? Explain.


SKILL BUILDER

Red Green?



Part B—Color Subtraction

Procedure

9. Place a piece of masking tape on each cup. Label one cup“Clean” and the other cup “Dirty.” Fill both cups approximatelyhalf full with water.

10. Wet the paintbrush thoroughlyin the “Clean” cup. Using thewatercolor paints, paint a redcircle on the white paper. Thecircle should be approximately4 cm in diameter.

11. Clean the brush by rinsing it firstin the “Dirty” cup and then inthe “Clean” cup.

12. Paint a blue circle next to thered circle. Then paint half thered circle with the blue paint.

13. Examine the three areas: red, blue, and mixed. What color isthe mixed area? Does it appear brighter or darker than thered and blue areas? Record your observations in yourScienceLog.

14. Clean the brush. Paint a green circle 4 cm in diameter, andthen paint half the blue circle with green paint.

15. Examine the green, blue, and mixed areas. Record your observations.

16. Now add green paint to the mixed red-blue area, so that youhave an area that is a mixture of red, green, and blue paint.Clean your brush.

17. Record your observations of this new mixed area.

Analysis

18. In general, when you mixed two colors, was the resultbrighter or darker than the original colors?

19. In step 16, you mixed all three colors. Was the result brighteror darker than mixing two colors? Explain your answer interms of color subtraction. (Hint: Read the definition of colorsubtraction in the introduction.)

20. Based on your results, what do you think would happen ifyou mixed all the colors of paint? Explain.


Materials• convex mirror

• concave mirror

• candle

• jar lid

• modeling clay

• matches

• index card

Mirror ImagesWhen light actually passes through an image, the image is a realimage. When light does not pass through the image, the image isa virtual image. Recall that plane mirrors produce only virtualimages because the image appears to be behind the mirror whereno light can pass through it.

In fact, all mirrors can form virtual images, but only some mir-rors can form real images. In this experiment, you will explore thevirtual images formed by concave and convex mirrors, and youwill try to find a real image using both types of mirrors.

Part A—Finding Virtual Images

Make Observations

1. Hold the convex mirror at arm’s length away from your face.Observe the image of your face in the mirror.

2. Slowly move the mirror toward your face, and observe whathappens to the image. Record your observations in yourScienceLog.

3. Move the mirror very close to your face. Record your observa-tions in your ScienceLog.

4. Slowly move the mirror away from your face, and observe whathappens to the image. Record your observations.

5. Repeat steps 1 through 4 with the concave mirror.


6. For each mirror, did you find a virtualimage? How can you tell?

7. Describe the images you found. Were theysmaller, larger, or the same size as your face?Were they upright or inverted?

Draw Conclusions

8. Describe at least one use for each type of mirror. Be creative,and try to think of inventions that might use the properties ofthe two types of mirrors.


SKILL BUILDER



Part B—Finding a Real Image

Make Observations

9. In a darkened room, place a candle in a jar lid near one endof a table. Use modeling clay to hold the candle in place.Light the candle. Caution: Use extreme care around an open flame.

10. Use more modeling clay to make a base to hold the convexmirror upright. Place the mirror at the other end of the table,facing the candle.

11. Hold the index card between the candle and the mirror butslightly to one side so that you do not block the candlelight,as shown below.

12. Move the card slowly from side to side and back and forth tosee whether you can focus an image of the candle on it.Record your results in your ScienceLog.

13. Repeat steps 10–12 with the concave mirror.


14. For each mirror, did you find a real image? How can you tell?

15. Describe the real image you found. Was it smaller, larger, orthe same size as the object? Was it upright or inverted?

Draw Conclusions

16. Astronomical telescopes use large mirrors to reflect light to forma real image. Based on your results, would a concave or convexmirror be better for this instrument? Explain your answer.


Materials• index card

• modeling clay

• candle

• jar lid

• matches

• convex lens

• meterstick

Images from ConvexLensesA convex lens is thicker in the center than at the edges. Light rayspassing through a convex lens come together at a point. Undercertain conditions, a convex lens will create a real image of anobject. This image will have certain characteristics, depending onthe distance between the object and the lens. In this experimentyou will determine the characteristics of real images created by aconvex lens—the kind of lens used as a magnifying lens.

Ask a Question

1. What are the characteristics of real images created by a con-vex lens? How do these characteristics depend on the loca-tion of the object and the lens?



3. Use some modeling clay to make a base for the lens. Placethe lens and base in the middle of the table.

722

DISCOVERY LAB

Orientation Size Image distance Object distanceImage (upright/inverted) (larger/smaller) (cm) (cm)

1

2

3

Chapter 23 LabBook

Data Collection




4. Stand the index card upright in some mod-eling clay on one side of the lens.

5. Place the candle in the jar lid, and anchor itwith some modeling clay. Place the candle onthe table so that the lens is halfway betweenthe candle and the card. Light the candle.Caution: Use extreme care around an openflame.

Collect Data

6. In a darkened room, slowly move the cardand the candle away from the lens whilekeeping the lens exactly halfway betweenthe card and the candle. Continue until yousee a clear image of the candle flame onthe card. This is image 1.

7. Measure and record the distance betweenthe lens and the card (image distance) andbetween the lens and the candle (objectdistance).

8. Is image 1 upright or inverted? Is it largeror smaller than the candle? Record thisinformation in the table.

9. Slide the lens toward the candle to get anew image (image 2) of the candle on thecard. Leave the lens in this position.

10. Repeat steps 7 and 8 for image 2.

11. Move the lens back to the middle, andthen move the lens toward the card to geta third image (image 3).

12. Repeat steps 7 and 8 for image 3.


13. Describe the trend between image distanceand image size.

14. What are the similarities between the realimages formed by a convex lens?

Draw Conclusions

15. The lens of your eye is a convex lens. Usethe information you collected to describethe image projected on the back of youreye when you look at an object.

16. Convex lenses are used in film projectors.Explain why your favorite movie stars aretruly “larger than life” on the screen interms of the image distance and the objectdistance.


17. Write a paragraph to summarize youranswer to the question in step 1. Be sureto include the roles that image distanceand object distance have in determiningthe characteristics of the images.


Self-Check Answers724

SE

LF

-CH

EC

K

Self-Check AnswersChapter 1—The World of Physical SciencePage 16: flapping rate

Chapter 2—The Properties of MatterPage 41: approximately 30 N

Chapter 3—States of MatterPage 64: The pressure would increase.

Page 70: endothermic

Chapter 4—Elements, Compounds, andMixtures

Page 87: No, the properties of pure water are the same nomatter what its source is.

Page 93: Copper and silver are solutes. Gold is the solvent.

Chapter 5—Matter in MotionPage 110: Numbers 1 and 3 are examples of velocity.

Page 117: 2 N north

Page 122: sliding friction

Page 126: Gravity is a force of attraction between objects thatis due to the masses of the objects.

Chapter 6—Forces in MotionPage 140: A leaf is more affected by air resistance.

Page 147: This can be answered in terms of either Newton’sfirst law or inertia.

Newton’s first law: When the bus is still, both you and thebus are at rest. The bus started moving, but no unbalancedforce acted on your body, so your body stayed at rest.

Inertia: You have inertia, and that makes you difficult tomove. As a result, when the bus started to move, you didn’tmove with it.

Chapter 7—Forces in FluidsPage 175: Air travels faster over the top of a wing.

Chapter 8—Work and MachinesPage 189: Pulling a wheeled suitcase is doing work becausethe force applied and the motion of the suitcase are in thesame direction.


Self-Check Answers 725

SE

LF

-CH

EC

KChapter 9—Energy and Energy ResourcesPage 223: A roller coaster has the greatest potential energy atthe top of the highest hill (usually the first hill) and the great-est kinetic energy at the bottom of the highest hill.

Chapter 10—Heat and Heat TechnologyPage 259: Two substances can have the same temperature butdifferent amounts of thermal energy because temperature,unlike thermal energy, does not depend on mass. A smallamount of a substance at a particular temperature will haveless thermal energy than a large amount of the substance atthe same temperature.

Page 261: Steam can cause a more severe burn than boilingwater because steam contains more energy per unit mass thandoes boiling water.

Chapter 11—Introduction to AtomsPage 285: The particles Thomson discovered had negativecharges. Because an atom has no charge, it must contain posi-tively charged particles to cancel the negative charges.

Chapter 12—The Periodic TablePage 312: It is easier for atoms of alkali metals to lose oneelectron than for atoms of alkaline-earth metals to lose twoelectrons. Therefore, alkali metals are more reactive thanalkaline-earth metals.

Chapter 13—Chemical BondingPage 333: neon

Page 337: 1. 6 2. In a covalent bond, electrons are sharedbetween atoms. In an ionic bond, electrons are transferredfrom one atom to another.

Chapter 14—Chemical ReactionsPage 353: 2 sodium atoms, 1 sulfur atom, and 4 oxygen atoms

Page 355: CaBr2 + Cl2 → Br2 + CaCl2

reactants: CaBr2 and Cl2

products: Br2 and CaCl2

Chapter 15—Chemical CompoundsPage 381: a soft drink

Chapter 16—Atomic EnergyPage 400: alpha particles


Self-Check Answers726

SE

LF

-CH

EC

K

Chapter 17—Introduction to ElectricityPage 425: Plastic wrap is charged by friction as it is pulledoff the roll.

Page 438: E = P t; E = 200 W 2 h = 400 Wh

Students will have to use data from the table on page 438 toanswer this question.

Page 441: Yes; a microwave oven is an example of a loadbecause it uses electrical energy to do work.

Chapter 18—ElectromagnetismPage 464: No; an electromagnet is produced when the mag-netic field of the coil of wire causes the domains in the core toline up. Wood does not contain domains and therefore cannotbe the core of an electromagnet.

Chapter 19—Electronic TechnologyNo self-check question for this chapter.

Chapter 20—The Energy of WavesPage 512: Mechanical waves require a medium; electromag-netic waves do not.

Page 521: A light wave will not refract if it enters a newmedium perpendicular to the surface because the entire waveenters the new medium at the same time.

Chapter 21—The Nature of SoundPage 549: A person hears a sonic boom when a shock wavereaches his or her ears. If two people are standing a block ortwo apart, the shock wave will reach them at different times, sothey will hear sonic booms at different times.

Page 553: Interference is the most important wave interactionfor determining sound quality.

Chapter 22—The Nature of LightPage 583: The paper will appear blue because only blue lightis reflected from the paper.

Chapter 23—Light and Our WorldPage 602: Concave lenses do not form real images. Only areal image can be magnified by another lens, such as the eyepiece lens.


Appendix 727

AP

PE

ND

IX

CONTENTS

Concept Mapping . . . . . . . . . . . . . . . . . . . . . . . . . 728

SI Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . 729

Temperature Scales . . . . . . . . . . . . . . . . . . . . . . . 730

Measuring Skills . . . . . . . . . . . . . . . . . . . . . . . . . 731

Scientific Method . . . . . . . . . . . . . . . . . . . . . . . . . 732

Making Charts and Graphs . . . . . . . . . . . . . . . . . . 735

Math Refresher . . . . . . . . . . . . . . . . . . . . . . . . . . . 738

Physical Science Refresher . . . . . . . . . . . . . . . . . . 742

Periodic Table of the Elements . . . . . . . . . . . . . . . 744

Physical Science Laws and Principles . . . . . . . . . . 746

Inch

Fathom

Yard

Foot


Appendix728

AP

PE

ND

IX

How to Make a Concept MapMake a list of the main ideas or concepts.

It might help to write each concept on itsown slip of paper. This will make it easier torearrange the concepts as many times asnecessary to make sense of how the con-cepts are connected. After you’ve made afew concept maps this way, you can godirectly from writing your list to actuallymaking the map.

Arrange the concepts in order from themost general to the most specific.

Put the most general concept at the topand circle it. Ask yourself, “How does thisconcept relate to the remaining concepts?”As you see the relationships, arrange theconcepts in order from general to specific.

Connect the related concepts with lines.

On each line, write an action word orshort phrase that shows how the con-cepts are related.

Look at the concept maps on this page,and then see if you can make one for the following terms:

plants, water, photosynthesis, carbon diox-ide, sun’s energy

One possibleanswer is pro-vided at right, but don’t look at it until you try the concept mapyourself.


What Is a Concept Map?Have you ever tried to tell someone about abook or a chapter you’ve just read and foundthat you can remember only a few isolatedwords and ideas? Or maybe you’ve mem-orized facts for a test and then weeks laterdiscovered you’re not even sure what topicsthose facts covered.

In both cases, you may have understoodthe ideas or concepts by themselves but not

in relation to one another. If you could some-how link the ideas together, you would prob-ably understand them better and rememberthem longer. This is something a concept mapcan help you do. A concept map is a way tosee how ideas or concepts fit together. It canhelp you see the “big picture.”

Concept Mapping: A Way to Bring Ideas Together

blood

carries

arteries veins

The circulatory system

from the heart through

to the heart through

2

3

4

1

Plants

carry out

photosynthesis

carbondioxide

using

watersun'senergy

States of matter

include

water

such as

ice water vapor

liquid gassolid

such assuch as


AP

PE

ND

IXSI MeasurementThe International System of Units, or SI, isthe standard system of measurement used bymany scientists. Using the same standards ofmeasurement makes it easier for scientists tocommunicate with one another.

SI works by combining prefixes and baseunits. Each base unit can be used with dif-ferent prefixes to define smaller and largerquantities. The table below lists common SIprefixes.

SI Prefixes

Prefix Abbreviation Factor Example

kilo- k 1,000 kilogram, 1 kg = 1,000 ghecto- h 100 hectoliter, 1 hL = 100 Ldeka- da 10 dekameter, 1 dam = 10 m

1 meter, literdeci- d 0.1 decigram, 1 dg = 0.1 gcenti- c 0.01 centimeter, 1 cm = 0.01 mmilli- m 0.001 milliliter, 1 mL = 0.001 Lmicro- µ 0.000 001 micrometer, 1 µm = 0.000 001 m

SI Conversion Table

SI units From SI to English From English to SILengthkilometer (km) = 1,000 m 1 km = 0.621 mi 1 mi = 1.609 km

meter (m) = 100 cm 1 m = 3.281 ft 1 ft = 0.305 m

centimeter (cm) = 0.01 m 1 cm = 0.394 in. 1 in. = 2.540 cm

millimeter (mm) = 0.001 m 1 mm = 0.039 in.

micrometer (µm) = 0.000 001 m

nanometer (nm) = 0.000 000 001 m

Area

square kilometer (km2) = 100 hectares 1 km2 = 0.386 mi2 1 mi2 = 2.590 km2

hectare (ha) = 10,000 m2 1 ha = 2.471 acres 1 acre = 0.405 ha

square meter (m2) = 10,000 cm2 1 m2 = 10.765 ft2 1 ft2 = 0.093 m2

square centimeter (cm2) = 100 mm2 1 cm2 = 0.155 in.2 1 in.2 = 6.452 cm2

Volume

liter (L) = 1,000 mL = 1 dm3 1 L = 1.057 fl qt 1 fl qt = 0.946 L

milliliter (mL) = 0.001 L = 1 cm3 1 mL = 0.034 fl oz 1 fl oz = 29.575 mL

microliter (µL) = 0.000 001 L

Mass

kilogram (kg) = 1,000 g 1 kg = 2.205 lb 1 lb = 0.454 kg

gram (g) = 1,000 mg 1 g = 0.035 oz 1 oz = 28.349 g

milligram (mg) = 0.001 g

microgram (µg) = 0.000 001 g

729Appendix

Appendix730

AP

PE

ND

IXTemperature ScalesTemperature can be expressed using three dif-ferent scales: Fahrenheit, Celsius, and Kelvin.The SI unit for temperature is the kelvin (K).

Although 0 K is much colder than 0°C, achange of 1 K is equal to a change of 1°C.



37˚ 310

212˚

98.6˚

32˚

100˚

20˚

0˚

373

293

273

68˚

Water boilsKelvinCelsiusFahrenheit

Body temperature

Room temperature

Water freezes

Temperature Conversions Table

To convert

Celsius to Fahrenheit°C °F

Fahrenheit to Celsius°F °C

Celsius to Kelvin

°C K

Kelvin to CelsiusK °C

Use this equation:

°F 95 °C 32

°C 59 (°F 32)

K °C 273

°C K 273

Example

Convert 45°C to °F.

°F 95 45°C 32 113°F


°C 59 (68°F 32) 20°C

Convert 45°C to K.

K 45°C 273 318 K

Convert 32 K to °C.

°C 32 K 273 241°C

Appendix 731

AP

PE

ND

IXMeasuring Skills

Using a Graduated CylinderWhen using a graduated cylinder to measure vol-ume, keep the following procedures in mind:

Make sure the cylinder is on a flat, level surface.

Move your head so that your eye is level withthe surface of the liquid.

Read the mark closest to the liquid level. Onglass graduated cylinders, read the mark closest to the center of the curve in the liquid’s surface.

Using a Meterstick or Metric RulerWhen using a meterstick or metric ruler to measurelength, keep the following procedures in mind:

Place the ruler firmly against the object you aremeasuring.

Align one edge of the object exactly with thezero end of the ruler.

Look at the other edge of the object to seewhich of the marks on the ruler is closest to thatedge. Note: Each small slash between the centi-meters represents a millimeter, which is one-tenth of a centimeter.

Using a Triple-Beam BalanceWhen using a triple-beam balance to measure mass, keep the following procedures in mind:

Make sure the balance is on a level surface.

Place all of the countermasses at zero. Adjust the balancing knob until the pointer rests at zero.

Place the object you wish to measure on thepan. Caution: Do not place hot objects or chemicals directly on the balance pan.

Move the largest countermass along the beam tothe right until it is at the last notch that does nottip the balance. Follow the same procedure withthe next-largest countermass. Then move thesmallest countermass until the pointer rests atzero.

Add the readings from the three beams togetherto determine the mass of the object.

When determining the mass of crystals orpowders, use a piece of filter paper. First find the mass of the paper. Then add the crystals or powder to the paper and re-measure. The actual mass of the crystals orpowder is the total mass minus the mass ofthe paper. When finding the mass of liquids,first find the mass of the empty container.Then find the mass of the liquid and con-tainer together. The mass of the liquid is thetotal mass minus the mass of the container.


0 1 2 3 4 5 6 7123456 987 123456 987 123456 987 123456 987 123456 987 123456 987 123456 987 12345

2

3

4

1

2

3

1

2

3

5

6

1


Appendix732

AP

PE

ND

IXScientific MethodThe series of steps that scientists use to answer questions andsolve problems is often called the scientific method. The scientificmethod is not a rigid procedure. Scientists may use all of thesteps or just some of the steps of the scientific method. Theymay even repeat some of the steps. The goal of the scientificmethod is to come up with reliable answers and solutions.

Six Steps of the Scientific Method

1 Ask a Question Good questions come from careful observations. You make observations by using your senses to gather information. Sometimes you may use instruments,

such as microscopes and telescopes, to extend the range of yoursenses. As you observe the natural world, you will discover that youhave many more questions than answers. These questions drive thescientific method.

Questions beginning with what, why, how, and when are veryimportant in focusing an investigation, and they often lead to ahypothesis. (You will learn what a hypothesis is in the next step.)Here is an example of a question that could lead to further investigation.

Question: How does acid rain affect plant growth?

2 Form a Hypothesis After you come up with a question,you need to turn the question into a hypothesis. A hypoth-esis is a clear statement of what you expect the answer to

your question to be. Your hypothesis will represent your best “edu-cated guess” based on your observations and what you already know.A good hypothesis is testable. If observations and information cannotbe gathered or if an experiment cannot be designed to test yourhypothesis, it is untestable, and the investigation can go no further.

Here is a hypothesis that could be formed from the question,“How does acid rain affect plant growth?”

Hypothesis: Acid rain causes plants to grow more slowly.

Notice that the hypothesis provides some specifics that lead tomethods of testing. The hypothesis can also lead to predictions. Aprediction is what you think will be the outcome of your experimentor data collection. Predictions are usually stated in an “if . . . then”format. For example, if meat is kept at room temperature, then it willspoil faster than meat kept in the refrigerator. More than one predic-tion can be made for a single hypothesis. Here is a sample predictionfor the hypothesis that acid rain causes plants to grow more slowly.

Prediction: If a plant is watered with only acid rain (which has a pHof 4), then the plant will grow at half its normal rate.

Ask a Question

Form aHypothesis


CommunicateResults

Appendix 733

AP

PE

ND

IX

3 Test the Hypothesis After you have formed ahypothesis and made a prediction, you should testyour hypothesis. There are different ways to do this.

Perhaps the most familiar way is to conduct a controlledexperiment. A controlled experiment tests only one factor at a time. A controlled experiment has a control group andone or more experimental groups. All the factors for thecontrol and experimental groups are the same except forone factor, which is called the variable. By changing onlyone factor, you can see the results of just that one change.

Sometimes, the nature of an investigation makes a controlledexperiment impossible. For example, dinosaurs have been extinct formillions of years, and the Earth’s core is surrounded by thousands ofmeters of rock. It would be difficult, if not impossible, to conductcontrolled experiments on such things. Under such circumstances, ahypothesis may be tested by making detailed observations. Takingmeasurements is one way of making observations.

4 Analyze the Results After you have completed your experiments, made your observations, and collected your data, you must analyze all the information you have gathered.

Tables and graphs are often used in this step to organize the data.

5 Draw Conclusions Based on the analysis of your data, you should conclude

whether or not your results sup-port your hypothesis. If your hypothesis is supported, you (or others) might want to repeat the observations or experiments to verify your results. If your hypoth-esis is not supported by the data, you may have to check your pro-cedure for errors. You may even have to reject your hypothesis and make a new one. If you cannot draw a conclusion from your results, you may have to try the investigation again or carry out further observations or experiments.

6 Communicate Results After any scientific investigation, you should report your results. By doing a written

or oral report, you let others know what you have learned. They may want to repeat your investigation to see if they get the same results. Your report may even lead to another question, which in turn may lead to another investigation.

Analyzethe Results

Test theHypothesis

No

Yes

Draw Conclusions

Do they support your hypothesis?


Appendix734

AP

PE

ND

IXScientific Method in ActionThe scientific method is not a “straight line” of steps. It con-tains loops in which several steps may be repeated over andover again, while others may not be necessary. For example,sometimes scientists will find that testing one hypothesis raisesnew questions and new hypotheses to be tested. And some-times, testing the hypothesis leads directly to a conclusion.Furthermore, the steps in the scientific method are not alwaysused in the same order. Follow the steps in the diagram below,and see how many different directions the scientific methodcan take you.

Form a hypothesisAsk a question

Test thehypothesis

Make observations

Analyzethe results

Draw conclusions

Perform experiments

Communicateresults

Was process faulty?

Appendix 735

AP

PE

ND

IX

Circle GraphsA circle graph, or pie chart, shows how eachgroup of data relates to all of the data. Each partof the circle represents a category of the data.The entire circle represents all of the data. Forexample, a biologist studying a hardwood forestin Wisconsin found that there were five differ-ent types of trees. The data table at right sum-marizes the biologist’s findings.

Making Charts and Graphs

Now determine the size of the pie shapesthat make up the chart. Do this by multiply-ing each percentage by 360°. Remember thata circle contains 360°.

20% 360° = 72° 25% 360° = 90°10% 360° = 36° 40% 360° = 144°5% 360° = 18°

Then check that the sum of the percentagesis 100 and the sum of the degrees is 360.

20% + 25% + 10% + 40% + 5% = 100%72° + 90° + 36° + 144° + 18° = 360°

Use a compass to draw a circle and mark itscenter.

Then use a protractor to draw angles of 72°,90°, 36°, 144°, and 18° in the circle.

Finally, label each part of the graph, andchoose an appropriate title.


Wisconsin Hardwood Trees

Type of tree Numberfound

Oak 600Maple 750Beech 300

Birch 1,200

Hickory 150Total 3,000

4

2

3

5

6

1

How to Make a Circle GraphIn order to make a circle graph of this data,first find the percentage of each type of tree.To do this, divide the number of individualtrees by the total number of trees andmultiply by 100.

3,600000

otraekes 100 = 20%

37,50000

mtarepeles 100 = 25%

33,00000

betreecehs 100 = 10%

13,,200000

btriercehs 100 = 40%

135,0000

hictrkeoersy

100 = 5%

Oak

Maple

Beech

Birch

600

150

750

300

1,200

HickoryA Community of Wisconsin Hardwood Trees


Appendix736

AP

PE

ND

IXLine GraphsLine graphs are most often used to demonstrate continuouschange. For example, Mr. Smith’s science class analyzed thepopulation records for their hometown, Appleton, between1900 and 2000. Examine the data at left.

Because the year and the population change, they are thevariables. The population is determined by, or dependent on,the year. Therefore, the population is called the dependentvariable, and the year is called the independent variable. Eachset of data is called a data pair. To prepare a line graph, datapairs must first be organized in a table like the one at left.

How to Make a Line GraphPlace the independent variable along thehorizontal (x) axis. Place the dependentvariable along the vertical (y) axis.

Label the x-axis “Year” and the y-axis“Population.” Look at your largest andsmallest values for the population.Determine a scale for the y-axis that willprovide enough space to show thesevalues. You must use the same scale forthe entire length of the axis. Find anappropriate scale for the x-axis too.

Choose reasonable starting points for each axis.

Plot the data pairs as accurately aspossible.

Choose a title that accurately represents the data.

Year Population1900 1,8001920 2,5001940 3,2001960 3,9001980 4,6002000 5,300

Calculate the slope of the graph by dividingthe change in y by the change in x.

slope = cchh

aann

ggee

iinn

yx

slope = 3,150000

ypeeaorpsle

slope = 35 people per year

In this example, the population in Appletonincreased by a fixed amount each year. Thegraph of this data is a straight line. There-fore, the relationship is linear. When thegraph of a set of data is not a straight line,the relationship is nonlinear.

How to Determine SlopeSlope is the ratio of the change in the y-axisto the change in the x-axis, or “rise over run.”

Choose two points on the line graph. Forexample, the population of Appleton in 2000was 5,300 people. Therefore, you can definepoint a as (2000, 5,300). In 1900, the popu-lation was 1,800 people. Define point b as(1900, 1,800).

Find the change in the y-axis.(y at point a) (y at point b)5,300 people 1,800 people = 3,500 people

Find the change in the x-axis.(x at point a) (x at point b)2000 1900 100 years

4

2

3

5

1

4

2

3

1

Population of Appleton, 1900–2000

Year

Popu

lati

on

6,000

5,000

4,000

3,000

2,000

1,000

01900 1920 1940 1960 1980 2000

Population of Appleton,1900–2000

Appendix 737

AP

PE

ND

IXUsing Algebra to Determine Slope

The equation in step 4 may also be arrangedto be:

y kx

where y represents the change in the y-axis, k represents the slope, and x represents thechange in the x-axis.

slope cchhaannggee

iinn

yx

k yx

k x y

xx

kx y


Bar GraphsBar graphs are used to demonstratechange that is not continuous. Thesegraphs can be used to indicate trendswhen the data are taken over a longperiod of time. A meteorologist gatheredthe precipitation records at right forHartford, Connecticut, for April 1–15,1996, and used a bar graph to representthe data.

How to Make a Bar GraphUse an appropriate scale and a reasonable starting point for each axis.

Label the axes, and plot the data.

Choose a title that accurately represents the data.

2

3

1

Precipitation in Hartford, ConnecticutApril 1–15, 1996

Date Precipitation Date Precipitation(cm) (cm)

April 1April 2April 3April 4April 5April 6April 7April 8

0.51.250.00.00.00.00.01.75

April 9April 10April 11April 12April 13April 14April 15

0.250.01.00.00.250.06.50

April

Prec

ipit

atio

n (c

m)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

7.0

6.0

5.0

4.0

3.0

2.0

1.0

0

Precipitation in Hartford, Connecticut, April 1–15, 1996

Appendix738

AP

PE

ND

IXMath Refresher

AveragesAn average, or mean, simplifies a list of num-bers into a single number that approximatestheir value.

Example: Find the average of the following set of numbers: 5, 4, 7, and 8.

RatiosA ratio is a comparison between numbers, andit is usually written as a fraction.

Example: Find the ratio of thermometers tostudents if you have 36 thermometers and48 students in your class.

ProportionsA proportion is an equation that states thattwo ratios are equal.

31

142

To solve a proportion, first multiply across theequal sign. This is called cross-multiplication. Ifyou know three of the quantities in a propor-tion, you can use cross-multiplication to findthe fourth.

Example: Imagine that you are making a scale model of the solar system for your sci-ence project. The diameter of Jupiter is 11.2times the diameter of the Earth. If you areusing a plastic-foam ball with a diameter of 2 cm to represent the Earth, what diameterdoes the ball representing Jupiter need to be?

11

1.2 2

xcm

Step 1: Find the sum.

5 4 7 8 24

Step 2: Divide the sum by the amount of numbers inyour set. Because there are four numbers inthis example, divide the sum by 4.

244 6

The average, or mean, is 6.

Step 1: Make the ratio.

Step 2: Reduce the fraction to its simplest form.

34

68

34

68

1122

34

The ratio of thermometers to students is 3 to

4, or 34. The ratio may also be written in the

form 3:4.

Step 1: Cross-multiply.

11

1.2 2

x

11.2 2 x 1

Step 2: Multiply.

22.4 x 1

Step 3: Isolate the variable by dividing both sides by 1.

x 22

1.4

x 22.4 cm

You will need to use a ball with a diameter of 22.4 cm to represent Jupiter.

36 thermometers48 students


Science requires an understanding of many math concepts. Thefollowing pages will help you review some important math skills.

Appendix 739

AP

PE

ND

IX

PercentagesA percentage is a ratio of a given number to100.

Example: What is 85 percent of 40?

DecimalsTo add or subtract decimals, line up the digitsvertically so that the decimal points line up.Then add or subtract the columns from right toleft, carrying or borrowing numbers asnecessary.

Example: Add the following numbers:3.1415 and 2.96.

FractionsNumbers tell you how many; fractions tell youhow much of a whole.

Example: Your class has 24 plants. Yourteacher instructs you to put 5 in a shadyspot. What fraction does this represent?

Reducing FractionsIt is usually best to express a fraction in sim-plest form. This is called reducing a fraction.

Example: Reduce the fraction 34

05 to its

simplest form.

Step 1: Rewrite the percentage by moving the deci-mal point two places to the left.

.85

Step 2: Multiply the decimal by the number you arecalculating the percentage of.

0.85 40 = 34

85 percent of 40 is 34.

Step 1: Line up the digits vertically so that the deci-mal points line up.

3.1415 2.96

Step 2: Add the columns from right to left, carryingwhen necessary.

1 13.1415

2.966.1015

The sum is 6.1015.

Step 1: Write a fraction with the total number ofparts in the whole as the denominator.

2?4

Step 2: Write the number of parts of the whole beingrepresented as the numerator.

254

254 of the plants will be in the shade.

Step 1: Find the largest whole number that willdivide evenly into both the numerator anddenominator. This number is called thegreatest common factor (GCF).

factors of the numerator 30: 1, 2, 3, 5, 6, 10,15, 30

factors of the denominator 45: 1, 3, 5, 9, 15,45

Step 2: Divide both the numerator and the denomi-nator by the GCF, which in this case is 15.

34

05

34

05

1155

23

34

05 reduced to its simplest form is

23.


Appendix740

AP

PE

ND

IX

Adding and SubtractingTo add or subtract fractions that have thesame denominator, simply add or subtract thenumerators.

Examples:

35

15 ? and

34

14 ?

To add or subtract fractions that have differ-ent denominators, first find the least commondenominator (LCD).

Examples:

12

16 ? and

34

23 ?

Multiplying FractionsTo multiply fractions, multiply the numeratorsand the denominators together, and thenreduce the fraction to its simplest form.

Example:

59 1

70 ?

Dividing FractionsTo divide fractions, first rewrite the divisor (thenumber you divide by) upside down. This iscalled the reciprocal of the divisor. Then youcan multiply and reduce if necessary.

Example:

58

32 ?

Step 1: Add or subtract the numerators.

35

15

4x and

34

14

2x

Step 2: Write the sum or difference over the denominator.

35

15

45 and

34

14

24

Step 3: If necessary, reduce the fraction to its simplest form.

45 cannot be reduced, and

24 =

12.

Step 1: Write the equivalent fractions with acommon denominator.

36

16 ? and 1

92 1

82 ?

Step 2: Add or subtract.

36

16

46 and 1

92 1

82 1

12

Step 3: If necessary, reduce the fraction to itssimplest form.

46

23, and 1

12 cannot be reduced.

Step 1: Multiply the numerators and denominators.

59 1

70 9

5

170

39

50

Step 2: Reduce.

39

50

39

50

55 1

78

Step 1: Rewrite the divisor as its reciprocal.

32

23

Step 2: Multiply.

58

23

58

23

1204

Step 3: Reduce.

1204

1204

22 1

52


Fractions

Appendix 741

AP

PE

ND

IX

Scientific NotationScientific notation is a short way of represent-ing very large and very small numbers withoutwriting all of the place-holding zeros.

Example: Write 653,000,000 in scientificnotation.

AreaArea is the number of square units needed tocover the surface of an object.

Formulas:Area of a square side sideArea of a rectangle length widthArea of a triangle

12 base height

Examples: Find the areas.

VolumeVolume is the amount of space something occupies.

Formulas:Volume of a cube side side side

Volume of a prism area of base height

Examples:Find the volume of the solids.

Step 1: Write the number without the place-holdingzeros.

653

Step 2: Place the decimal point after the first digit.

6.53

Step 3: Find the exponent by counting the numberof places that you moved the decimal point.

6 .53000000

The decimal point was moved eight places tothe left. Therefore, the exponent of 10 ispositive 8. Remember, if the decimal pointhad moved to the right, the exponent wouldbe negative.

Step 4: Write the number in scientific notation.

6.53 108


SquareArea side sideArea 3 cm 3 cm Area 9 cm2

RectangleArea length widthArea 6 cm 3 cmArea 18 cm2

CubeVolume side side sideVolume 4 cm 4 cm 4 cmVolume 64 cm3

PrismVolume area of base heightVolume (area of triangle) height

Volume 12 3 cm 4 cm 5 cm

Volume 6 cm2 5 cm Volume 30 cm3

TriangleArea

12 base height

Area 12 3 cm 4 cm

Area 6 cm2

Appendix742

AP

PE

ND

IX

Atoms and ElementsEvery object in the universe is made up ofparticles of some kind of matter. Matter isanything that takes up space and has mass.All matter is made up of elements. An elementis a substance that cannot be separated intosimpler components by ordinary chemicalmeans. This is because each element consistsof only one kind of atom. An atom is thesmallest unit of an element that has all ofthe properties of that element.

Atomic StructureAtoms are made up of small particles calledsubatomic particles. The three major types ofsubatomic particles are electrons, protons, andneutrons. Electrons have a negative electriccharge, protons have a positive charge, andneutrons have no electric charge. The pro-tons and neutrons are packed close to oneanother to form the nucleus. The protons givethe nucleus a positive charge. Electrons aremost likely to be found in regions aroundthe nucleus called electron clouds. The nega-tively charged electrons are attracted to thepositively charged nucleus. An atom mayhave several energy levels in which electronsare located.

Atomic NumberTo help in the identification of elements,scientists have assigned an atomic number toeach kind of atom. The atomic number isthe number of protons in the atom. Atomswith the same number of protons are all thesame kind of element. In an uncharged, orelectrically neutral, atom there are an equalnumber of protons and electrons. Therefore,the atomic number equals the number ofelectrons in an uncharged atom. The num-ber of neutrons, however, can vary for agiven element. Atoms of the same elementthat have different numbers of neutrons arecalled isotopes.

Periodic Table of theElements In the periodic table, the elements are arrangedfrom left to right in order of increasing atomicnumber. Each element in the table is in aseparate box. An atom of each element hasone more electron and one more proton thanan atom of the element to its left. Each hori-zontal row of the table is called a period.Changes in chemical properties of elementsacross a period correspond to changes in theelectron arrangements of their atoms. Eachvertical column of the table, known as a group,lists elements with similar properties. The elements in a group have similar chemicalproperties because their atoms have the samenumber of electrons in their outer energylevel. For example, the elements helium,neon, argon, krypton, xenon, and radon allhave similar properties and are known as thenoble gases.


Physical Science Refresher

Electron clouds

Nucleus

Appendix 743

AP

PE

ND

IX

When two or more elements arejoined chemically, the resultingsubstance is called a compound.

A compound is a new substancewith properties different from those

of the elements that compose it. For exam-ple, water, H2O, is a compound formed whenhydrogen (H) and oxygen (O) combine. Thesmallest complete unit of a compound thathas the properties of that compound is calleda molecule. A chemical formula indicates theelements in a compound. It also indicates therelative number of atoms of each elementpresent. The chemical formula for water isH2O, which indicates that each water mol-ecule consists of two atoms of hydrogen andone atom of oxygen. The subscript numberis used after the symbol for anelement to indicate how manyatoms of that element are ina single molecule of the compound.

Acids, Bases, and pHAn ion is an atom or group of atoms thathas an electric charge because it has lost orgained one or more electrons. When an acid,such as hydrochloric acid, HCl, is mixed with water, it separates into ions. An acid is

a compound that produces hydrogen ions,H+, in water. The hydrogen ions then combinewith a water molecule to form a hydroniumion, H3O+. A base, on the other hand, is asubstance that produces hydroxide ions, OH,in water.

To determine whether a solution is acidicor basic, scientists use pH. The pH is a meas-ure of the hydronium ion concentration ina solution. The pH scale ranges from 0 to 14.The middle point, pH 7, is neutral, neitheracidic nor basic. Acids have a pH less than7; bases have a pH greater than 7. The lowerthe number is, the more acidic the solution.The higher the number is, the more basic thesolution.

Chemical Equations A chemical reaction occurs when a chemicalchange takes place. (In a chemical change,new substances with new properties areformed.) A chemical equation is a useful wayof describing a chemical reaction by meansof chemical formulas. The equation indicateswhat substances react and what the productsare. For example, when carbon and oxygencombine, they can form carbon dioxide. Theequation for the reaction is as follows: C O2 CO2.


Increasing acidity Increasing basicity

Lemonjuice

Softdrink

Humansaliva

Tap water

Acid rain Clean rain

Human stomach contents

Seawater

Detergents Householdammonia

Milk

1 2 3 4 5 6 7 8 9 10 11 12 13

Molecules and Compounds


Appendix744

AP

PE

ND

IX

140.1

232.0

140.9

231.0

144.2

238.0

(144.9)

(237.0)

150.4

244.1

6.9

23.0

39.1

85.5

132.9

(223.0)

9.0

24.3

40.1

87.6

137.3

(226.0)

45.0

88.9

138.9

(227.0)

47.9

91.2

178.5

(261.1)

50.9

92.9

180.9

(262.1)

52.0

95.9

183.8

(263.1)

54.9

(97.9)

186.2

(262.1)

55.8

101.1

190.2

(265)

58.9

102.9

192.2

(266)

1.0

Praseodymium

Rutherfordium

Molybdenum

Lithium

Sodium

Potassium

Rubidium

Cesium

Francium

Cerium

Thorium Protactinium

Neodymium

Uranium

Promethium

Neptunium

Samarium

Plutonium

Beryllium

Magnesium

Calcium

Strontium

Barium

Radium

Scandium

Yttrium

Lanthanum

Actinium

Titanium

Zirconium

Hafnium

Vanadium

Niobium

Tantalum

Dubnium

Chromium

Tungsten

Seaborgium

Manganese

Technetium

Rhenium

Bohrium

Iron

Ruthenium

Osmium

Hassium

Cobalt

Rhodium

Iridium

Meitnerium

Hydrogen

Li

V

Na

K

Rb

Cs

Fr

Be

Mg

Ca

Sr

Ba

Ra

Sc

Y

La

Ac

Ti

Zr

H f

Rf

Nb

Ta

Db

Cr

Mo

W

Sg

Mn

Re

Bh

IrOs

Ce

Th

Pr

Pa

Nd

U

Pm

Np

Sm

Pu

Fe

Ru

Hs

Co

Rh

Mt

H

Tc

3

11

19

37

55

87

58

90

59

91

60

92

61

93

62

94

4

12

20

38

56

88

21

39

57

89

22

40

72

104

23

41

73

105

24

42

74

106

25

43

75

107

26

44

76 77

108

27

45

109

1

Group 3 Group 4 Group 5 Group 6 Group 7 Group 8 Group 9

Group 1 Group 2

Period 1

Period 2

Period 3

Period 4

Period 5

Period 6

Period 7

Lanthanides

Actinides

Background

Metals

Metalloids

Nonmetals

Chemical symbol

Solid

Liquid

Gas

6

CCarbon

12.0

Periodic Tableof the ElementsEach square on the table includes anelement’s name, chemical symbol,atomic number, and atomic mass.

Atomic number

Chemical symbol

Element name

Atomic mass

The color of the chemicalsymbol indicates the physicalstate at room temperature.Carbon is a solid.

The background colorindicates the type ofelement. Carbon is anonmetal.

A column of el-ements is called a group or family.

A row of elements iscalled a period.

These elements are placed below thetable to allow the table to be narrower.

Appendix 745

AP

PE

ND

IX

152.0

(243.1)

157.3

(247.1)

158.9

(247.1)

162.5

(251.1)

164.9

(252.1)

167.3

(257.1)

168.9

(258.1)

173.0

(259.1)

175.0

(262.1)

58.7 63.5 65.4 69.7 72.6 74.9 79.0 79.9 83.8

27.0 28.1 31.0 32.1 35.5 39.9

10.8 12.0 14.0 16.0 19.0 20.2

4.0

106.4 107.9 112.4 114.8 118.7 121.8 127.6 126.9 131.3

195.1

(271) (272)

197.0 200.6 204.4 207.2 209.0 (209.0) (210.0) (222.0)

(277)

Europium

Americium

Gadolinium

Curium

Terbium

Berkelium

Dysprosium

Californium

Holmium

Einsteinium

Erbium

Fermium

Thulium

Mendelevium

Ytterbium

Nobelium

Lutetium

Lawrencium

Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton

Aluminum Silicon Phosphorus Sulfur Chlorine Argon

Boron Carbon Nitrogen Oxygen Fluorine Neon

Helium

Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon


Platinum Gold Mercury Thallium Lead Bismuth Polonium Astatine Radon

Ununbium

Eu

Am

Gd

Cm

Tb

Bk

Dy

Cf

Pd Ag Cd In Sn Sb Te I Xe

Pt

Uun Uuu

Au Hg Tl Pb Bi Po At Rn

Ho

Es

Er

Fm

Tm

Md

Yb

No

Lu

Lr

Ni Cu Zn Ga Ge As Se Br Kr

Al Si P S Cl Ar

B C N O F Ne

He

Uub

28 29 30 31 32 33 34 35 36

13 14 15 16 17 18

5 6 7 8 9 10

2

46 47 48 49 50 51 52 53 54

78 79 80 81 82 83 84 85 86

110 111

63

95

64

96

65

97

66

98

67

99

68

100

69

101

70

102

71

103

112

Group 13 Group 14 Group 15 Group 16 Group 17

Group 18

Group 10 Group 11 Group 12

A number in parentheses is the mass numberof the most stable isotope of that element.

The names and symbols of elements 110–112 aretemporary. They are based on the atomic number ofthe element. The official name and symbol will beapproved by an international committee of scientists.

This zigzag linereminds you wherethe metals, nonmetals,and metalloids are.

TOPIC: Periodic TableGO TO: go.hrw.comKEYWORD: HN0 Periodic

Visit the HRW Web site to see the most recent version of the periodic table.


Appendix746

AP

PE

ND

IX

Law of Conservation ofEnergy

The law of conservation of energy states that energy can be neither created nordestroyed.

The total amount of energy in a closedsystem is always the same. Energy can bechanged from one form to another, but allthe different forms of energy in a systemalways add up to the same total amount ofenergy, no matter how many energy conver-sions occur.

Law of Universal Gravitation

The law of universal gravitation states that all objects in the universe attract each otherby a force called gravity. The size of the force depends on the masses of the objectsand the distance between them.

The first part of the law explains why abowling ball is much harder to lift than atable-tennis ball. Because the bowling ball hasa much larger mass than the table-tennis ball,the amount of gravity between the Earth andthe bowling ball is greater than the amountof gravity between the Earth and the table-tennis ball.

The second part of the law explains whya satellite can remain in orbit around theEarth. The satellite is carefully placed at a dis-tance great enough to prevent the Earth’sgravity from immediately pulling it down butsmall enough to prevent it from completelyescaping the Earth’s gravity and wanderingoff into space.

Newton’s Laws of Motion

Newton’s first law of motion states that anobject at rest remains at rest and an object in motion remains in motion at constantspeed and in a straight line unless acted onby an unbalanced force.

The first part of the law explains why afootball will remain on a tee until it is kickedoff or until a gust of wind blows it off.

The second part of the law explains whya bike’s rider will continue moving forwardafter the bike tire runs into a crack in the side-walk and the bike comes to an abrupt stopuntil gravity and the sidewalk stop the rider.

Newton’s second law of motion states thatthe acceleration of an object depends on the mass of the object and the amount offorce applied.

The first part of the law explains why theacceleration of a 4 kg bowling ball will begreater than the acceleration of a 6 kg bowl-ing ball if the same force is applied to both.

The second part of the law explains whythe acceleration of a bowling ball will belarger if a larger force is applied to it.

The relationship of acceleration (a) tomass (m) and force (F) can be expressed math-ematically by the following equation:

acceleration mfo

arcses, or a m

F

This equation is often rearranged to the form:

force mass acceleration,or

F m a

Newton’s third law of motion states thatwhenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.

This law explains that a runner is able tomove forward because of the equal and oppo-site force the ground exerts on the runner’sfoot after each step.


Physical Science Laws and Principles

Appendix 747

AP

PE

ND

IX

Charles’s Law

Charles’s law states that for a fixed amount of gas at a constant pressure, the volume ofthe gas increases as its temperature increases. Likewise, the volume of the gasdecreases as its temperature decreases.

If a basketball that was inflated indoorsis left outside on a cold winter day, the airparticles inside of the ball will move moreslowly. They will hit the sides of the basket-ball less often and with less force. The ballwill get smaller as the volume of the airdecreases. If a basketball that was inflatedoutdoors on a cold winter day is broughtindoors, the air particles inside of the ballwill move more rapidly. They will hit the sidesof the basketball more often and with moreforce. The ball will get larger as the volumeof the air increases.

Boyle’s Law

Boyle’s law states that for a fixed amount ofgas at a constant temperature, the volume of a gas increases as its pressure decreases.Likewise, the volume of a gas decreases as its pressure increases.

This law explains why the pressure of thegas in a helium balloon decreases as the bal-loon rises from the Earth’s surface.

Pascal’s Principle

Pascal’s principle states that a change inpressure at any point in an enclosed fluid will be transmitted equally to all parts of that fluid.

When a mechanic uses a hydraulic jackto raise an automobile off the ground, he orshe increases the pressure on the fluid in thejack by pushing on the jack handle. The pres-sure is transmitted equally to all parts of thefluid-filled jacking system. The fluid pressesthe jack plate against the frame of the car,lifting the car off the ground.

Archimedes’ Principle

Archimedes’ principle states that the buoy-ant force on an object in a fluid is equal tothe weight of the volume of fluid that theobject displaces.

A person floating in a swimming pool dis-places 20 L of water. The weight of that vol-ume of water is about 200 N. Therefore, thebuoyant force on the person is 200 N.


Law of Reflection

The law of reflection states that the angle ofincidence is equal to the angle of reflection. This law explains why light reflects off of a surface at the same angle it strikes the surface.

The beam oflight travelingtoward the mir-ror is called theincident beam.

The angle between theincident beam and thenormal is called theangle of incidence.

A line perpen-dicular to themirror’s surfaceis called thenormal. The beam of light

reflected off themirror is called thereflected beam.

The angle between thereflected beam andthe normal is calledthe angle of reflection.

Appendix748

AP

PE

ND

IXBernoulli’s Principle

Bernoulli’s principle states that as the speedof a moving fluid increases, its pressuredecreases.

Bernoulli’s principle explains how a winggives lift to an airplane or even how a Frisbee®

can fly through the air. Because of the shapeof the Frisbee, the air moving over the topof the Frisbee must travel farther than the airbelow the Frisbee in the same amount of time.In other words, the air above the Frisbee is

moving faster than the air below it. Thisfaster-moving air above the Frisbee exerts lesspressure than the slower-moving air below it.The resulting increased pressurebelow exerts an upwardforce, pushing theFrisbee up.


Useful Equations

Average speed

Average speed = tottoatladlistitman

ece

Example: A bicycle messenger traveled adistance of 136 km in 8 hours. What was the messenger’s average speed?

13

86

hkm = 17 km/h

The messenger’s average speed was 17 km/h.

Average acceleration

Average =acceleration

Example: Calculate the average accelerationof an Olympic 100 m dash sprinter whoreaches a velocity of 20 m/s south at thefinish line. The race was in a straight line and lasted 10 s.

20 m/

1s0

s0 m/s

= 2 m/s/s

The sprinter’s average acceleration is 2 m/s/s south.

final velocity starting velocitytime it takes to change velocity

Net force

Forces in the Same Direction

When forces are in the same direction, add theforces together to determine the net force.

Example: Calculate the net force on a stalledcar that is being pushed by two people. Oneperson is pushing with a force of 13 N north-west and the other person is pushing with aforce of 8 N in the same direction.

13 N + 8 N = 21 N

The net force is 21 N northwest.

Forces in Opposite Directions

When forces are in opposite directions, subtractthe smaller force from the larger force to deter-mine the net force.

Example: Calculate the net force on a ropethat is being pulled on each end. One personis pulling on one end of the rope with a forceof 12 N south. Another person is pulling onthe opposite end of the rope with a force of 7 N north.

12 N – 7 N = 5 N

The net force is 5 N south.


Work

Work is done by exerting a force through a dis-tance. Work has units of joules (J), which areequivalent to Newton-meters.

W = F d

Example: Calculate the amount of work done by a man who lifts a 100 N toddler 1.5 m off the floor.

W = 100 N 1.5 m = 150 N•m = 150 J

The man did 150 J of work.

Power

Power is the rate at which work is done. Poweris measured in watts (W), which are equivalentto joules per second.

P = Wt

Example: Calculate the power of aweightlifter who raises a 300 N barbell 2.1 m off the floor in 1.25 s.

W = 300 N 2.1 m = 630 N•m = 630 J

P = 16.3205

Js = 504 J/s = 504 W

The weightlifter has 504 W of power.

Pressure

Pressure is the force exerted over a given area.The SI unit for pressure is the pascal, which isabbreviated Pa.

Pressure = faorrecae

Example: Calculate the pressure of the air in a soccer ball if the air exerts a force of 10 N over an area of 0.5 m2.

Pressure = 01.50

mN

2 = 20 N/m2 = 20 Pa

The pressure of the air inside of the soccerball is 20 Pa.

Appendix 749

AP

PE

ND

IX

Density

Density = vom

luas

mse

Example: Calculate the density of a spongewith a mass of 10 g and a volume of 40 mL.

4100mgL = 0.25 g/mL

The density of the sponge is 0.25 g/mL.

Concentration

Concentration =

Example: Calculate the concentration of asolution in which 10 g of sugar is dissolvedin 125 mL of water.

12150

mg

Lof

osfuwgaatrer = 0.08 g/mL

The concentration of this solution is 0.08 g/mL.

mass of solutevolume of solvent

Glossary750

GL

OS

SA

RY A

absolute zero the lowest possible temperature (0 K, –273°C) (249)

absorption the transfer of energy carried by lightwaves to particles of matter (576)

acceleration (ak SEL uhr AY shuhn) the rate atwhich velocity changes; an object accelerates if itsspeed changes, if its direction changes, or if bothits speed and its direction change (112)

acid any compound that increases the number ofhydrogen ions when dissolved in water and whosesolution tastes sour and can change the color ofcertain compounds; acids turn blue litmus red,react with metals to produce hydrogen gas, andreact with limestone or baking soda to producecarbon dioxide gas (377)

activation energy the minimum amount of energyneeded for substances to react (362)

active solar heating a solar-heating system con-sisting of solar collectors and a network of pipesthat distributes energy from the sun throughout abuilding (265)

alkali (AL kuh LIE) metals the elements in Group1 of the periodic table; they are the most reactivemetals; their atoms have one electron in theirouter level (310)

alkaline-earth metals the elements in Group 2 ofthe periodic table; they are reactive metals but areless reactive than alkali metals; their atoms havetwo electrons in their outer level (311)

alloys solid solutions of metals or nonmetals dis-solved in metals (93)

alpha decay the release of an alpha particle froma nucleus (399)

alpha particle a type of nuclear radiation consist-ing of two protons and two neutrons emitted bythe nucleus of a radioactive atom; identical to thenucleus of a helium atom (399)

alternating current (AC) electric current in whichthe charges continually switch from flowing in onedirection to flowing in the reverse direction (434)

amplitude the maximum distance a wave vibratesfrom its rest position (516, 543)

analog (AN uh LAHG) signal a signal whose prop-erties, such as amplitude and frequency, canchange continuously according to changes in theoriginal information (489)

Archimedes’ (ahr kuh MEE deez) principle the prin-ciple that states that the buoyant force on an objectin a fluid is an upward force equal to the weight ofthe volume of fluid that the object displaces (168)

area a measure of how much surface an objecthas (26)

atmospheric pressure the pressure caused by theweight of the atmosphere (163)

atom the smallest particle into which an element canbe divided and still be the same substance (280)

atomic mass the weighted average of the massesof all the naturally occurring isotopes of anelement (292)

atomic mass unit (amu) the SI unit used toexpress the masses of particles in atoms (288)

atomic number the number of protons in thenucleus of an atom (290)

average speed the overall rate at which an objectmoves; average speed can be calculated by divid-ing total distance by total time (109)

Bbalanced forces forces on an object that causethe net force to be zero; balanced forces do notcause a change in motion or acceleration (118)

base any compound that increases the number of hydroxide ions when dissolved in water andwhose solution tastes bitter, feels slippery, and canchange the color of certain compounds; bases turnred litmus blue (379)

battery a device that is made of several cells andthat produces an electric current by convertingchemical energy into electrical energy (430)

Bernoulli’s (buhr NOO leez) principle the princi-ple that states that as the speed of a moving fluidincreases, its pressure decreases (173)

beta decay the release of a beta particle from anucleus (400)

beta particle an electron or positron emitted bythe nucleus of a radioactive atom (400)

bimetallic (BIE muh TAL ik) strip a strip made bystacking two different metals in a long thin strip;because the different metals expand at differentrates, a bimetallic strip can coil and uncoil withchanges in temperature; bimetallic strips are usedin devices such as thermostats (250)

binary (BIE neh ree) two; binary numbers containonly the digits 1 and 0 (490)


Glossary

Glossary 751

GL

OS

SA

RY

biochemicals organic compounds made by livingthings (384)

biomass organic matter, such as plants, wood, andwaste, that contains stored energy (236)

bit the name for each of the digits in a binarynumber (497)

block and tackle a fixed pulley and a movablepulley used together; it can have a large mechani-cal advantage if several pulleys are used (204)

boiling vaporization that occurs throughout aliquid (70)

boiling point the temperature at which a liquidboils and becomes a gas (70)

Boyle’s law the law that states that for a fixedamount of gas at a constant temperature, the volumeof a gas increases as its pressure decreases (65)

buoyant force the upward force that fluids exert on allmatter; buoyant force opposes gravitational force (168)

byte a unit in which computers store and processinformation; equal to eight bits (497)

Ccalorie the amount of energy needed to changethe temperature of 0.001 kg of water by 1°C; 1 calorie is equivalent to 4.184 J (258)

calorimeter (KAL uh RIM uht uhr) a device usedto determine the specific heat capacity of a sub-stance (258)

carbohydrates biochemicals composed of one ormore simple sugars bonded together that are usedas a source of energy and for energy storage (384)

catalyst (KAT uh LIST) a substance that speeds up areaction without being permanently changed (365)

cathode-ray tube (CRT) a special vacuum tube inwhich a beam of electrons is projected onto ascreen (493)

cell a device that produces an electric current by con-verting chemical energy into electrical energy (430)

central processing unit (CPU) the physical area inwhich a computer performs tasks (496)

centripetal (sen TRIP uht uhl) acceleration theacceleration that occurs in circular motion; an objecttraveling in a circle is constantly changing directions,so acceleration occurs continuously (114)

change of state the conversion of a substancefrom one physical form to another (68, 261)

characteristic property a property of a substancethat is always the same whether the sampleobserved is large or small (48)

Charles’s law the law that states that for a fixedamount of gas at a constant pressure, the volumeof a gas increases as its temperature increases (66)

chemical bond a force of attraction that holds twoatoms together (328)

chemical bonding the joining of atoms to formnew substances (328)

chemical change a change that occurs when oneor more substances are changed into entirely newsubstances with different properties; cannot bereversed using physical means (49, 262)

chemical energy the energy of a compound thatchanges as its atoms are rearranged to form anew compound; chemical energy is a form ofpotential energy (218)

chemical equation a shorthand description of achemical reaction using chemical formulas andsymbols (354)

chemical formula a shorthand notation for a com-pound or a diatomic element using chemical sym-bols and numbers (352)

chemical property a property of matter thatdescribes a substance based on its ability to changeinto a new substance with different properties (47)

chemical reaction the process by which one ormore substances undergo change to produce oneor more different substances (350)

circuit a complete, closed path through whichelectric charges flow (440)

circuit board a collection of hundreds of tiny cir-cuits that supply electric current to the variousparts of an electronic device (482)

coefficient (KOH uh FISH uhnt) a number placedin front of a chemical symbol or formula; used tobalance a chemical equation (356)

colloid (KAWL OYD) a mixture in which the parti-cles are dispersed throughout but are not heavyenough to settle out (97)

combustion the burning of fuel; specifically, theprocess in which fuel combines with oxygen in achemical change that produces thermal energy (266)

compound a pure substance composed of two ormore elements that are chemically combined (86)

compound machine a machine that is made oftwo or more simple machines (204)

compression a region of higher density or pres-sure in a wave (514, 534)

computer an electronic device that performs tasksby processing and storing information (494)


Glossary752

GL

OS

SA

RY

concave lens a lens that is thinner in the middlethan at the edges (604)

concave mirror a mirror that is curved inward likethe inside of a spoon (600)

concentration a measure of the amount of solutedissolved in a solvent (94, 364)

condensation the change of state from a gas to aliquid (71)

condensation point the temperature at which agas becomes a liquid (71)

conduction (electrical) a method of charging anobject that occurs when electrons are transferredfrom one object to another by direct contact (425)

conduction (thermal) the transfer of thermalenergy from one substance to another throughdirect contact; conduction can also occur within asubstance (253)

conductor (electrical) a material in which chargescan move easily (427)

conductor (thermal) a substance that conductsthermal energy well (254)

constructive interference interference that resultsin a wave that has a greater amplitude than thatof the individual waves (523, 548, 579)

convection the transfer of thermal energy by themovement of a liquid or a gas (254)

convection current the circular motion of liquidsor gases due to density differences that result fromtemperature differences (254)

convex lens a lens that is thicker in the middlethan at the edges (603)

convex mirror a mirror that is curved outward likethe back of a spoon (602)

cornea a transparent membrane that protects theeye and refracts light (605)

covalent (KOH VAY luhnt) bond the force of attrac-tion between the nuclei of atoms and the elec-trons shared by the atoms (336)

covalent compounds compounds that are com-posed of elements that are covalently bonded;these compounds are composed of independentmolecules, tend to have low melting and boilingpoints, do not usually dissolve in water, and formsolutions that do not conduct an electric currentwhen they do dissolve (375)

crest the highest point of a transverse wave (513)

crystal lattice (LAT is) a repeating three-dimensional pattern of ions (335)

current a continuous flow of charge caused by themotion of electrons; the rate at which charge passesa given point; expressed in amperes (A) (433)

Ddata any pieces of information acquired throughexperimentation (16)

decibel (dB) the most common unit used toexpress loudness (543)

decomposition reaction a reaction in which asingle compound breaks down to form two ormore simpler substances (359)

density the amount of matter in a given space;mass per unit volume (27, 44, 165)

destructive interference interference that resultsin a wave that has a smaller amplitude than thatof the individual waves (523, 548, 579)

diffraction the bending of waves around a barrieror through an opening (521, 551, 579)

digital signal a series of electrical pulses that rep-resents the digits of binary numbers (490)

diode (DIE OHD) an electronic component thatallows electric current in only one direction (484)

direct current (DC) electric current in which thecharges always flow in the same direction (434)

doping (DOHP eeng) the process of replacing afew atoms of a semiconductor with a few atomsof another substance that have a different numberof valence electrons (483)

Doppler effect the apparent change in the frequencyof a sound caused by the motion of either the listeneror the source of the sound (refers to sound only)(542)

double-replacement reaction a reaction in whichions in two compounds switch places (360)

drag the force that opposes or restricts motion ina fluid; drag opposes thrust (176)

ductility (duhk TIL uh tee) the ability of a sub-stance to be drawn or pulled into a wire (44, 340)

Eecho a reflected sound wave (520, 545)

echolocation the process of using reflected soundwaves to find objects (546)

electrical energy the energy of electric charges(219, 430)

electric discharge the loss of static electricity ascharges move off an object (428)


Glossary 753

GL

OS

SA

RY

electric field the region around a charged particlethat can exert a force on another charged particle(423)

electric force the force between charged objects(423)

electric motor a device that changes electricalenergy into kinetic energy (466)

electric power the rate at which electrical energyis used to do work; expressed in watts (W) (437)

electrode the part of a cell through which chargesenter or exit (430)

electrolyte in a cell, a mixture of chemicals thatcarries an electric current (430)

electromagnet a magnet that consists of a sole-noid wrapped around an iron core (464)

electromagnetic induction the process by whichan electric current is produced by a changing mag-netic field (469)

electromagnetic spectrum the entire range ofelectromagnetic waves (567)

electromagnetic wave a wave that can travelthrough space or matter and consists of changingelectric and magnetic fields (492, 512, 564)

electromagnetism the interaction between elec-tricity and magnetism (463)

electron clouds the regions inside an atom whereelectrons are likely to be found (286)

electrons the negatively charged particles found inall atoms; electrons are involved in the formationof chemical bonds (283)

element a pure substance that cannot be sepa-rated or broken down into simpler substances byphysical or chemical means (82)

endothermic the term used to describe a physicalor a chemical change in which energy is absorbed(69, 362)

energy the ability to do work (214)

energy conversion a change from one form ofenergy into another (222)

energy efficiency (e FISH uhn see) a comparison ofthe amount of energy before a conversion and theamount of useful energy after a conversion (228)

energy resource a natural resource that can beconverted by humans into other forms of energyin order to do useful work (232)

evaporation (ee VAP uh RAY shuhn) vaporizationthat occurs at the surface of a liquid below itsboiling point (70)

exothermic the term used to describe a physicalor a chemical change in which energy is releasedor removed (69, 361)

external combustion engine a heat engine thatburns fuel outside the engine, such as a steamengine (266)

Ffiber optics the use of optical fibers (thin, flexibleglass wires) to transmit light over long distances (612)

fixed pulley a pulley that is attached to somethingthat does not move; fixed pulleys change the direc-tion of a force but do not increase the force (203)

fluid any material that can flow and that takes theshape of its container (162)

fluorescent light visible light emitted by a phos-phor particle when it absorbs energy such as ultra-violet light (596)

focal length the distance between a mirror or lensand its focal point (600)

focal point the point on the axis of a mirror orlens through which all incident parallel light raysare focused (600)

force a push or a pull; all forces have both sizeand direction (115)

fossil fuels nonrenewable energy resources thatform in the Earth’s crust over millions of years fromthe buried remains of once-living organisms (232)

free fall the condition an object is in when gravityis the only force acting on it (141)

freezing the change of state from a liquid to asolid (69)

freezing point the temperature at which a liquidchanges into a solid (69)

frequency the number of waves produced in agiven amount of time (518, 540)

friction a force that opposes motion between twosurfaces that are touching (119, 229)

fulcrum the fixed point about which a lever pivots(198)

fundamental the lowest resonant frequency (550)

Ggamma decay the release of gamma rays from anucleus (400)

gamma rays EM waves with very high energy andno mass or charge; they are emitted by thenucleus of a radioactive atom (400, 574)


Glossary754

GL

OS

SA

RY

gas the state in which matter changes in bothshape and volume (63)

generator a device that uses electromagneticinduction to convert kinetic energy into electricalenergy (470)

geothermal energy energy resulting from theheating of the Earth’s crust (236)

gravitational potential energy energy due to anobject’s position above the Earth’s surface (216)

gravity a force of attraction between objects thatis due to their masses (39, 125)

greenhouse effect the natural heating process ofa planet, such as the Earth, by which gases in theatmosphere trap thermal energy (255)

group a column of elements on the periodic table(309)

Hhalf-life the amount of time it takes for one-half ofthe nuclei of a radioactive isotope to decay (404)

halogens the elements in Group 17 of the periodictable; they are very reactive nonmetals, and theiratoms have seven electrons in their outer level (316)

hardware the parts or equipment that make up acomputer (496)

heat the transfer of energy between objects thatare at different temperatures; energy is alwaystransferred from higher-temperature objects tolower-temperature objects until thermal equilib-rium is reached (251); also the amount of energythat is transferred between objects that are at dif-ferent temperatures (257)

heat engine a machine that uses heat to do work(266)

hertz (Hz) the unit used to express frequency; onehertz is one cycle per second (518, 540)

heterogeneous (HET uhr OH JEE nee uhs) mixturea combination of substances in which differentcomponents are easily observed (96)

hologram a piece of film on which an interferencepattern produces a three-dimensional image of anobject (611)

homogeneous (HOH moh JEE nee uhs) mixture acombination of substances in which the appear-ance and properties are the same throughout (92)

hydraulic (hie DRAW lik) device a device thatuses liquids to transmit pressure from one point toanother (167)

hydrocarbons organic compounds that are com-posed of only carbon and hydrogen (388)

hypothesis a possible explanation or answer to aquestion (14)

Iideal machine a machine that has 100 percentmechanical efficiency (197)

illuminated the term describing visible objectsthat are not a light source (594)

incandescent light light produced by hot objects(595)

inclined plane a simple machine that is a straight,slanted surface; a ramp (200)

induction a method of charging an object thatoccurs when charges in an uncharged object arerearranged without direct contact with a chargedobject (425)

inertia the tendency of all objects to resist anychange in motion (42, 147)

infrared waves EM waves that are betweenmicrowaves and visible light in the electromag-netic spectrum (571)

infrasonic the term describing sounds with fre-quencies lower than 20 Hz (541)

inhibitor a substance that slows down or stops achemical reaction (365)

inner ear the part of the ear where vibrations cre-ated by sound are changed into electrical signalsfor the brain to interpret (537)

input the information given to a computer (494)

input device a piece of hardware that feeds infor-mation to the computer (496)

input force the force applied to a machine (193)

insulation a substance that reduces the transfer ofthermal energy (264)

insulator (electrical) a material in which chargescannot easily move (427)

insulator (thermal) a substance that does notconduct thermal energy well (254)

integrated (IN tuh GRAYT ed) circuit an entire circuitcontaining many transistors and other electroniccomponents formed on a single silicon chip (486)

interference a wave interaction that occurs when twoor more waves overlap (522, 548, 579)

internal combustion engine a heat engine thatburns fuel inside the engine; for example, an auto-mobile engine (267)


Glossary 755

GL

OS

SA

RY

Internet a huge computer network consisting ofmillions of computers that can all share informa-tion with one another (499)

ionic (ie AHN ik) bond the force of attractionbetween oppositely charged ions (332)

ionic compounds compounds that contain ionicbonds; composed of ions arranged in a crystal lat-tice, they tend to have high melting and boilingpoints, are solid at room temperature, and dissolvein water to form solutions that conduct an electriccurrent (374)

ions charged particles that form during chemicalchanges when one or more valence electronstransfer from one atom to another (332)

iris the colored part of the eye (605)

isotopes atoms that have the same number ofprotons but have different numbers of neutrons(290, 400)

Jjoule (J) the unit used to express work and energy;equivalent to the newton-meter (N•m) (190)

Kkilocalorie the unit of energy equal to 1,000 calories;the kilocalorie can also be referred to as the Calorie,which is the unit of energy listed on food labels (258)

kinetic (ki NET ik) energy the energy of motion;kinetic energy depends on speed and mass (215)

Llaser a device that produces intense light of onlyone wavelength and color (609)

law a summary of many experimental results andobservations; a law tells how things work (19)

law of conservation of energy the law that statesthat energy is neither created nor destroyed (230,362)

law of conservation of mass the law that statesthat mass is neither created nor destroyed in ordi-nary chemical and physical changes (357)

law of electric charges the law that states that likecharges repel and opposite charges attract (423)

law of reflection the law that states that theangle of incidence is equal to the angle ofreflection (575)

law of universal gravitation the law that statesthat all objects in the universe attract each otherthrough gravitational force; the size of the forcedepends on the masses of the objects and thedistance between them (126)

lens a curved, transparent object that forms an imageby refracting light (603); also the part of the eye thatrefracts light to focus an image on the retina (605)

lever a simple machine consisting of a bar thatpivots at a fixed point, called a fulcrum; there arethree classes of levers, based on where the inputforce, output force, and fulcrum are placed in rela-tion to the load: first class levers, second classlevers, and third class levers (198)

lift an upward force on an object (such as a wing)that opposes the downward pull of gravity; differ-ences in pressure above and below the objectcontribute to lift (174)

light energy the energy produced by the vibra-tions of electrically charged particles (220)

lipids biochemicals that do not dissolve in water;their functions include storing energy and makingup cell membranes; waxes, fats, and oils (385)

liquid the state in which matter takes the shapeof its container and has a definite volume (62)

load a device that uses electrical energy to dowork (440)

longitudinal wave a wave in which the particlesof the medium vibrate back and forth along thepath that the wave travels (514)

loudness how loud or soft a sound is perceived tobe (542)

lubricant (LOO bri kuhnt) a substance applied tosurfaces to reduce the friction between them (123)

luminous the term describing objects that producevisible light (594)

Mmachine a device that helps make work easier bychanging the size or direction (or both) of a force(192)

magnet any material that attracts iron or materialscontaining iron (454)

magnetic field the region around a magnet inwhich magnetic forces can act (456)

magnetic force the force of repulsion or attractionbetween the poles of magnets (455)

malleability (MAL ee uh BIL uh tee) the ability of a substance to be pounded into thin sheets (44, 340)


Glossary756

GL

OS

SA

RY

mass the amount of matter that something ismade of (26, 38, 129)

mass number the sum of the protons and neu-trons in an atom (291, 399)

matter anything that has volume and mass (7, 36)

mechanical advantage a number that tells howmany times a machine multiplies force; can becalculated by dividing the output force by theinput force (196)

mechanical efficiency (e FISH uhn see) a com-parison—expressed as a percentage—of amachine’s work output with the work input; canbe calculated by dividing work output by workinput and then multiplying by 100 (197)

mechanical energy the total energy of motionand position of an object (217)

medium a substance through which a wave cantravel (511, 536)

melting the change of state from a solid to aliquid (69)

melting point the temperature at which a sub-stance changes from a solid to a liquid (69)

memory the location where a computer storesinformation (494)

meniscus (muh NIS kuhs) the curve at a liquid’ssurface by which you measure the volume of theliquid (37)

metallic bond the force of attraction between apositively charged metal ion and the electrons in a metal (339)

metalloids elements that have properties of bothmetals and nonmetals; sometimes referred to assemiconductors (85)

metals elements that are shiny and are good con-ductors of thermal energy and electric current;most metals are malleable and ductile (85)

meter (m) the basic unit of length in the SIsystem (25)

microprocessor an integrated circuit that containsmany of a computer’s capabilities on a single sili-con chip (495)

microwaves EM waves that are between radiowaves and infrared waves in the electromagneticspectrum (570)

middle ear the part of the ear where the ampli-tude of sound vibrations is increased (537)

mixture a combination of two or more substancesthat are not chemically combined (90)

model a representation of an object or system(20, 283)

modem a piece of computer hardware that allowscomputers to communicate over telephone lines(497)

molecule (MAHL i KYOOL) a neutral group ofatoms held together by covalent bonds (336)

momentum a property of a moving object thatdepends on the object’s mass and velocity (152)

motion an object’s change in position over timewhen compared with a reference point (108)

movable pulley a pulley attached to the objectbeing moved; movable pulleys increase force (203)

Nnegative acceleration acceleration in which veloc-ity decreases; also called deceleration (113)

neon light light emitted by atoms of certain gases,such as neon, when they absorb and then releaseenergy (596)

net force the force that results from combining allthe forces exerted on an object (116)

neutrons the particles of the nucleus that have nocharge (288)

newton (N) the SI unit of force (41, 115)

noble gases the unreactive elements in Group 18of the periodic table; their atoms have eight elec-trons in their outer level (except for helium, whichhas two electrons) (316)

noise any undesired sound, especially nonmusicalsound, that includes a random mix of pitches (555)

nonmetals elements that are dull and are poor con-ductors of thermal energy and electric current (85)

nonrenewable resource a natural resource thatcannot be replaced or that can be replaced onlyover thousands or millions of years (232)

nuclear (NOO klee uhr) chain reaction a continu-ous series of nuclear fission reactions (407)

nuclear energy the form of energy associated withchanges in the nucleus of an atom (221)

nuclear fission the process in which a largenucleus splits into two smaller nuclei (235, 406)

nuclear fusion the process in which two or morenuclei with small masses join together, or fuse, toform a larger, more massive nucleus (410)


Glossary 757

GL

OS

SA

RY

nuclear radiation high-energy particles and raysthat are emitted by the nuclei of some atoms;alpha particles, beta particles, and gamma rays aretypes of nuclear radiation (398)

nucleic acids biochemicals that store informationand help to build proteins and other nucleic acids;made up of subunits called nucleotides (387)

nucleus (NOO klee uhs) the tiny, extremely dense,positively charged region in the center of an atom;made up of protons and neutrons (285)

Oobservation any use of the senses to gatherinformation (12)

Ohm’s law the law that states the relationship be-tween current (I), voltage (V ), and resistance (R);

expressed by the equation I = RV

(437)

opaque the term describing matter that does nottransmit any light (582)

optical axis a straight line drawn outward fromthe center of a mirror or lens (600)

organic compounds covalent compounds com-posed of carbon-based molecules (383)

oscilloscope (uh SIL uh SKOHP) a device used tograph representations of sound waves (544)

outer ear the part of the ear that acts as a funnelto direct sound waves into the middle ear (537)

output the result of processing that is the finalresult or the proof of the task performed by acomputer (494)

output device a piece of hardware on which a com-puter shows the results of performing a task (497)

output force the force applied by a machine (193)

overtones resonant frequencies that are higherthan the fundamental (550)

Pparallel circuit a circuit in which different loadsare on separate branches (443)

pascal (Pa) the SI unit of pressure; equal to theforce of 1 N exerted over an area of one squaremeter (162)

Pascal’s principle the principle that states that achange in pressure at any point in an enclosed fluidis transmitted equally to all parts of that fluid (167)

passive solar heating a solar-heating system thatrelies on thick walls and large windows to useenergy from the sun as a means of heating (265)

period a horizontal row of elements on the peri-odic table (309)

periodic having a regular, repeating pattern (302)

periodic law the law that states that the chemicaland physical properties of elements are periodicfunctions of their atomic numbers (303)

perpendicular at right angles (513, 564)

perpetual (puhr PECH oo uhl) motion machine amachine that runs forever without any additionalenergy input; perpetual motion machines areimpossible to create (231)

pH a measure of hydronium ion concentration in asolution; a pH of 7 is neutral; a pH less than 7 isacidic; a pH greater than 7 is basic (380)

photocell the part of a solar panel that convertslight into electrical energy (432)

photon a tiny “packet” of energy that is releasedby an electron that moves to a lower energy levelin an atom (565)

physical change a change that affects one ormore physical properties of a substance; manyphysical changes are easy to undo (48, 261)

physical property a property of matter that can beobserved or measured without changing the iden-tity of the matter (43)

physical science the study of matter and energy (7)

pigment a material that gives a substance itscolor by absorbing some colors of light andreflecting others (584)

pitch how high or low a sound is perceived to be(540)

plane mirror a mirror with a flat surface (599)

plasma the state of matter that does not have adefinite shape or volume and whose particleshave broken apart; plasma is composed of elec-trons and positively charged ions (67)

polarized light consists of light waves that vibratein only one plane (one direction) (612)

poles the parts of a magnet where the magneticeffects are strongest (454)

positive acceleration acceleration in which veloc-ity increases (113)

positron a beta particle with a charge of 1+ and amass of almost 0 (400)

potential difference energy per unit charge; specifi-cally, the difference in energy per unit charge as acharge moves between two points in an electric cir-cuit (same as voltage); expressed in volts (V) (431)


Glossary758

GL

OS

SA

RY

potential energy the energy of position or shape(216)

power the rate at which work is done (191)

pressure the amount of force exerted on a givenarea; expressed in pascals (Pa) (64, 162)

primary colors of light red, blue, and green; thesecolors of light can be combined in different ratiosto produce all colors of light (584)

primary pigments yellow, cyan, and magenta;these pigments can be combined to produce anyother pigment (585)

products the substances formed from a chemicalreaction (354)

projectile (proh JEK tuhl) motion the curved pathan object follows when thrown or propelled nearthe surface of the Earth (143)

proteins biochemicals that are composed ofamino acids; their functions include regulatingchemical activities, transporting and storing materi-als, and providing structural support (386)

protons the positively charged particles of thenucleus; the number of protons in a nucleus is theatomic number that determines the identity of anelement (288)

pulley a simple machine consisting of a groovedwheel that holds a rope or a cable (203)

pupil the opening to the inside of the eye (605)

pure substance a substance in which there is only one type of particle; includes elements andcompounds (82)

Rradiation the transfer of energy through matter orspace as electromagnetic waves, such as visiblelight and infrared waves (255, 565)

radioactive decay the process in which thenucleus of a radioactive atom releases nuclearradiation (399)

radioactivity the ability of some elements to giveoff nuclear radiation (398)

radio waves EM waves with long wavelengths andlow frequencies (568)

RAM (random-access memory) computer memorythat stores information only while that informationis being used (497)

rarefaction (RER uh FAK shuhn) a region of lowerdensity or pressure in a wave (514, 534)

reactants (ree AK TUHNTS) the starting materials ina chemical reaction (354)

real image an image through which light passes(600)

reference point an object that appears to stay inplace in relation to an object being observed formotion (108)

reflection the bouncing back of a wave after itstrikes a barrier or an object (520, 545, 575)

refraction the bending of a wave as it passes atan angle from one medium to another (521, 577)

renewable resource a natural resource that can beused and replaced over a relatively short time (235)

resistance the opposition to the flow of electriccharge; expressed in ohms (Ω) (435)

resonance what occurs when an object vibratingat or near a resonant frequency of a second objectcauses the second object to vibrate (524, 550)

resonant frequencies the frequencies at whichstanding waves are made (524, 550)

resultant velocity the combination of two or morevelocities (111)

retina the back surface of the eye (605)

ROM (read-only memory) computer memory thatcannot be added to or changed (497)

Ssalt an ionic compound formed from the positiveion of a base and the negative ion of an acid (382)

saturated hydrocarbon a hydrocarbon in whicheach carbon atom in the molecule shares a singlebond with each of four other atoms; an alkane(388)

saturated solution a solution that contains all thesolute it can hold at a given temperature (94)

scattering the release of light energy by particlesof matter that have absorbed energy (577)

scientific method a series of steps that scientistsuse to answer questions and solve problems (11)

screw a simple machine that is an inclined planewrapped in a spiral (201)

secondary color cyan, magenta, and yellow; a colorof light produced when two primary colors of lightare added together (584)

semiconductor (SEM i kuhn DUHK tor) a sub-stance that conducts electric current better than aninsulator but not as well as a conductor (483)

series circuit a circuit in which all parts are con-nected in a single loop (442)


Glossary 759

GL

OS

SA

RY

signal something that represents information, suchas a command, a sound, or a series of numbersand letters (488)

simple machines the six machines from which all other machines are constructed: a lever, aninclined plane, a wedge, a screw, a wheel andaxle, and a pulley (198)

single-replacement reaction a reaction in which anelement takes the place of another element in acompound; this can occur only when a more-reactiveelement takes the place of a less-reactive one (359)

software a set of instructions or commands that tellsa computer what to do; a computer program (498)

solenoid a coil of wire that produces a magneticfield when carrying an electric current (463)

solid the state in which matter has a definiteshape and volume (61)

solubility (SAHL yoo BIL uh tee) the ability to dis-solve in another substance; more specifically, theamount of solute needed to make a saturatedsolution using a given amount of solvent at acertain temperature (44, 94)

solute the substance that is dissolved to form asolution (92)

solution a mixture that appears to be a singlesubstance but is composed of particles of two or more substances that are distributed evenlyamongst each other (92)

solvent the substance in which a solute is dis-solved to form a solution (92)

sonar (sound navigation and ranging) a type ofelectronic echolocation (546)

sonic boom the explosive sound heard when ashock wave from an object traveling faster thanthe speed of sound reaches a person’s ears (549)

sound energy the energy caused by an object’svibrations (220)

sound quality the result of several pitches blend-ing together through interference (552)

specific heat capacity the amount of energyneeded to change the temperature of 1 kg of asubstance by 1°C (256)

speed the rate at which an object moves; speeddepends on the distance traveled and the timetaken to travel that distance (109)

standing wave a wave that forms a stationary patternin which portions of the wave do not move and otherportions move with a large amplitude (524, 549)

states of matter the physical forms in which asubstance can exist; states include solid, liquid,gas, and plasma (60, 260)

static electricity the buildup of electric charges onan object (427)

sublimation (SUHB luh MAY shuhn) the change ofstate from a solid directly into a gas (72)

subscript a number written below and to the rightof a chemical symbol in a chemical formula (352)

surface tension the force acting on the particlesat the surface of a liquid that causes the liquid toform spherical drops (63)

surface wave a wave that occurs at or near theboundary of two media and that is a combinationof transverse and longitudinal waves (515)

suspension a mixture in which particles of amaterial are dispersed throughout a liquid or gasbut are large enough that they settle out (96)

synthesis (SIN thuh sis) reaction a reaction inwhich two or more substances combine to form asingle compound (358)

Ttechnology the application of knowledge, tools,and materials to solve problems and accomplishtasks; technology can also refer to the objectsused to accomplish tasks (11)

telecommunication the sending of informationacross long distances by electronic means (488)

temperature a measure of how hot (or cold) some-thing is; specifically, a measure of the averagekinetic energy of the particles in an object (26, 246)

terminal velocity the constant velocity of a fallingobject when the size of the upward force of airresistance matches the size of the downward forceof gravity (140)

theory a unifying explanation for a broad range ofhypotheses and observations that have been sup-ported by testing (19, 280, 328)

thermal energy the total energy of the particlesthat make up an object (218, 252)

thermal equilibrium the point at which twoobjects reach the same temperature (252)

thermal expansion the increase in volume of asubstance due to an increase in temperature (248)

thermal pollution the excessive heating of a bodyof water (269)

thermocouple a device that converts thermalenergy into electrical energy (432)

thrust the forward force produced by an airplane’sengines; thrust opposes drag (175)


Glossary760

GL

OS

SA

RY

tinnitus hearing loss resulting from damage to thehair cells and nerve endings in the cochlea (538)

tracer a radioactive element whose path can befollowed through a process or reaction (405)

transformer a device that increases or decreasesthe voltage of alternating current (472)

transistor an electronic component that can beused as an amplifier or a switch (485)

translucent the term describing matter that trans-mits light but also scatters the light as it passesthrough the matter (582)

transmission the passing of light through matter (581)

transparent the term describing matter throughwhich light is easily transmitted (582)

transverse wave a wave in which the particles ofthe wave’s medium vibrate perpendicular to thedirection the wave is traveling (513)

trough the lowest point of a transverse wave (513)

turbulence an irregular or unpredictable flow offluids that can cause drag; lift is often reduced byturbulence (176)

Uultrasonic the term describing sounds with fre-quencies higher than 20,000 Hz (541)

ultrasonography a medical procedure that usesechoes from ultrasonic waves to “see” inside apatient’s body without performing surgery (547)

ultraviolet light EM waves that are betweenvisible light and X rays in the electromagneticspectrum (573)

unbalanced forces forces on an object that cause thenet force to be other than zero; unbalanced forcesproduce a change in motion or acceleration (117)

unsaturated hydrocarbon a hydrocarbon in whichat least two carbon atoms share a double bond(an alkene) or a triple bond (an alkyne) (388)

Vvalence (VAY luhns) electrons the electrons in theoutermost energy level of an atom; these electronsare involved in forming chemical bonds (329)

vapor light light produced when electrons com-bine with gaseous metal atoms (597)

vaporization the change of state from a liquid toa gas; includes boiling and evaporation (70)

velocity (vuh LAHS uh tee) the speed of an objectin a particular direction (110)

vibration the complete back-and-forth motion ofan object (534)

virtual image an image through which light doesnot actually pass (599)

viscosity (vis KAHS uh tee) a liquid’s resistance toflow (63)

visible light the very narrow range of wavelengthsand frequencies in the electromagnetic spectrumthat humans can see (572)

voltage the difference in energy per unit charge asa charge moves between two points in an electriccircuit (same as potential difference); expressed involts (V) (434)

volume the amount of space that something occu-pies or the amount of space that something con-tains (25, 36)

Wwatt (W) the unit used to express power; equiva-lent to joules per second (J/s) (191)

wave a disturbance that transmits energy throughmatter or space (510, 535)

wavelength the distance between one point on awave and the corresponding point on an adjacentwave in a series of waves (517)

wave speed the speed at which a wave travels(519)

wedge a simple machine that is a double inclinedplane that moves; a wedge is often used forcutting (201)

weight a measure of the gravitational force exertedon an object, usually by the Earth (40, 128)

wheel and axle a simple machine consisting oftwo circular objects of different sizes; the wheel isthe larger of the two circular objects (202)

work the action that results when a force causes anobject to move in the direction of the force (188)

work input the work done on a machine; theproduct of the input force and the distancethrough which it is exerted (193)

work output the work done by a machine; theproduct of the output force and the distancethrough which it is exerted (193)

XX rays high-energy EM waves that are betweenultraviolet light and gamma rays in the electro-magnetic spectrum (574)



Glossary 761

SP

AN

ISH

GL

OS

SA

RY

Aabsolute zero/cero absoluto la temperatura másbaja posible (0º K, -273º C) (249)

absorption/absorción la transferencia de energíade las ondas luminosas a las partículas de materia(576)

acceleration/aceleración la proporción a quecambia la velocidad; un objeto se acelera sicambia su velocidad, si cambia su dirección, o sicambian su velocidad y su dirección (112)

acid/ácido cualquier compuesto que aumenta denúmero de iones de hidrógeno cuando se lodisuelve en agua, y cuya solución tiene saboramargo y puede cambiar el color de ciertoscompuestos; los ácidos hacen que el papel detornasol azul se vuelva rojo, reaccionan con losmetales para producir gas hidrógeno, y reaccionancon cal o con bicarbonato de sodio para producirgas dióxido de carbono (377)

activation energy/energía de activación lacantidad mínima de energía que requieren lassustancias para tener una reacción (362)

active solar heating/calefacción solar activasistema que consiste de colectores de energíasolar y una red de tubos que distribuyen laenergía solar por un edificio (265)

alkali metals/metales alcalinos los elementos enel Grupo 1 de la tabla periódica; son los metalesmás reactivos; sus átomos tienen un electrón ensu nivel exterior (310)

alkaline-earth metals/metales alcalinotérreoslos elementos en el Grupo 2 de la tabla periódica,son metales reactivos pero son menos reactivosque los metales alcaloides; sus átomos tienen doselectrones en su nivel exterior (311)

alloys/aleaciones soluciones sólidas de metales,o de no metales disueltos en metales (93)

alpha decay/desintegración alfa la liberación deuna partícula alfa de un núcleo (399)

alpha particle/partícula alfa tipo de radiaciónnuclear que consiste de dos protones y de dosneutrones emitidos por el núcleo de un átomoradioactivo; es idéntica al núcleo de un átomo dehelio (399)

alternating current/corriente alterna corrienteeléctrica en la cual las cargas continuamentecambian de fluir en una dirección a fluir en otra(434)

amplitude/amplitud la distancia máxima a la quevibra una onda a partir de su posición de des-canso (516, 543)

analog signal/señal analogica es una señal cuyaspropiedades, tales como amplitud y frecuencia,pueden cambiar continuamente según los cambiosen la información original; las señales de radioson señales análogas de ondas sonoras (489)

Archimedes’ principle/principio de Arquímedesel principio que establece que la fuerza deflotación sobre un objeto en un fluido es unafuerza hacia arriba igual al peso del volumen defluido desplazado por el objeto (168)

area/área la medida de la superficie que ocupaun objeto (26)

atmospheric pressure/presión atmosférica lapresión causada por el peso de la atmósfera (163)

atom/átomo la partícula más pequeña en la quepuede ser dividido un elemento y seguir siendo lamisma sustancia (280)

atomic mass/masa atómica el peso promedio delas masas de todos los isótopos de un elementoque ocurren de manera natural (292)

atomic mass unit (amu)/unidad de masa atómicala unidad del SI (estándard internacional) usadapara expresar las masas de las partículas en losátomos (288)

atomic number/número atómico el número deprotones en el núcleo de un átomo; el númeroatómico es el mismo para todos los átomos de unelemento (290)

average speed/velocidad promedio la velocidadgeneral a que se mueve un objeto; la velocidadpromedio puede calcularse dividiendo la distanciatotal por el tiempo total (109)

Bbalanced forces/fuerzas equilibradas las fuerzasque actúan sobre un objeto, que hacen que lafuerza neta sea cero; las fuerzas equilibradas nohacen que haya un cambio en el movimiento o laaceleración (118)

Spanish Glossary


Glossary762

SP

AN

ISH

GL

OS

SA

RY

base/base cualquier compuesto que aumenta elnúmero de iones hidroxilos cuando se disuelvenen agua, y cuya solución tiene sabor amargo, esviscosa, y puede cambiar el color de ciertoscompuestos; las bases hacen que el papel detornasol rojo se vuelva azul (379)

battery/batería un aparato formado por variascélulas que produce una corriente eléctrica al con-vertir energía química en energía eléctrica (430)

Bernoulli’s principle/principio de Bernoulli elprincipio que declara que cuando aumenta lavelocidad de un fluido en movimiento, disminuyela presión (173)

beta decay/desintegración beta cuando unapartícula beta se libera de un núcleo (400)

beta particle/partícula beta un electrón opositrón emitido por el núcleo de un átomoradioactivo (400)

bimetallic strip/tira bimetálica una tira formadaal poner dos metales diferentes uno sobre otro enuna tira larga y fina; como los metales diferentesse expanden a velocidades diferentes, una tirabimetálica puede enrollarse y desenrollarse conlos cambios en la temperatura; las tiras bimetáli-cas se usan en aparatos como los termostatos(250)

binary/binario dos; los números binarioscontienen sólo los dígitos 1 y 0 (490)

biochemicals/bioquímicos compuestos orgánicosformados por cosas vivas (384)

biomass/biomasa materia orgánica como plantas,madera, y desechos que contienen energía alma-cenada (236)

bit/bit el nombre para cada uno de los dígitos enun número binario (497)

block and tackle/aparejo de poleas una poleafija y una móvil que se usan juntas, puede teneruna gran ventaja mecánica si se usan varias poleas(204)

boiling/ebullición vaporización que ocurre en latotalidad de un líquido (70)

boiling point/punto de ebullición la temperaturaa que un líquido hierve y se transforma en gas(70)

Boyle’s law/ley de Boyle la ley que declara quepara una cantidad fija de gas a una temperaturaconstante, el volumen del gas aumenta aldisminuir la presión (65)

buoyant force/fuerza boyante la fuerza ascen-dente que los fluidos ejercen sobre toda materia;la fuerza de flotación se opone a la fuerza degravedad (168)

byte/byte unidad en que las computadoras alma-cenan y procesan información; es igual a ocho bits(497)

Ccalorie/caloría la cantidad de energía que senecesita para cambiar la temperatura de 0.001 kgde agua en 1ºC; una caloría es equivalente a4.184 J (258)

calorimeter/calorímetro aparato usado paradeterminar la capacidad específica de una sus-tancia para calor (258)

carbohydrates/carbohidratos sustancias bio-químicas compuestas por un azúcar simple o más,enlazados, que se usan como fuente de energía ypara almacenar energía (384)

catalyst/catalizador una sustancia que, sincambiar en forma permanente, aumenta lavelocidad a que ocurre una reacción (365)

cathode-ray tube CRT/tubo de rayo catódico untubo especial de vacío en el que un rayo deelectrones es proyectado en una pantalla; el rayode electrones produce las imágenes en unapantalla de televisión (493)

cell/célula aparato que produce una corrienteelécrica al convertir energía química en energíaeléctrica (430)

central processing unit CPU/unidad centralprocesadora el área física en la que la computa-dora lleva a cabo el trabajo (496)

centripetal acceleration/aceleración centrípetala aceleración que ocurre en un movimientocircular; un objeto que se mueve en un círculocambia de dirección constantemente, por lo que laaceleración ocurre continuamente (114)

change of state/cambio de estado la conversiónde una sustancia de una forma física a otra (68,261)

characteristic property/propiedad característicapropiedad de una sustancia que es siempre lamisma sin importar si la muestra en observaciónes pequeña o grande (48)

Charles’s law/ley de Charles ley que declara quepara una cantidad fija de gas a una presión con-stante, el volumen del gas aumenta al aumentarsu temperatura (66)


Glossary 763

SP

AN

ISH

GL

OS

SA

RY

chemical bond/lazo químico la fuerza deatracción que une a dos átomos (328)

chemical bonding/enlace químico la unión delos átomos para formar nuevas sustancias (328)

chemical change/cambio químico cambio queocurre cuando una o más sustancias se transfor-man en sustancias completamente nuevas, conpropiedades diferentes; no puede revertirseusando medios físicos (49, 262)

chemical energy/energía química la energía enun compuesto que cambia cuando sus átomos sevuelven a alinear para formar un nuevo com-puesto; la energía química es una forma deenergía potencial (218)

chemical equation/ecuación química descripciónresumida de una reacción química, expresada confórmulas y símbolos químicos (354)

chemical formula/fórmula química nota resu-mida para un compuesto o un elementodiatómico, expresada con símbolos químicos ynúmeros (352)

chemical property/propiedad química propiedadde la materia que describe a una sustancia enbase a su capacidad de convertirse en una nuevasustancia con propiedades diferentes (47)

chemical reaction/reacción química proceso porel cual una o más sustancias sufren un cambiopara producir una o más sustancias diferentes(350)

circuit/circuito una trayectoria completa y cerradaa través de la cual se mueven las cargas eléctricas(440)

circuit board/placa de circuito una colección decientos de circuitos muy pequeños que proveencorriente eléctrica a las varias partes de un aparatoelectrónico (482)

coefficient/coeficiente número que se poneantes de un símbolo químico o una fórmula; seusa para equilibrar la ecuación química (356)

colloid/coloide mezcla en la que las partículas sedispersan pero no tienen el peso suficiente paraasentarse (97)

combustion/combustión quemar combustible;específicamente, el proceso en el cual el com-bustible se combina con el oxígeno en un cambioquímico que produce energía térmica (266)

compound/compuesto una sustancia puracompuesta de dos o más elementos que estáncombinados químicamente (86)

compound machine/máquina compuestamáquina formada por dos máquinas simples omás (204)

compression/compresión región de mayordensidad o presión en una onda (514, 534)

computer/computadora aparato electrónico querealiza trabajos procesando y almacenando infor-mación (494)

concave lens/lente cóncava lente que es másfina en el medio que en los bordes (604)

concave mirror/espejo cóncavo espejo que securva hacia el centro, como la parte interior deuna cuchara (600)

concentration/concentración medida de lacantidad de un soluto disuelto en un solvente (94,364)

condensation/condensación cambio de estadode gas a líquido (71)

condensation point/punto de condensacióntemperatura a la cual un gas se vuelve líquido(71)

conduction (electrical)/conducción (eléctrica)método de cargar un objeto que ocurre cuandolos electrones se transfieren de un objeto a otropor contacto directo (425)

conduction (thermal)/conducción (térmica)transferencia de energía térmica de una sustanciaa otra por contacto directo; la conducción tambiénpuede ocurrir dentro de una sustancia (253)

conductor (electrical)/conductor (eléctrico) unmaterial en el cual se pueden mover fácilmentelas cargas (427)

conductor (thermal)/conductor (térmico) sustan-cia que conduce bien la energía termal (254)

constructive interference/interferencia construc-tiva interferencia que resulta en una onda conuna amplitud más grande quela de las ondasindividuales (523, 548, 579)

convection/convección la transferencia deenergía térmica por el movimiento de un líquido oun gas (254)

convection current/corriente de convección elmovimiento circular de líquidos o gases causadopor las diferencias en densidad que resultan de lasdiferencias en temperatura (254)

convex lens/lente convexa lente que es másgruesa en el medio que en los bordes (603)


Glossary764

SP

AN

ISH

GL

OS

SA

RY

convex mirror/espejo convexo espejo que securva hacia afuera, como la parte de afuera deuna cuchara (602)

cornea/córnea membrana transparente queprotege el ojo y refracta la luz (605)

covalent bond/enlace covalente la fuerza deatracción entre los núcleos de los átomos y loselectrones que los átomos comparten (336)

covalent compounds/compuestos covalentescompuestos formados por elementos que estánenlazados de forma covalente; estos compuestosestán formados por moléculas independientes,tienden a fundirse y a hacer ebullición a puntosbajos, en general no se disuelven en agua, y,cuando se disuelven, forman soluciones que noconducen corrientes eléctricas (375)

crest/cresta el punto más alto de una ondatransversal (513)

crystal lattice/estructura cristalina diseñotridimensional de iones, que se repite (335)

current/corriente un fluir continuo de cargacausado por el movimiento de electrones; lavelocidad a la que la carga pasa un punto dado;se expresa en amperes (A) (433)

Ddata/dato información recopilada medianteexperimentación (16)

decibel/decibelio la unidad más común usadapara expresar volumen de sonido (543)

decomposition reaction/reacción de descomposi-ción reacción en la cual un compuesto individualse descompone para formar dos o más sustanciasmás simples (359)

density/densidad la cantidad de materia en unespacio dado; masa por unidad de volumen (27,44, 165)

destructive interference/interferencia destructivainterferencia que resulta en una onda con unaamplitud menor que la de las ondas individuales(523, 548, 579)

diffraction/difracción cuando las ondas sedoblan alrededor de una barrera o a través de unaapertura (521, 551, 579)

digital signal/señal digital serie de pulsoseléctricos que representan los dígitos de númerosbinarios (490)

diode/diodo componente electrónico quepermite que la corriente eléctrica pase en una sola dirección (484)

direct current/corriente directa corriente eléctricaen que las cargas siempre fluyen en la mismadirección (434)

doping/adulteración el proceso de remplazaralgunos átomos de un semiconductor con algunosátomos de otra sustancia que tienen un númerodiferente de electrones de valencia; al implantarse cambia la disposición de los electrones en elsemiconductor (483)

Doppler effect/efecto de Doppler el cambioaparente en el tono de un sonido, causado por elmovimiento del que lo escucha o de la fuente delsonido (sólo se refiere a sonido) (542)

double-replacement reaction/reacción de sustitu-ción doble reacción en la que los iones en doscompuestos cambian de lugar; con frecuencia, unode sus productos es un gas o un precipitado (360)

drag/draga la fuerza que se opone al movimientoen un líquido o que lo restringe; el arrastre seopone al impulso (176)

ductility/ductilidad la capacidad de una sustanciade ser arrastrada o atraída al interior de un cable(44, 340)

Eecho/eco una onda sonora reflejada (520, 545)

echolocation/ecolocación proceso de usar ondassonoras reflejadas para encontrar objetos (546)

electrical energy/energía eléctrica la energía delos electrones en movimiento (219)

electric discharge/descarga eléctrica cuando lascargas se retiran de un objeto (428)

electric field/campo eléctrico la región alrededorde una partícula con carga que puede ejercer unafuerza sobre otra partícula con carga (423)

electric force/fuerza eléctrica la fuerza entre losobjetos con carga (423)

electric motor/motor eléctrico aparato que cam-bia la energía eléctrica a energía cinética (466)

electric power/fuerza eléctrica la velocidad a laque se usa la energía eléctrica para hacer trabajo;se expresa en vatios (437)


Glossary 765

SP

AN

ISH

GL

OS

SA

RY

electrode/electrodo la parte de una pila a travésde la cual entran o salen las cargas (430)

electrolyte/electrolito en una pila, la mezcla desustancias químicas que conducen la corrienteeléctrica (430)

electromagnet/electroimán un imán que consistede un solenoide que envuelve un centro de hierro(464)

electromagnetic induction/inducción electro-magnética el proceso por el cual se produce unacorriente eléctrica al cambiar un campo magnético(469)

electromagnetic spectrum/espectro electro-magnético la gama completa de ondas electro-magnéticas (567)

electromagnetic wave/onda electromagnéticaonda que puede viajar a través del espacio o de lamateria y que consiste de campos eléctricos ymagnéticos que cambian (492, 512, 564)

electromagnetism/electromagnetismo la interac-ción entre la electricidad y el magnetismo (463)

electron clouds/nubes de electrones regionesdentro de un átomo donde es probable encontrarelectrones (286)

electrons/electrones las partículas con carganegativa que se encuentran en todos los átomos;los electrones intervienen en la formación deenlaces químicos (283)

element/elemento sustancia pura que no puedesepararse o dividirse en sustancias más simplespor medios físicos o químicos (82)

endothermic/endotérmico término usado paradescribir un cambio físico o químico en el que seabsorbe la energía (69, 362)

energy/energía la capacidad de hacer trabajo(214)

energy conversion/conversión de energíacambio de una forma de energía a otra; cualquierforma de energía puede convertise en otra formade energía (222)

energy efficiency/eficiencia energética com-paración de la cantidad de energía antes de unaconversión y la cantidad de energía útil luego dela conversión (228)

energy resource/recurso energético recursonatural que los seres humanos pueden convertiren otras formas de energía para hacer trabajo útil(232)

evaporation/evaporación vaporización queocurre en la superficie de un líquido antes dellegar a su punto de ebullición (70)

exothermic/exotérmico término usado paradescribir un cambio físico o químico en el que selibera o se extrae energía (69, 361)

external combustion engine/motor de com-bustión externa un motor a calor que quemacombustible fuera del motor, como un motor avapor (266)

Ffiber optics: transmisión por fibra óptica el usode fibras ópticas (alambres de metal finos yflexibles) para transmitir luz a través de largasdistancias (612)

fixed pulley/polea fija una polea que está unidaa algo que no se mueve; las poleas fijas cambianla dirección de la fuerza pero no aumentan lafuerza (203)

fluid/fluido cualquier material que puede fluir yque toma la forma del recipiente que lo contiene(162)

fluorescent light/luz fluorescente luz visibleemitida por una partícula de fósforo cuandoabsorbe energía, como la luz ultravioleta (596)

focal length/distancia focal la distancia entre unespejo o una lente y su punto de foco (600)

focal point/punto focal el punto en el eje de unespejo o una lente a través del cual se enfocantodos los rayos incidentes de luz paralela (600)

force/fuerza lo que empuja o arrastra; todas lasfuerzas tienen tamaño y dirección (115)

fossil fuels/combustibles fósiles recursosenergéticos no renovables que se formaron através de millones de años en la corteza terrestrede los restos enterrados de organismos que enalgún momento estuvieron vivos (232)

free fall/caída libre la condición en que está unobjeto cuando la gravedad es la única fuerza queactúa sobre él (141)

freezing/congelación cambio de estado delíquido a sólido (69)

freezing point/punto de congelación la tem-peratura a la que un líquido se transforma ensólido (69)


Glossary766

SP

AN

ISH

GL

OS

SA

RY

frequency/frecuencia el número de ondas pro-ducido en un período de tiempo dado (518, 540)

friction/rozamiento fuerza que se opone almovimiento entre dos superficies que se tocan(119, 229)

fulcrum/punto de apoyo el punto fijo alrededordel cual rota una palanca (198)

fundamental/vibración fundamental la frecuen-cia de resonancia más baja (550)

Ggamma decay/desintegración gamma la libera-ción de rayos gamma de un núcleo (400)

gamma rays/rayos gamma ondas electromagnéti-cas con energía muy alta y sin masa ni carga;estos rayos son emitidos por el núcleo de unátomo radioactivo (400, 574)

gas/gaseoso estado en que la materia cambia enforma y en volumen (63)

generator/generador aparato que usa lainducción electromagnética para convertir laenergía cinética en energía eléctrica (470)

geothermal energy/energía geotérmica energíaque resulta del calentamiento de la corteza de laTierra (236)

gravitational potential energy/energía potencialde gravedad energía que se debe a la posiciónde un objeto sobre la superficie de la Tierra (216)

gravity/gravedad fuerza de atracción entreobjetos que se debe a sus masas (39, 125)

greenhouse effect/efecto invernadero el procesonatural de calentamiento de un planeta, como laTierra, en el que los gases en la atmósfera atrapanenergía térmica (255)

group/grupo columna de elementos en la tablaperiódica (309)

Hhalf-life/vida media el tiempo que le lleva a lamitad de los núcleos de un isótopo radioactivopara desintegrarse (404)

halogens/halógenos los elementos en el Grupo17 de la tabla periódica; son metaloides muyreactivos, y sus átomos tienen siete electrones ensu nivel externo (316)

hardware/hardware el conjunto de elementosfísicos que forman una computadora (496)

heat/calor la tranferencia de energía entre obje-tos que tienen temperaturas diferentes; la energíasiempre se transfiere de los objetos que tienentemperatura más alta a los que la tienen más bajahasta que se llega al equilibrio térmico; (251)también es la cantidad de energía que se trans-fiere entre objetos a diferentes temperaturas (257)

heat engine/motor térmico una máquina queusa calor para funcionar (266)

hertz/hertzio la unidad usada para expresarfrecuencia; un herzio es un ciclo por segundo(518, 540)

heterogeneous mixture/mezcla heterogéneacombinación de sustancias en la que los dife-rentes componentes se pueden observar confacilidad (96)

hologram/holograma trozo de película en el queun diseño de interferencia produce la imagentridimensional de un objeto (611)

homogeneous mixture/mezcla homogénea com-binación de sustancias en que la apariencia y laspropiedades son iguales en toda la mezcla (92)

hydraulic device/aparato hidráulico aparato queusa líquidos para transmitir presión de un punto aotro (167)

hydrocarbons/hidrocarburos componentesorgánicos que están compuestos solamente decarbón e hidrógeno (388)

hypothesis/hipótesis posible explicación orespuesta para una pregunta (14)

Iideal machine/máquina ideal una máquina 100por ciento eficiente (197)

illuminated/iluminado término que describeobjetos visibles que no son fuentes de luz (594)

incandescent light/luz incandescente luzproducida por objetos calientes (595)

inclined plane/plano inclinado una máquinasimple formada por una superficie plana, incli-nada; una rampa (200)

induction/inducción método de cargar un objeto;ocurre cuando, en un objeto sin carga, las cargasse vuelven a ordenar sin contacto directo con unobjeto con carga (425)


Glossary 767

SP

AN

ISH

GL

OS

SA

RY

inertia/inercia la tendencia de todos los objetosde resistir los cambios en su movimiento (42,147)

infrared waves/ondas infrarrojas ondas electro-magnéticas que existen en el espectro electromag-nético entre las microondas y la luz visible (571)

infrasonic/infrasónico término que describe lossonidos con frecuencias más bajas que 20 hertzios(541)

inhibitor/inhibidor sustancia que detiene o hacemás lenta una reacción química (365)

inner ear/oído interno la parte del oído en quelas vibraciones creadas por el sonido se cambianen señales eléctricas que el cerebro puedeinterpretar (537)

input/datos entrados la información que se da auna computadora (494)

input device/unidad de entrada la parte de lacomputadora que le proporciona la información(496)

input force/fuerza de entrada la fuerza que seaplica a una máquina (193)

insulation/aislamiento sustancia que reduce latransferencia de energía térmica (264)

insulator (electrical)/aislante (eléctrico) materialen el que las cargas no se pueden mover confacilidad (427)

insulator (thermal)/aislante (térmico) materialque no es buen conductor de energía térmica(254)

integrated circuit/circuito integrado circuitocompleto que contiene muchos transistores yotros componentes electrónicos en un chip desilicona único (486)

interference/interferencia interacción de ondasque ocurre cuando dos o más ondas sesuperponen (522, 548, 579)

internal combustion engine/motor de com-bustión interna un motor de calor que quemacombustible dentro del motor, como por ejemplo,un motor de automóvil (267)

Internet/Internet una red gigante de computa-doras, que consiste de millones de computadorasque pueden compartir información una con otra(499)

ionic bond/enlace iónico la fuerza de atracciónentre iones con cargas opuestas (332)

ionic compounds/compuestos iónicos com-puestos que contienen enlaces iónicos; estánformados por iones dispuestos en una estructruracristalina, tienden a tener puntos de fusión y deebullición altos, son sólidos a temperatura am-biente, y se disuelven en agua para formar solu-ciones conductoras de corriente eléctrica (374)

ions/iones partículas con carga que se formandurante cambios químicos cuando uno o máselectrones de valencia pasan de un átomo a otro(332)

iris/iris la parte coloreada del ojo (605)

isotopes/isótopos átomos que tienen el mismonúmero de protones pero un número diferente deneutrones (290, 400)

Jjoule/joule la unidad usada para expresar trabajoy energía; es equivalente al newton-metro (N.m)(190)

Kkilocalorie/kilocaloría la unidad de energía iguala 1,000 calorías; la kilocaloría también se conocecomo la Caloría, que es la unidad de energía queaparece en las etiquetas de los alimentos (258)

kinetic energy/energía cinética la energía delmovimiento; depende de la velocidad y la masa(215)

Llaser/láser un aparato que produce luz intensade sólo un color y una longitud de onda (609)

law/ley un resumen de muchos resultados yobservaciones de experimentos; la ley dice cómofuncionan las cosas (19)

law of conservation of energy/ley de conser-vación de energía la ley que establece que laenergía no se crea ni se destruye (230, 362)

law of conservation of mass/ley de conservaciónde materia la ley que establece que la masa ni secrea ni se destruye con los cambios químicos yfísicos comunes (357)

law of electrical charges/ley de cargas eléctricasla ley que establece que las cargas iguales serepelen y las opuestas se atraen (423)


Glossary768

SP

AN

ISH

GL

OS

SA

RY

law of reflection/ley de reflexión la ley queestablece que el ángulo de incidencia es igual alángulo de reflexión (575)

law of universal gravitation/ley de gravitaciónuniversal la ley que establece que todos losobjetos en el universo se atraen mutuamente porla fuerza de gravedad; el tamaño de la fuerzadepende de la masa de los objetos y de ladistancia entre ellos (126)

lens/lente un objeto curvo, transparente, queforma una imagen al refractar la luz (603);también es la parte del ojo que refracta la luz para enfocar una imagen en la retina (605)

lever/palanca una máquina simple que consisteen una barra que rota alrededor de un punto fijo,llamado punto de apoyo; hay tres clases depalancas, dependiendo de dónde se encuentran lafuerza de entrada, la fuerza de salida y el puntode apoyo con respecto a la carga: palancas deprimera clase, de segunda clase, y de tercera clase(198)

lift/elevación fuerza ascendente sobre un objeto(como un ala), causada por diferencias en lapresión arriba y abajo del objeto; la elevación seopone al arrastre de la gravedad (174)

light energy/energía de la luz la energíaproducida por las vibraciones de las partículascargadas con electricidad (220)

lipids/lípidos sustancias bioquímicas que no sedisuelven en agua; sus funciones incluyenalmacenar energía y formar membranas celulares;los lípidos incluyen las ceras, las grasas, y losaceites (385)

liquid/líquido el estado en que la materia tomala forma de su recipiente y tiene un volumendefinido (62)

load/cargador aparato que usa energía eléctricapara funcionar (440)

longitudinal wave/onda longitudinal una ondaen que las partículas del medio vibran haciaadelante y hacia atrás en la trayectoria de la onda(514)

loudness/sonoridad la percepción de si unsonido es fuerte o suave (542)

lubricant/lubricante una sustancia que se aplicaa las superficies para reducir la fricción entre ellas(123)

luminous/luminoso término que describe losobjetos que producen luz visible (594)

Mmachine/máquina un aparato que ayuda a hacerque el trabajo sea más fácil al cambiar el tamañoy/o la dirección de una fuerza (192)

magnet/imán cualquier material que atrae alhierro o a los materiales que contienen hierro(454)

magnetic field/campo magnético regiónalrededor de un imán sobre la que actúan lasfuerzas magnéticas (456)

magnetic force/fuerza magnética la fuerza derepulsión o de atracción entre los polos de losimanes (455)

malleability/maleabilidad la capacidad de unasustancia de ser martillada y convertida en hojasfinas (44, 340)

mass/masa la cantidad de materia de que estáhecho algo; su valor no cambia con la situacióndel objeto en el universo (26, 38, 129)

mass number/número de masa la suma de losprotones y neutrones en un átomo (291, 399)

matter/materia cualquier cosa que tengavolumen y masa (7, 36)

mechanical advantage/ventaja mecánica unnúmero que indica las veces que una máquinamultiplica la fuerza; se puede calcular dividiendola fuerza de salida por la fuerza de entrada (196)

mechanical efficiency/eficiencia mecánicacomparación del rendimiento de salida de unamáquina y su rendimiento de entrada, expresadacomo porcentaje, se puede calcular dividiendo elrendimiento de salida por el rendimiento deentrada y luego multiplicando por 100 (197)

mechanical energy/energía mecánica la energíatotal del movimiento y posición de un objeto(217)

medium/medio sustancia a través de la cualpuede viajar una onda (511, 536)

melting/fusión cambio de estado de sólido alíquido (69)

melting point/punto de fusión la temperatura ala cual una sustancia cambia de sólido a líquido(69)

memory/memoria el lugar donde una computa-dora almacena información (494)


Glossary 769

SP

AN

ISH

GL

OS

SA

RY

meniscus/menisco la curvatura en la superficiede un líquido por la que se mide el volumen dellíquido (37)

metallic bond/enlace metálico la fuerza deatracción entre un ion metálico con carga positivay los electrones en un metal (339)

metalloids/metaloides elementos que tienenpropiedades tanto de los metales como de los nometales; algunas veces se los llama semicon-ductores (85)

metals/metales elementos que brillan y que sonbuenos conductores de energía térmica y corrienteeléctrica; la mayoría de los metales son maleablesy dúctiles (85)

meter/metro la unidad básica de longitud en elsistema SI (25)

microprocessor/microprocesador un circuitointegrado que contiene muchas de las capaci-dades de una computadora en un solo chip desilicona (495)

microwaves/microondas ondas electromag-néticas que se encuentran entre las ondas deradio y las ondas infrarrojas en el espectroelectromagnético (570)

middle ear/oído medio la parte del oído dondese aumenta la amplitud de las vibraciones desonido (537)

mixture/mezcla la combinación de dos o mássustancias que no están combinadas química-mente (90)

model/modelo representación de un objeto osistema (20, 283)

modem/modem parte física de una computadoraque permite que las computadoras se comu-niquen por líneas telefónicas (497)

molecule/molécula grupo neutral de átomos quese mantienen unidos por enlaces covalentes (336)

momentum/momento propiedad de un objeto enmovimiento que depende de la masa y velocidaddel objeto (152)

motion/movimiento el cambio de posición de unobjeto a través del tiempo cuando se lo comparacon un punto de referencia (108)

movable pulley/polea móvil una polea fijada alobjeto que se mueve; las poleas móviles aumen-tan la fuerza (203)

Nnegative acceleration/aceleración negativaaceleración en la que la velocidad disminuye,también se llama deceleración (113)

neon light/luz de neón luz emitida por losátomos de ciertos gases como el neón, cuandoabsorben y luego liberan energía (596)

net force/fuerza resultante la fuerza que resultaal combinar todas las fuerzas ejercidas sobre unobjeto (116)

neutrons/neutrones las partículas del núcleo queno tienen carga (288)

newton/newton la unidad de fuerza del SI (41,115)

noble gases/gases nobles los elementos norectivos en el Grupo 18 de la tabla periódica; susátomos tienen ocho electrones en su nivel exterior(excepto el helio, que tiene dos electrones) (316)

noise/ruido cualquier sonido no deseado,especialmente un sonido no musical, que incluyeuna mezcla accidental de tonos (555)

nonmetals/no metales elementos que soninactivos y malos conductores de energía térmica ycorriente eléctrica (85)

nonrenewable resource/recursos no renovablesrecursos naturales que no se pueden remplazar oque pueden remplazarse sólo luego del paso demiles o millones de años (232)

nuclear chain reaction/reacción nuclear encadena una serie continua de reacciones defisión nuclear (407)

nuclear energy/energía nuclear la forma deenergía asociada con los cambios en el núcleo deun átomo, un recurso de energía alternativa (221)

nuclear fission/fisión nuclear el proceso en queun núcleo grande se divide en dos núcleos máspequeños (235, 406)

nuclear fusion/fusión nuclear el proceso en quedos o más núcleos con poca masa se unen, o sefunden, para formar un núcleo más grande y másmasivo (410)

nuclear radiation/radiación nuclear partículas yrayos de alta energía emitidos por el núcleo dealgunos átomos; las partículas alfa, las partículasbeta, y los rayos gamma son tipos de radiaciónnuclear (398)


Glossary770

SP

AN

ISH

GL

OS

SA

RY

nucleic acids/ácidos nucleicos sustanciasbioquímicas que almacenan información y ayudana formar proteínas y otros ácidos nucleicos;formadas por subunidades llamadas nucleótidos(387)

nucleus: núcleo la pequeña región extremada-mente densa y con carga positiva en el centro deun átomo; formada por protones y neutrones(285)

Oobservation/observación cualquier uso de lossentidos para reunir información (12)

Ohm’s law/ley de Ohm la ley que establece larelación entre corriente (I), voltaje (V) y resistencia(R); expresada con la ecuación I=V/R (437)

opaque/opaco término que describe la materiaque no trasmite ninguna luz (582)

optical axis/eje óptico línea recta trazada haciaafuera desde el centro de un espejo o lente (600)

organic compounds/compuestos orgánicoscompuestos covalentes formados por moléculascon base de carbono (383)

oscilloscope/osciloscopio aparato usado pararepresentar gráficamente las ondas sonoras (544)

outer ear/oído externo la parte del oído queactúa como embudo para dirigir las ondas sonorashacia el oído medio (537)

output/salida el resultado final del procesa-miento o la prueba del trabajo realizado por unacomputadora (494)

output device/unidad de salida parte de lacomputadora en que se muestran los resultadosde hacer un trabajo (497)

output force/fuerza de salida la fuerza aplicadapor una máquina (193)

overtones/armónicos frecuencias resonantes queson más altas que las fundamentales (550)

Pparallel circuit/circuito en paralelo circuito en el cual las diferentes cargas están en ramasseparadas (443)

pascal/pascal la unidad SI de presión (Pa); esigual a la fuerza de un newton ejercida sobre unárea de un metro cuadrado (162)

Pascal’s principle/principio de Pascal principioque establece que un cambio en presión encualquier punto de un fluido se trasmite a todaslas partes de ese fluido por igual (167)

passive solar heating/calefacción solar pasivasistema de calefacción solar que depende deparedes gruesas y ventanas grandes para usar laenergía del sol como medio de calefacción (265)

period/período una hilera horizontal de elemen-tos en la tabla periódica (309)

periodic/periódico que tiene una configuraciónregular que se repite (302)

periodic law/ley periódica la ley que estableceque las propiedades químicas y físicas de los ele-mentos son funciones periódicas de sus númerosatómicos (303)

perpendicular/perpendicular a ángulos rectos(513, 564)

perpetual motion machine/máquina demovimiento perpetuo máquina que funcionapermanentemente sin que se le entre energía adi-cional; su rendimiento de energía sería igual a suentrada de energía; las máquinas de movimientoperpetuo son imposibles de crear (231)

pH/pH una medida de la concentración de ion dehidronio en una solución; un pH de 7 es neutro;un pH menor que 7 es ácido; y un pH mayor que7 es básico (380)

photocell/fotocélula la parte de un panel solarque convierte la luz en energía eléctrica (432)

photon/fotón un “paquete” de energía muypequeño liberado por un electrón que se mueve aun nivel de energía más bajo en un átomo (565)

physical change/cambio físico un cambio queafecta una o más de las propiedades físicas deuna sustancia, los cambios físicos con frecuenciason fáciles de hacer (48, 261)

physical property/propiedad física unapropiedad de la materia que se puede observar omedir sin cambiar la identidad de la materia (43)

physical science/ciencia física el estudio de lamateria y la energía (7)

pigment/pigmento un material que le da su colora una sustancia al absorber algunos colores de laluz y reflejar otros (584)

pitch/tono cómo se percibe un sonido, si esgrave o agudo (540)


Glossary 771

SP

AN

ISH

GL

OS

SA

RY

plane mirror/espejo plano un espejo con unasuperficie plana (599)

plasma/plasma el estado de la materia que notiene una forma o un volumen definido y cuyaspartículas se han separado; el plasma estácompuesto de electrones y iones con cargapositiva (67)

polarized light/luz polarizada consiste de ondasde luz que vibran en sólo un plano (unadirección) (612)

poles/polos las partes de un imán en que losefectos magnéticos son más fuertes (454)

positive acceleration/aceleración positiva laaceleración en que la velocidad aumenta (113)

positron/positrón partícula beta con una cargade 1+ y una masa de casi 0 (400)

potential difference/diferencia potencial energíapor unidad de carga; específicamente, la diferenciaen energía por unidad de carga al moverse lacarga entre dos puntos en un circuito eléctrico (lomismo que el voltaje); se expresa en voltios (431)

potential energy/energía potencial la energía deposición o forma (216)

power/poder la proporción a la que se hace eltrabajo (191)

pressure /presión la cantidad de fuerza que seejerce en un área determinada; la unidad SI parala presión es el pascal (64, 162)

primary colors of light/colores primarios de laluz rojo, azul, y verde; estos colores de la luz sepueden combinar en proporciones diferentes paraproducir todos los colores del espectro (584)

primary pigments/pigmentos primarios amarillo,cian, y magenta; estos pigmentos se pueden com-binar para producir cualquier otro pigmento (585)

products/productos las sustancias formadas poruna reacción química (354)

projectile motion/movimiento proyectil elmovimiento curvo que sigue un objeto cuando eslanzado cerca de la superficie de la Tierra (143)

proteins/proteínas sustancias bioquímicas queestán compuestas de aminoácidos; sus funcionesincluyen regular las actividades químicas, trans-portar y almacenar materiales, y dar apoyoestructural (386)

protons/protones las partículas con carga positivadel núcleo; el número de protones en un núcleoes el número atómico que determina la identidadde un elemento (288)

pulley/polea una máquina simple que consistede una rueda con ranuras que sostiene unacuerda o un cable; hay dos clases de poleas, lasfijas y las móviles (203)

pupil/pupila la apertura hacia el interior del ojo(605)

pure substance/sustancia pura una sustancia enla que hay solamente una clase de partícula;incluye elementos y compuestos (82)

Rradiation/radiación la transferencia de energíatérmica a través del espacio en forma de ondaselectromagnéticas, como la luz visible y las ondasinfrarrojas (255, 565)

radioactive decay/desintegración radioactiva elproceso en el cual el núcleo de un átomoradioactivo libera radiación nuclear (399)

radioactivity/radioactividad la capacidad dealgunos elementos de despedir radiación nuclear(398)

radio waves/ondas de radio ondas electromag-néticas con longitud de onda larga y frecuenciascortas (568)

RAM (random-access memory)/RAM (memoriade acceso aleatorio) memoria de la computadoraque almacena la información solamente cuandoesa información está en uso (497)

rarefaction/rarefacción una región de densidad opresión más baja en una onda (514, 534)

reactants/reactivos los materiales que dancomienzo a una reacción química (354)

real image/imagen real imagen a través de lacual pasa la luz (600)

reference point/punto de referencia un objetoque parece estar inmóvil en relación a otro objetoque se observa en movimiento (108)

reflection/reflexión momento en que una ondarebota luego de chocar contra una barrera o unobjeto (520, 545, 575)

refraction/refracción cuando una onda se doblaal pasar de un medio a otro (521, 577)

Glossary772

SP

AN

ISH

GL

OS

SA

RY

renewable resource/recurso renovable unrecurso natural que puede usarse y serremplazado en un período de tiempo corto (235)

resistance/resistencia la oposición al flujo decargas eléctricas; se expresa en ohms (435)

resonance/resonancia lo que ocurre cuando unobjeto que vibra en la frecuencia resonante de unsegundo objeto o cerca de él, hace que elsegundo objeto vibre también (524, 550)

resonant frequencies/frecuencias de resonancialas frecuencias a que se hacen las ondasestacionarias (524, 550)

resultant velocity/velocidad resultante lacombinación de dos o más velocidades (111)

retina/retina la superficie de atrás del ojo (605)

ROM (read-only memory)/ROM (memoria sinacceso directo) la memoria que no se puedeaumentar ni cambiar en una computadora (497)

Ssalt/sal un compuesto iónico formado del ionpositivo de una base y del ion negativo de unácido (382)

saturated hydrocarbon/hidrocarburo saturadoun hidrocarburo en que cada átomo de carbonoen la molécula comparte un enlace simple conuno de otros cuatro átomos; un alcano (388)

saturated solution/solución saturada soluciónque contiene todo el soluto que puede contener auna temperatura dada (94)

scattering/dispersión cuando las partículas demateria que han absorbido energía despiden luzcomo energía (577)

scientific method/método científico serie depasos que los científicos usan para responderpreguntas y resolver problemas (11)

screw/tornillo una máquina simple que es unplano inclinado envuelto en un espiral (201)

secondary color/color secundario cian, magenta,y amarillo; un color producido al combinar doscolores primarios (584)

semiconductor/semiconductor sustancia queconduce la corriente eléctrica mejor que unaislante pero no tan bien como un conductor(483)

series circuit/circuito en serie circuito en quetodas las partes están conectadas en un lazo sim-ple (442)

signal/señal algo que representa información,como una orden, un sonido, o una serie denúmeros y letras (488)

simple machines/máquinas simples las seismáquinas con las que se construyen todas lasotras: una palanca, un plano inclinado, una cuña,un tornillo, una rueda y eje, y una polea (198)

single-replacement reaction/reacción de sustitu-ción simple reacción en la que un elementotoma el lugar de otro en un compuesto; puedeocurrir solamente cuando un elemento más reac-tivo toma el lugar de otro menos reactivo (359)

software/software serie de instrucciones uórdenes que le dicen a una computadora quédebe hacer (498)

solenoid/solenoide un espiral de alambre queproduce un campo magnético cuando lleva unacorriente eléctrica (463)

solid/sólido el estado en que la materia tieneforma y volumen definidos (61)

solubility/solubilidad la capacidad de disolverseen otra sustancia; más específicamente, lacantidad de soluto que se necesita para hacer unasolución saturada usando una cierta cantidad desolvente a una cierta temperatura (44, 94)

solute/substancia por disolver la sustancia quese disuelve para formar una solución (92)

solution/solución mezcla que parece unasustancia simple, pero está compuesta de laspartículas de dos o más sustancias que sedistribuyen igualmente entre sí (92)

solvent/solvente la sustancia en la cual sedisuelve un soluto para formar una solución (92)

sonar (sound navigation and ranging)/sonar untipo de detección electrónica por ultrasonido(546)

sonic boom/estruendo sónico el sonido explo-sivo que se oye cuando la onda de choque pro-ducida por un objeto que viaja a más velocidadque la velocidad del sonido alcanza los oídos deuna persona (549)

sound energy/energía de sonido la energíacausada por las vibraciones de un objeto (220)


Glossary 773

SP

AN

ISH

GL

OS

SA

RY

sound quality/cualidad del sonido el resultadode varios tonos que se mezclan a través de inter-ferencia (552)

specific heat capacity/capacidad de calorespecífico la cantidad de energía que se necesitapara cambiar la temperatura de 1 kg de una sus-tancia en 1ºC; la capacidad para calor específicoes una propiedad característica de una sustancia(256)

speed/velocidad la velocidad a que se mueve unobjeto; la velocidad depende de la distancia a quese viaja y del tiempo que lleva recorrer esadistancia (109)

standing wave/onda estacionaria onda queforma un diseño estacionario en el que ciertaspartes de la onda no se mueven y otras partes semueven con una amplitud grande (524, 549)

states of matter/estados de la materia lasformas físicas en que puede existir una sustancia;los estados incluyen sólido, líquido, gas, y plasma(60, 260)

static electricity/electricidad estática laacumulación de cargas eléctricas en un objeto(427)

sublimation/sublimación el cambio de estado desólido directamente a un gas (72)

subscript/subíndice el número que se escribedebajo y a la derecha de un símbolo químico enuna fórmula química (352)

surface tension/tensión de la superficie lafuerza que actúa sobre las partículas en la super-ficie de un líquido, que causa que el líquido formegotas esféricas (63)

surface wave/onda superficial onda que ocurrecerca de o en el límite de dos medios y que esuna combinación de ondas transversales ylongitudinales (515)

suspension/suspensión mezcla en la cual laspartículas de un material se dispersan a través deun líquido o gas, pero como son lo suficiente-mente grandes, se asientan (96)

synthesis reaction/reacción de síntesis reacciónen la cual dos o más sustancias se combinan paraformar un compuesto único (358)

Ttechnology/tecnología la aplicación deconocimiento, instrumentos, y materiales pararesolver problemas y realizar tareas; la tecnologíatambién se puede referir a los objetos usados pararealizar tareas (11)

telecommunication/telecomunicación enviarinformación a través de grandes distancias pormedios electrónicos (488)

temperature/temperatura medida de cuáncaliente o frío es algo; específicamente, la medidade la energía cinética promedio de las partículasen un objeto (26, 246)

terminal velocity/velocidad terminal la velocidadconstante de un objeto que cae cuando la magni-tud de la fuerza ascendente de la resistencia delaire es igual a la magnitud de la fuerza degravedad hacia abajo (140)

theory/teoría la explicación que unifica una granvariedad de hipótesis y observaciones que hansido apoyadas por la experimentación (19, 280,328)

thermal energy/energía térmica totalidad de laenergía cinética de las partículas que forman unobjeto (218, 252)

thermal equilibrium/equilibrio térmico punto enel cual dos objetos llegan a la misma temperatura;cuando se está en equilibrio térmico no ocurreninguna transferencia neta de energía térmica(252)

thermal expansion/expansión termal el aumentoen volumen de una sustancia debido a unaumento en temperatura (248)

thermal pollution/polución térmica el calenta-miento excesivo de una extensión de agua (269)

thermocouple/par térmico aparato que conviertela energía térmica en energía eléctrica (432)

thrust/empuje la fuerza hacia adelante producidapor los motores de un avión; el impulso se oponeal arrastre (175)

tinnitus/tinnitus pérdida de audición que resultapor el daño a las células capilares y a las termina-ciones nerviosas en la cóclea (538)

tracer/indicador radioactivo un elementoradioactivo cuya trayectoria se puede seguir através de un proceso o reacción (405)

transformer/transformador aparato que aumentao disminuye el voltaje de corriente alterna (472)


Glossary774

SP

AN

ISH

GL

OS

SA

RY

transistor/transistor componente electrónico quese puede usar como amplificador o interruptor(485)

translucent/translúcido término que describe lamateria que transmite luz pero que la desparramacuando la luz la atraviesa (582)

transmission/transmisión cuando la luz pasa porla materia (581)

transparent/transparente término que describela materia a través de la cual la luz se transmitecon facilidad (582)

transverse wave/onda transversa onda cuyaspartículas del medio vibran perpendicularmente ala dirección en que se desplaza la onda (513)

trough/seno la parte más baja de una ondatransversal (513)

turbulence/turbulencia un fluir de líquidosirregular o impredecible que puede causararrastre; la elevación con frecuencia es reducidapor la turbulencia (176)

Uultrasonic/ultrasónico el término que describelos sonidos con frecuencias más altas que 20,000Hz (541)

ultrasonography/ultrasonograma procedimientomédico que usa ecos de ondas ultrasónicas para“ver” el interior del cuerpo del paciente sin hacercirugía (547)

ultraviolet light/luz ultravioleta ondas electro-magnéticas que están ubicadas entre la luz visibley los rayos X en el espectro electromagnético(573)

unbalanced forces/fuerzas en desequilibriofuerzas que actúan sobre un objeto, que causanque la fuerza neta sea diferente de cero; lasfuerzas en desequilibrio producen un cambio en elmovimiento o la aceleración (117)

unsaturated hydrocarbon/hidrocarburo nosaturado un hidrocarburo en el cual por lomenos dos átomos de carbono comparten unenlace doble (un alqueno) o un enlace triple (unalquino) (388)

Vvalence electrons/electrones de valenciaelectrones en el nivel de energía exterior en unátomo; estos electrones toman parte en laformación de enlaces químicos (329)

vapor light/luz de vapor luz que se producecuando los electrones se combinan con átomosgaseosos de metal (597)

vaporization/vaporización el cambio de estadode líquido a gas, incluye la ebullición y la evapo-ración (70)

velocity/velocidad vectorial la velocidad de unobjeto en una dirección específica (110)

vibration/vibración el movimiento completo deun objeto hacia adelante y hacia atrás (534)

virtual image/imagen virtual imagen a través dela cual en realidad no pasa la luz (599)

viscosity/viscosidad la resistencia de un líquido afluir (63)

visible light/luz visible la extensión muypequeña de longitud y frecuencias de onda en elespectro electromagnético que los humanospueden ver (572)

voltage/voltaje la diferencia en energía porunidad de carga cuando la carga se mueve entredos puntos en un circuito eléctrico (lo mismo quela diferencia potencial); se expresa en voltios(434)

volume/volumen la cantidad de espacio ocupadao contenida por algo (25, 36)

Wwatt/vatio la unidad que se usa para expresarelectricidad (W); es equivalente a joules porsegundo (J/s) (191)

wave/onda una alteración que transmite energíaa través de la materia o del espacio (510, 535)

wavelength/longitud de onda la distancia entreun punto en una onda y el punto correspondienteen una onda adyacente en una serie de ondas(517)

wave speed/velocidad de onda la velocidad aque viaja una onda (519)


Glossary 775

SP

AN

ISH

GL

OS

SA

RY

wedge/cuña una máquina simple formada por un plano inclinado doble que se mueve; confrecuencia se usa para cortar (201)

weight/peso medida de la fuerza de gravedadejercida sobre un objeto, usualmente por la Tierra(40, 128)

wheel and axle/rueda y eje una máquina simpleque consiste de dos objetos circulares dediferentes tamaños; la rueda es la más grande delos dos (202)

work/trabajo la acción que resulta cuando unafuerza hace que un objeto se mueva en ladirección de la fuerza (188)

work input/trabajo aplicado el trabajo que sehace en una máquina; el producto de la fuerza deentrada y la distancia a través de la que se ejerce(193)

work output/trabajo resultante el trabajo hechopor una máquina; el producto de la fuerza desalida y la distancia a través de la que se ejerce(193)

Xx rays/rayos X ondas electromagnéticas de altaenergía que están entre las onda ultravioletas y lasgamma en el espectro electromagnético (574)



Index776

IND

EX A boldface number refers to an

illustration on that page.

Aabsolute zero, 249, 274absorption, 576, 576–577acceleration, 112–114, 113

calculation of, 112–113centripetal, 114, 114defined, 112force and, 148–149gravitational, 138–139, 139,

144, 144, 149negative, 113Newton’s second law and,

148–149positive, 113, 114units, 112

acid precipitation, 51, 381acids

defined, 377, 743hydrogen ions and, 377neutralization, 380–381, 381organic, 389pH scale and, 380, 380–381properties of, 377–378strong versus weak, 378tannic, 394uses of, 378

action force, 150, 150–151, 151activation energy, 348, 362,

363, 365active solar heating, 265air, 92, 96, 170, 174–177, 264air bags, 348, 348aircraft, 136, 174, 174airplanes, 62, 136, 174–176,

174–176air pressure, 162. See also

atmospheric pressureair resistance, 139–141, 141

terminal velocity and, 140alcohols, 48, 59, 389Alexander the Great, 281alkali metals, 310, 310–311alkaline-earth metals, 311alloys, 93

alpha particles, 399, 399, 401,402

alternating current (AC), 434, 434

aluminum, 88–89, 256, 287, 287, 314, 333, 333

amber, 283amino acids, 346, 386, 395ammonia, 89, 379amorphous solids, 61, 61Ampère, André-Marie, 463amperes, 433, 437amplitude, 516, 516–517

of sound waves, 542–544, 544

amplitude modulation (AM), 568–569, 569

analog signals, 488–490, 489, 490, 492

angle of incidence, 575, 575,747

angle of reflection, 575, 575, 576, 747

Archimedes’ principle, 104, 168–169, 747

area calculation of, 26, 26, 741force, pressure, and, 162

argon, 291, 316, 317Aristotle, 281armature, 466, 466ascorbic acid, 378astronomy, 9atmospheric pressure, 71,

162–164, 164, 166atomic mass, 292, 302–303atomic mass unit (amu), 288atomic nucleus, 276, 285, 288,

288atomic number, 290, 303, 742atomic theory, 23, 280–286, 286atoms, 276–293, 742

in chemical bonds, 328defined, 280, 742electrical energy and, 219electric charge and, 422–423forces in, 293size of, 287, 288structure of, 288, 288–289

Atzmon, Michael, 417, 417

auroras, 67, 461, 461automobiles. See carsaverage acceleration, 748averages, 738average speed, 109

calculation of, 109, 748azurite, 585

Bbaking soda, 48, 348, 348balanced forces, 118ball bearings, 123bar graphs, 737, 737barium, 406baseball, 177bases

defined, 379, 743hydroxide ions and, 379neutralization, 380–381, 381pH scale and, 380, 380–381properties of, 379, 379strong versus weak, 380uses of, 379, 379

batteries, 225, 430, 430, 431, 431, 434–435

Becquerel, Henri, 325, 398Bell, Alexander Graham, 419beluga whales, 545, 545benzene, 389Bernoulli, Daniel, 173Bernoulli’s principle, 173,

173–177, 748beta particles, 400, 400, 401,

402bicycles, 226big bang theory, 19bilirubin, 562bimetallic strips, 250, 250binary numbers, 490biochemicals, 384–387biochemistry, 384–387biology, 9biomass, 236, 237birds, 175, 460bits, 497black holes, 127bleach, 48, 48

Index


Index 777

IND

EX

block and tackle, 203–204, 204blood, 96

pH of, 381blood pressure, 162body temperature, 248Bohr, Niels, 286boiling, 70, 70boiling point, 70–71, 73

pressure and, 71bonds. See chemical bondsbooming sands, 532, 532, 542boric acid, 372boron, 291, 307Boron group, 314botany, 9Boyle, Robert, 2, 65Boyle’s law, 65, 65, 747brake fluid, 62brakes, 167, 167branched chain structures, 383breaker boxes, 444–445breathing, 166, 166bridges

collapse of, 525, 525Golden Gate (San Francisco),

117, 135, 135bromine, 309, 316bubbles, 163, 163buckyballs, 323, 323buoyant force, 168–172bytes, 497

Ccalcium, 311

in bones, 40calcium carbonate, 382, 394calcium hydroxide, 379calcium phosphate, 86calcium sulfate, 382calories, 258, 262calorimeters, 258, 258, 262, 271cameras, 608, 608carbohydrates, 384

simple and complex, 384carbon

beta decay, 400, 400bonding, 323, 324, 383, 383carbon-14 dating, 403–404compounds of, 315, 346,

346, 383, 383–389

electron-dot diagrams, 337, 337

isotopes, 292carbonated drinks, 88, 88carbon dioxide

composition of, 86gas formation and, 350, 351properties of, 355sublimation, 72, 72

Carbon group, 314–315carbonic acid, 88, 378carbon monoxide, 86, 355careers, 10, 10

arson investigator, 371electronics engineer, 32experimental physicist, 299mechanical engineer, 159power-plant manager, 243

carsair bags, 348batteries, 431brake fluid, 62coolants, 123crash tests, 146, 348energy conversions in, 227engines, 267, 267fuel combustion, 350hydraulic brakes, 62, 167, 167maintenance of, 47, 47mass production, 185motor oil, 197painting, 423pollution from, 148side mirrors, 602spoilers, 176tires, 124, 162

Cassini spacecraft, 396, 396catalysts, 365catalytic converters, 365cathode-ray tubes (CRT), 282,

282, 493Cavendish, Henry, 3CD players, 419, 419, 490,

490–491, 491CDs (compact discs), 490,

490–491cell diagrams, 20cell membranes, 385, 385–386cells, electric, 430, 430–431Celsius scale, 26, 26, 248, 249,

730central processing unit (CPU),

496, 496

centrifuges, 91centripetal acceleration, 114centripetal force, 142, 142cerium sulfate, 95Chadwick, James, 276chain reactions, 325, 407,

407–408changes of state, 68–73, 261

boiling, 70chart, 72condensation, 71defined, 68, 68endothermic, 69evaporation, 70exothermic, 69freezing, 69, 69graph of, 73melting, 69, 69sublimation, 72temperature and, 73vaporization, 70, 70

characteristic properties, 48, 69–70, 83

charge. See electric chargeCharles’s law, 66, 747chemical bonding, 328–341chemical bonds, 328. See also

compoundscovalent, 336–339defined, 328double, 388, 388ionic, 332–335making and breaking, 352,

352metallic, 339–341, 340, 341triple, 388, 388

chemical changes, 49–51, 262clues to, 50, 50–51

chemical energyin chemical reactions, 351,

361, 361–363, 363conversions, 223, 223–224,

224, 226, 227overview, 218, 219

chemical equations, 354–357, 356, 743

chemical formulas, 352,352–353, 353, 355

chemical properties, 47–49chemical reactions, 348–365,

743energy and, 361, 361–363,

363


Index778

IND

EX

equations for, 354–357, 356overview, 350–352rates of, 363–365types of, 358–360

chemical symbols, 308, 354–355chemistry, 8Chernobyl nuclear accident,

409, 409, 411chloride ion, 334, 334chlorine

atoms, 329, 334, 334bleach, 351hydrogen and, 352properties of, 87, 316

chlorophyll, 224, 350, 585cholesterol, 385circle graph, 735circuit boards, 482, 482circuit breakers, 444–445, 445circuits, 440–445. See also

electric circuitsintegrated, 486, 486

citric acid, 378closed systems, 230, 230–231coal, 184, 232, 232–233cobalt, 83, 355coefficients, 356Coleman, Bessie, 104, 104colloids, 97, 97, 99color, 43, 351, 572, 577–578,

578, 582–585, 584, 585.See also light

mixing of, 584, 584–585, 585of objects, 582–583, 583separation, 578, 578

color deficiency, 607, 607combustion, 266, 371comets, 71, 298

Halley’s, 104communication technology

analog signals, 488–490, 489, 490, 492

CDs (compact discs), 490, 490digital signals, 490, 490–491,

491radio, 492, 492records, 490, 490telegraph, 488, 488telephone, 489, 489television, 493, 493

commutator, 466, 466compasses, 459, 460, 460,

462, 463

compound machines, 204–205compounds

breakdown of, 88, 88covalent, 336–339, 337, 338,

353, 353, 375–376defined, 86, 743formation of, 83, 86, 86, 743ionic, 335, 335, 353, 353,

374, 374–375, 375in nature, 89, 89organic, 383, 383–389properties of, 87

compression, 135, 514, 514,534, 535

compressors, 268, 268computers, 494–499

basic functions, 494, 494defined, 494hardware, 496, 496–497, 497history, 495Internet, 499, 499software, 498, 498

concave lenses, 604, 604, 606concave mirrors, 600, 600–601,

601concentration, 94, 364

calculation of, 94, 749concept mapping

defined, 728condensation, 68, 71–72condensation point, 71conduction

of charge, 425, 425, 435of electric current, 375,

375–377, 376, 379of thermal energy, 253,

253–254conductivity

electrical, 306–307, 375,375–377, 376, 379

thermal, 44, 306–307conductors, 254, 375, 377,

379, 427conservation

of charge, 425, 446of energy, 19, 229, 229–231,

362of mass, 357, 357of momentum, 152,

152–153, 153constructive interference, 523,

523–524, 524, 579, 580contact lenses, 347, 347

control group, 15, 733controlled experiment, 15, 733convection, 254, 254convection currents, 254conversion tables

SI, 729temperature, 730

convex lenses, 603, 603–604, 606

convex mirrors, 602, 602cooling systems, 267–268, 268,

271copper, 256, 292, 292, 306, 322

density of, 45copper carbonate, 50cornea, 605, 605corrosivity, 377, 379covalent bonds, 336–339, 337,

338covalent compounds

formulas for, 353, 353organic compounds, 383,

383–389, 388, 389properties of, 375–376, 376

CPU (central processing unit), 496, 496

crest, 513CRT (cathode-ray tube), 282,

282, 493cryogenics, 274crystal lattice, 335. See also

ionic bondscrystalline solids, 61, 61, 335,

374, 374Curie, Irene, 401Curie, Marie, 325, 325, 398,

401Curie, Pierre, 325current, 433. See also amperes;

electric currentCzarnowski, James, 4, 12,

12–17

DDallos, Joseph, 347Dalton, John, 277, 281, 281–283dark matter, 56data, 16deafness, 538deceleration, 113

Index 779

IND

EX

decibels, 543decimals, 739decomposition reactions, 359,

359Deep Flight, 160Democritus, 276, 276, 280–281density

buoyant force and, 170–171calculation of, 27, 45, 170, 749defined, 27, 44–45, 53, 749identifying substances using,

45liquid layers and, 46, 46of pennies, 45units, 27water pressure and, 165

deoxyribonucleic acid (DNA), 387, 387, 394

derived quantities, 26–27destructive interference, 523,

523, 524, 580, 580diamond, 315DiAPLEX®, 275, 275diatomic molecules, 338,

338–339Diegert, Carl, 560diffraction, 521–522, 522, 551,

551, 579, 579diffuse reflection, 576, 576digital signals, 490, 490–491,

491dimension, 38dinosaurs, 278, 560diodes, 484, 484direct current (DC), 434, 434,

484dissolution, 92, 95, 375–376distillation, 91DNA (deoxyribonucleic acid),

387, 387, 394domains, 456–458, 457doorbells, 465, 465doping, 483Doppler effect, 506, 542, 542double-replacement reactions,

360, 360drag, 158, 176drums, 554, 554dry cells, 431dry ice, 72, 72. See also

carbon dioxideductility, 44, 85, 306, 340dynamite, 325

EE. coli, 395, 590ears, 504, 537, 561. See also

hearingEarth

core, 460gravity and, 126–129, 128magnetic field, 459, 459,

460–461rotational velocity, 111rotation of, 22

earthquakes, 489, 508, 515Earthships, 244, 244–245, 264echoes, 520, 545, 545echolocation, 546, 546–547ecology, 9effervescent tablets, 50efficiency

energy, 12–13, 13, 16, 16,228

mechanical, 197, 205Egypt, 186Einstein, Albert, 33, 104, 104,

507, 565, 565Einthoven, Willem, 419, 419elastic force, 135electrical energy

alternative sources of, 432atoms and, 422–423from chemical reactions, 361electric charge and, 282–283,

422–429, 446from fossil fuels, 234, 234,

237generating, 471, 473, 473household use of, 219, 219,

225, 225measurement of, 438–439,

447nuclear fission and, 235,

408, 408–409nuclear fusion and, 410,

410–411, 411power plants and, 243, 243resistance and, 435–437, 447from water, 235, 235from wind, 228, 228, 236, 236

electrical storms, 428, 428–429,446

electric cells, 430, 430–431electric charge, 282, 423–427

conduction, 425

conservation of, 425detecting, 426friction and, 424, 424induction, 425law of, 423, 423static electricity and, 427, 427

electric circuits, 440–445defined, 440failures, 444, 444–445, 445,

447household, 444–445parts of, 440, 440–441, 441,

447types of, 441–443, 442, 443,

446electric current, 430–431,

433–439, 447alternating, 434, 434,

471–472, 484covalent compounds and,

376, 376diodes and, 484direct, 434, 434, 484ionic compounds and, 375,

375magnetic force and, 465,

465, 466, 466–467, 467, 468, 468–470, 469, 470

transistors, 485, 485–486, 486electric discharge, 428electric eels, 420, 435electric fields, 423, 433electric force, 423, 446electric generators, 234, 234,

470, 470–471, 471electricity, 418, 420. See also

electrical energy;electric current

from magnetism, 419, 468–473

from ocean temperature differences, 266

electric motors, 466, 466electric power, 437–438, 447.

See also electrical energyelectrocardiograph machine,

419electrodes, 430, 430electrolysis, 88, 359electrolytes, 430electromagnetic force, 293electromagnetic induction, 469,

469, 470, 470



Index780

IND

EX

applications, 470, 470–473, 471, 472, 473

electromagnetic spectrum, 567–574, 568–569.See also light

electromagnetic wave, 255, 255,564, 564

electromagnetism, 452–479. See also magnets

applications, 465–467discovery of, 462, 462–463electric current and, 465,

465, 466, 466, 467, 467, 468, 468–470, 469, 470

light waves, 564, 564–565, 567

uses of, 463–467electromagnets, 458, 464electron clouds, 286, 286, 742,

742electron-dot diagrams, 337electronic components,

482–487circuit boards, 482, 482diodes, 484, 484integrated circuits, 486, 486,

500semiconductors and, 483,

483transistors, 485, 485–486,

486, 500vacuum tubes, 487, 487

electronsin atomic models, 283, 283,

285, 285–286, 286, 742chemical bonding and,

328–331discovery of, 277, 283electrical energy and, 219,

219, 422, 433, 433in electric cells, 430electric charge, 423–427,

425, 426in energy levels, 329, 329magnetic fields and, 456in metals, 340, 340–341, 341overview, 283, 288, 289valence, 329, 329–331, 330,

331electroscopes, 426, 426elements, 82–85. See also

periodic table

chemical symbols for, 308, 354–355

classes of, 84, 85, 98, 306–307defined, 82, 742groups of, 310–317pattern of arrangement, 83,

302–309elephants, 300, 300, 531, 531endothermic, 69, 362endothermic reactions, 69, 72,

362–363, 363energy, 212–237. See also

chemical energy; electrical energy; gravitational potential energy; kinetic energy; mechanical energy; nuclear energy; thermal energy

change of state and, 68conservation of, 19, 229,

229–231, 230, 362conversions, 222, 222–228,

223, 228, 234defined, 7, 214diagrams, 363efficiency, 12–13, 13, 16, 228electron loss/gain and,

333–334in food, 262light, 220, 220nonrenewable resources,

232, 232–235, 237renewable resources, 235,

235–236, 236, 237, 432resources, 232–237sound, 220, 220transfer of, 257units, 214in waves, 510–512, 517–518work and, 214, 214–217

engines, 266, 266–267, 267ENIAC (Electronic Numerical

Integrator and Computer), 495, 495

enzymes, 365, 386equations, 354–357, 356Erie, Lake, 37Escherichia coli, 395, 590esters, 389ethene, 388ethyne, 388europium, 313

evaporation, 70, 70exothermic, 69, 361exothermic reactions, 69, 71,

361, 361, 363experimental group, 733external combustion engines,

266, 266eyes, 605, 605–607, 606

FFahrenheit scale, 26, 26, 248,

249, 728falling objects

acceleration of, 138–139free fall, 141, 141–142Newton’s second law and,

149orbits, 141–142, 142projectile motion, 143,

143–144, 144terminal velocity, 140

Faraday, Michael, 468–470, 474farsightedness, 606, 606fats, dietary, 385Feinbloom, William, 347ferromagnets, 458fertilizers, 89, 315fiber optics, 612fields

electric, 423electromagnetic waves and,

564magnetic, 456, 456, 457,

463, 469Fields, Julie, 10filtration, 91, 96fireflies, 590fire retardant, 370, 370fireworks, 322, 322first class lever, 198, 198.

See also leversfish, swim bladders in, 172, 172fission, 221, 221, 235, 237, 406,

406–411, 410fixed pulley, 203, 203flammability, 47flashbulbs, 357, 358Fleming, Alexander, 3floating (buoyant force),

168–172

Index 781

IND

EX

fluid friction, 122fluids, 122, 160–177. See also

gases; liquidsBernoulli’s principle, 173,

173–177buoyant force, 168–172defined, 162drag, 176flow, 166pressure, 162–167turbulence, 176

fluorescence, 398, 398, 614, 617

fluorescent light, 596, 596fluorine, 338focal length, 600, 601focal point, 600, 602, 603fool’s gold (iron pyrite), 34,

34–35, density of, 45

forceacceleration and, 148,

148–149action/reaction pairs, 150,

150–151, 151, 153, 153in atoms, 293balanced, 117–118buoyant, 168–172centripetal, 142defined, 115distance and, 194, 195electric, 423, 446electromagnetic, 293friction, 119–124, 120gravitational, 39, 39–40,

125–129input, 193, 193–194, 194,

195, 196, 196magnetic, 455, 455motion and, 117–118net, 116, 116–117, 117, 748output, 193, 193, 195, 196,

196strong/weak, 293, 402unbalanced, 117–118units, 41, 115work and, 188–190, 189, 190

fossil fuels, 51, 232, 232–234, 233, 234, 237

fractions, 739–740Franklin, Benjamin, 418, 418,

428–429Franklin, Melissa, 284, 299, 299

Franscioni, Warren, 182free fall, 141, 141–142. See also

projectile motionfreezing, 68, 69, 72freezing point, 69frequency, 518

of light, 567–574of sound, 540–541, 541

frequency modulation (FM), 568–569, 569

friction, 119–124as activation energy, 362defined, 119effects of, 123, 123–124efficiency and, 197electric charge and, 424, 424energy conservation and, 229force and, 120, 120–122Newton’s first law and, 146resistance and, 435sources of, 119–120types of, 121–122

fuelsfossil, 51, 232, 232–234, 233,

234, 237hydrogen gas, 317, 355uranium, 235

fulcrum, 198fulgurite, 58, 58Fuller, Buckminster, 323.

See also buckyballfuses, 445, 445fusion, nuclear, 221, 410–411

GGalileo Galilei, 138, 506gallium, 69, 69galvanometers, 467, 467gamma rays, 400, 401, 402,

569, 569, 574gases

formation of, 351as lubricants, 123model of, 60natural, 232, 232, 233pressure of, 64–66, 74in solution, 93states of matter and, 260,

262volume of, 38, 63, 63, 65–66

gas hydrates, 212, 212gas laws

Boyle’s law, 65, 65Charles’s law, 66, 66

gas masks, 618Geim, Andrey, 452General Electric, 372generators, 234, 234, 470,

470–471, 471geology, 9geomagnetic storms, 478geothermal energy, 236, 237germanium, 303, 309, 314geysers, 236GFCI (ground fault circuit

interrupters), 445, 445Gilbert, William, 459glass, 256glass making, 59gliders, 175glucose, 352, 362, 384Goddard, Robert, 184, 184gold, 34, 34–35, 93, 277, 312,

312, 340density of, 45specific heat capacity of, 256

Golden Gate Bridge, 117, 135, 135

gold foil experiment, 284,284–285

graduated cylinders, 25, 25, 37, 731

grams, 24, 26, 41granite, 90, 92graphite, 123graphs, 16, 16, 66, 109, 114,

233, 735–737gravitational force, 125–129gravitational potential energy,

216, 216–217gravity, 125–129

acceleration due to, 138–139, 139, 144, 144,149

air resistance and, 139–141within atoms, 293defined, 39, 125distance and, 127, 128, 128on Earth, 126–129law of universal gravitation,

105, 126–128, 127, 746mass and, 39, 39–40, 127,

127–129, 129


Index782

IND

EX

matter and, 56, 125orbits and, 141–142, 142projectile motion and, 143,

143–144, 144terminal velocity and, 140

Great Pyramid of Giza (Egypt), 186, 186, 200

green buildings, 242greenhouse effect, 255, 255ground fault circuit interrupters

(GFCI), 445, 445groups, elements in, 309–317,

330, 742

Hhalf-life

carbon-14 dating, 403–404, 404

examples of, 404halogen lights, 595, 595halogens, 316, 334headphones, 504, 538health

food contamination, 590hearing problems, 504, 538,

555jaundice, 562kidney stones, 541leukemia, 401magnets in, 479radiation in medicine, 405,

574radiation sickness, 401–402ultrasound, 547, 547vision problems, 606,

606–607, 607vitamin D, 573X rays, 574, 574

hearing, 504, 537, 538, 541, 541, 555

heat, 251–259, 361. See alsotemperature; thermal conductivity; thermal energy

calculation of, 257changes of state and, 261chemical changes and, 262cooling systems, 267–268,

268heating methods, 253–255

heating systems, 263,263–265, 264, 265

specific heat capacity, 256–258

thermal energy and, 259thermal pollution, 269

heat engines, 266, 266–267, 267

heat island effect, 269Heisenberg, Werner, 286helium

from alpha decay, 399, 399density of, 45from nuclear fusion, 410properties of, 45, 48, 48,

170, 170uses of, 317, 317valence electrons, 330–331

hemoglobin, 386Henry, Joseph, 468Hensler, Mike, 211, 211Hero, 60hertz, 518heterogeneous mixtures, 96Hindenburg, 3, 3Hodgson, Peter, 372holograms, 506, 506, 611, 611homogeneous mixtures, 92Hopper, Grace Murray, 418, 418hormones, 386hot-water heating, 263, 263household appliances, 438–439household circuits, 444–445Hubble, Edwin, 506Huygens, Christiaan, 185hydraulic devices, 167, 167hydrocarbons, 388–389hydrochloric acid, 351, 377,

377–378hydroelectricity, 235, 471, 471hydrogen. See also nuclear

fusionchlorine and, 352electron-dot diagrams, 337gas, 355, 364, 377isotopes, 289, 289–290, 290,

292molecules, 336, 336nuclear fusion, 410, 410–411properties of, 317radioactive isotope, 403, 404

hydrogen peroxide, 86, 88, 363hypotheses, 14–17, 22

Iideal machine, 197illuminated objects, 594.

See also lightincandescent light, 595, 595incidence, angle of, 575, 747inclined planes, 186, 200, 200induction, 419, 425, 425, 469,

469–473, 475inertia, 42, 52, 147, 147, 149infrared waves, 255, 255, 346,

568, 571, 571infrasonic frequencies, 531, 541infrasound, 531inhibitors, 365inner ear, 537input devices, 496, 496–497input force, 193. See also force

distance and, 194, 194, 195inclined planes and, 200,

200levers and, 198, 198–199,

199mechanical advantage and,

196, 196pulleys and, 203, 203–204,

204screws and, 201, 201wedges and, 201, 201wheel and axle and, 202, 202

insulation, thermal, 244insulators, electric, 427, 435insulators, thermal, 254insulin, 386integrated circuits, 418, 486,

486interference, 522, 522–525,

548, 548–550, 579–580, 580

internal combustion engines, 267, 267

International System of Units, 24–26

conversion chart, 729SI prefixes, 729

Internet, 499, 499iodine, 316, 316ionic bonds, 332–335ionic compounds, 335, 353,

353, 374, 374–375, 375ions, 289, 332–335, 333, 334,

340–341, 341, 743


Index 783

IND

EX

iris, 605iron, 47, 47–48, 83, 256, 312,

312iron pyrite, 34, 34–35

density of, 45isotopes, 290, 290–292, 291,

400, 403

JJackson, Shirley Ann, 10jaundice, 562joules, 190, 214Joyce, James, 276jumping beans, 152

KKekulé, Friedrich August, 324Kelvin scale, 26, 248, 249, 730Kemph, Martine, 211kidney stones, 541kilocalories, 258, 262kilograms, 24, 26, 41kilowatt-hours, 439kilowatts, 437–439kinetic energy

calculation of, 215conversions, 222, 222, 223,

223, 225–230, 234machines and, 226, 227mass and, 215, 215mechanical energy and, 217potential energy and, 222,

222–223, 223speed and, 215, 215thermal energy and, 218, 218

King, Martin Luther, Jr., 324knife, as wedge, 201Kodiak Island, 508krypton, 83, 277, 337, 406

LLake Erie, volume of, 37lanthanides, 313La Paz, Bolivia, 164lasers, 32, 78, 274, 506

in CD players, 491, 491in holograms, 611, 611operation of, 609–610, 610retroreflectors and, 592, 592

Lavoisier, Antoine, 357law, scientific, 19law of conservation of energy,

19, 230, 230–231, 362, 746

law of conservation of mass, 357, 357

law of conservation of momen-tum, 152, 152–153, 153

law of electric charges, 423, 423law of reflection, 575, 575, 746law of universal gravitation,

105, 126–128, 127, 746lead, 256, 308

density of, 45LED (light-emitting diode), 482length, 24–25lenses, 603, 603–604, 604,

605, 606, 608leukemia, 401levers, 186, 198, 198–199, 199Lidar, 32lift, 174, 182light. See also lasers;

light bulbs; wavesabsorption and scattering,

576, 576–577from chemical reactions, 351,

361coherent, 609colors, 572, 577–578, 578,

581–584, 584diffraction, 579, 579energy, 220, 220, 224fiber optics, 612fluorescent, 596, 596frequencies of, 567–574infrared, 346, 482, 568, 571,

571matter and, 581–582neon, 317, 596, 596

optical instruments, 608,608–609, 609

polarized, 612–613, 613pollution, 619production of, 565rays, 598, 598, 600scattering, 93, 93, 96sight and, 575, 605,

605–607, 606speed of, 506–507, 566, 567,

577transmission of, 581ultraviolet, 346, 569, 573visible, 569, 572waves, 512, 521, 564,

567–574light bulbs

argon in, 291, 317in circuits, 442, 442–443,

443energy conservation in, 225,

230, 230tungsten filaments in, 435types of, 595, 596, 596–597,

597light-emitting diode (LED), 482lightning, 78, 418, 428,

428–429, 429, 446, 451, 551, 566

lightning rods, 429, 429, 446Lim, Drahoslav, 347line graphs, 736, 736lipids, 385, 385liquids. See also fluids

density of, 46, 46model of, 60particles in, 62, 62–63in solutions, 93states of matter and, 260surface tension and viscosity,

63, 63volume of, 25, 37, 37

liters, 24, 25litmus paper, 378, 378–379,

379loads, 440, 440longitudinal waves, 514,

514–515, 517, 535, 535loudness, 542–544lubricants, 123luminous objects, 594, 614.

See also light


Index784

IND

EX

MMaan, Jan, 452machines, 192–205

compound, 204–205defined, 192energy and, 226, 226–227,

227ideal, 197mechanical advantage, 196,

196, 198–204mechanical efficiency, 197,

205simple, 198–204work and, 193–194, 195

MACHOs (MAssive Compact Halo Objects), 56

Magellan, Ferdinand, 105maglev trains, 464magnesium, 86, 311, 322, 331,

357, 358magnesium oxide, 358, 375magnetic fields, 456, 456magnetic force, 455, 455magnetic resonance imaging

(MRI), 479magnetic resonance

spectroscopy (MRS), 479magnetism, electricity from,

468–473magnetite, 454, 458, 458, 460magnetrons, 591magnets, 91, 436. See also

electromagnetismatomic, 452in cows, 456cut in half, 458, 458domains in, 456–457, 457Earth as, 459, 459–461, 460electromagnets, 458, 464magnetic materials, 456–458,

457properties of, 454, 454–456,

456types of, 458–459uses of, 463–464

magnifying glasses, 603malachite, 585malleability, 44, 85, 306–307,

340marimba, 524Marshall, James, 277

massacceleration and, 148–149,

149atomic, 292, 302–303conservation of, 357, 357defined, 26, 38, 41gravity and, 127, 127–129,

129heat and, 257inertia and, 42, 147kinetic energy and, 215measurement of, 41, 41number, 291, 291–292,

399–400units, 24, 26weight and, 39–41, 41, 129,

129Massachusetts Institute of

Technology (MIT), 4, 12mass number, 291, 291–292,

399–400matches, 315, 362, 362math refresher, 738–741matter, 2, 36–51

defined, 7, 36, 742effects of radiation on,

401–402energy from, 407, 407, 410gravity and, 125–126light and, 581–582overview, 36–42properties of, 43–51states of, 58–73, 260, 261volume of, 36–38

McKee, Larry, 371, 371measurement units, 24–27, 729measuring skills, 731mechanical advantage, 196,

196, 198–204calculation of, 196

mechanical efficiency, 197, 205calculation of, 197compound machines and,

205mechanical energy, 217, 217,

226, 226–227, 227medicines, 96medium, 511, 577

sound and, 536, 539–540Mele, Cheryl, 243, 243melting, 49, 49, 68, 69, 72melting point, 69, 73, 375,

375–376

memory, computer, 497Mendeleev, Dmitri, 277, 300,

302, 302–303meniscus, 37, 37mercury, 70, 88, 256, 312

density of, 45mercury(II) oxide, 88metallic bonds, 339–341, 340,

341metalloids, 84–85, 307,

314–315metals

alkali, 310–311alkaline-earth, 311as conductors, 306, 340, 427properties of, 84–85, 306,

306, 340–341, 341transition, 312–313

meteorites, 82, 325, 325meteorology, 9meters, 24, 25meterstick, 731methane, 77, 262micromachine, 210, 210microprocessors, 419, 495, 495microscopes, 609

scanning tunneling, 277microwave ovens, 570, 591microwaves, 220, 568, 570–571middle ear, 537milk, 50, 385mirrors, 593, 599, 599–602,

600, 601, 602mixtures, 90–97

colloids, 97, 97heterogeneous, 96homogenous, 92properties of, 90–93separation of, 91, 96solutions, 92–95suspensions, 96

modelsatomic theory, 280–286, 283,

285–286defined, 20Earth, sun, moon, 22electron-dot diagrams, 337,

337electrons, 283, 283, 286, 286overview, 20, 20–23size of, 22of solids, liquids, and gases,

60


Index 785

IND

EX

space-filling, 338, 339structural formulas, 383theories and, 23

modems, 497modulation of radio waves,

568–569, 569, 570molecules, 336–339, 337, 338,

743momentum, 152, 152–153, 153monopoles, 458moon

distance to Earth, 592gravity and, 125, 125motion of, 22, 142

Morgan, Garrett, 618Morrison, Fred, 182Morse code, 488, 488Moseley, Henry, 303motion

circular, 114forces and, 117–118inertia, 147measuring, 108–114Newton’s first law and,

145–147Newton’s second law and,

148–149Newton’s third law and,

150–151, 153observing, 108pendulum, 223, 223perpetual, 231, 231projectile, 143, 143–144, 144reference points, 108

motors, electric, 466, 466movable pulley, 203, 203Mozart, Wolfgang Amadeus,

105, 105music, 555, 555musical instruments, 552,

552–554, 553, 554

NNapoleon, 200Napoleon III, 314NASA, 32, 105, 136natural gas, 212, 232, 232, 233,

262nearsightedness, 606, 606negative acceleration, 113

neon, 277, 317neon light, 596, 596–597neutralization, 380–381, 381, 382neutrons, 246, 276, 288,

288–293, 290, 403, 406,406–408, 742

neutron spectrometer, 298Newcomen, Thomas, 2, 79Newton, Sir Isaac, 105, 126,

126, 145, 507newtons, 41, 115, 128Newton’s first law of motion,

145–147, 746Newton’s second law of

motion, 148–149, 746Newton’s third law of motion,

150–151, 153, 746action force, 150reaction force, 150

nickel, 83nickel(II) oxide, 375Nimbus III, 324nitric acid, 378nitrogen, 89, 315nitrogen-fixing bacteria, 89Nitrogen group, 315nitroglycerin, 325Nobel, Alfred, 325noble gases, 316–317, 330noise, 555, 555noise pollution, 555nonmetals, 84–85

properties of, 307, 307,316–317

nonrenewable resources, 232–235

normal, 575, 575, 747n-type semiconductor, 483, 483nuclear energy, 221, 221, 235,

237, 406, 406–411, 410nuclear fission, 221, 235, 406,

406–409, 407nuclear fusion, 221, 410,

410–411nuclear magnetic resonance

(NMR), 395nuclear power, 408, 408–409nuclear radiation, 398–402, 401nuclear waste, 409, 411, 416,

416nucleic acids, 387, 387nucleus, 285, 285, 286, 286,

288, 402–403, 742

Oobservations, 12oceanography, 9ocean thermal energy

conversion (OTEC), 266ocean waves, 515odor, 43Oersted, Hans Christian,

462–463Ohm, Georg, 437ohms (units), 435, 437Ohm’s law, 437, 446–447Okamoto, Steve, 159, 159opaque materials, 582,

582–583optical axis, 600, 600, 601, 602,

603optical fibers, 612, 612optical illusions, 578orbits, 141–142, 142organic compounds, 325, 383,

383–389, 388, 389biochemicals, 384–387carbohydrates, 384lipids, 385nucleic acids, 387, 387proteins, 386

Orion, 346oscilloscopes, 544, 544, 552,

555outer ear, 537output devices, 496–497, 497output force, 193. See also

forcedistance and, 194, 194–195,

195inclined planes and, 200, 200levers and, 198, 198–199,

199mechanical advantage and,

196, 196pulleys and, 203, 203–204,

204screws and, 201, 201–202,

202wedges and, 201, 201wheel and axle and, 202,

202, 203overtones, 550, 552, 552oxide ion, 334, 334oxygen

atoms, 329, 334, 334


Index786

IND

EX

chemical formula, 352density of, 45electron-dot diagrams, 337in light bulbs, 291properties of, 291, 315

Oxygen group, 315

Ppacemaker cells, 435Papin, Denis, 79parachutes, 140parallel circuits, 443, 443, 446Parasaurolophus, 560particle accelerators, 299particles

alpha, 399, 399beta, 400, 400light as, 565light scattering, 93, 93, 96in solution, 93states of matter and, 60, 61in waves, 513–515

Pascal, Blaise, 167pascals, 71, 162Pascal’s principle, 167, 747passive solar heating, 265, 265Pasteur, Louis, 346pendulum motion, 15, 223, 223penguins, 4, 4, 14, 14pennies, 45, 287percentages, 739percussion instruments, 554, 554period, 309, 309, 742periodic, 302periodic law, 303periodic table, 304–305,

744–745classes, 306–308development of, 277,

302–303groups, 309periods, 309valence electrons and, 330,

330–331periods of elements, 309perpendicular, defined, 513perpetual motion machines,

231perspiration, 70petroleum, 232, 232, 233

pH, 380, 380–381, 381, 743values, 380, 380

phospholipids, 385, 385phosphor, 569phosphorus, 315, 415photocell, 432. See also solar

energyphotons, 565photosynthesis, 224, 224, 262,

362, 572physical changes, 48–49, 261physical properties, 43–46physical science, 6–8, 9, 10physics, 8pigments, 584–585. See also

colorpitch, 540–542plane mirrors, 599, 599plasma (blood), 96plasma channel, 78plasmas, 60, 67, 67, 410plum-pudding model, 283, 283plutonium, 396polarized light, 612, 612–613,

613poles, magnetic, 454–456, 455,

456, 459, 459–460pollution

noise, 555thermal, 269

Polo, Marco, 532polonium, 402, 402polymerase chain reaction

(PCR), 394polymers, 347positive acceleration, 113, 114potassium bromide, 95, 311potential difference (voltage),

431, 431, 434–435, 437potential energy, 216, 216–217,

222, 222–223calculation of, 217conversions involving, 222,

222, 223, 223, 229, 229power, 191, 437–438, 749

calculating, 191hydroelectric, 471, 471nuclear, 408, 408–409

power plants, 269precipitates, 351. See also

solidsprefixes, 353, 353

SI, 729

pressure, 162, 162, 749atmospheric, 71, 163,

163–164, 164, 166boiling point and, 71calculation of, 162depth and, 164–165fluids and, 162, 162–167, 173gases and, 64–66Pascal’s principle, 167, 747units, 71, 162water, 165, 165

primary colors, 584, 584products, 354, 354, 356. See

also chemical reactionsprojectile motion, 143,

143–144, 144propane, 388, 388propellers, 13properties

characteristic, 69–70, 83chemical, 47–49, 53of matter, 43–51physical, 43–46

proportions, defined, 738propulsion systems, 4, 12–17proteins, 339, 346, 386, 395Proteus (boat), 4, 4, 12, 15,

16–17, 22–23protons

discovery of, 284electric charge, 423, 742nuclear decay and, 402–403overview, 288, 288, 290, 422

p-type semiconductor, 483, 483pulleys, 203, 203–204, 204pupil, 605pure substance, 82pyrotechnics, 322, 322

Qquarks, 276, 299

Rradar, 571, 571radiation, 255, 565radiation sickness, 401–402radioactive decay, 399–404


Index 787

IND

EX

radioactivity, 291, 313, 325, 398–405. See also nuclearradiation

alpha particles, 399, 399, 401, 401–402

atomic nucleus and, 402–403

beta particles, 400, 400–402, 401

carbon-14 dating, 403–405discovery of, 398gamma rays, 400–402, 401,

569, 574penetrating power of, 401,

401–402stainless steel and, 417types of decay, 399–400uses of, 396, 405

radio broadcasting, 492, 492radioisotope thermoelectric

generator (RTG), 396, 396radios, 487, 487radio waves, 492, 492, 536,

568, 568–570, 569radium, 399, 399radius, 203, 203radon, 399, 399, 402rainbows, 578RAM (random-access memory),

496, 497ramps, 194, 194, 200, 200Ramsay, William, 277rarefaction, 514, 514, 534, 535ratios

defined, 738ray diagrams, 600, 600–604,

601, 602, 603, 604reactants, 354, 354, 356. See

also chemical reactionsreaction force, 150, 150, 151reactivity, 47real images, 600–601, 601,

604, 604record players, 490, 490reducing fractions, 739reference points, 108, 108reflected beam, 747reflection, 520, 520, 545,

545–547, 575, 575–576, 576, 599, 602, 612

refraction, 521, 521, 577,577–578, 578, 603, 603–604, 604

refrigerators, 268, 268remote controls, 482, 482renewable resources, 235,

235–236, 236resistance, 435–437, 447resonance, 524–525, 550resonant frequencies, 550, 550resultant velocity, 111, 111retina, 605retroreflector, 592, 592Reynolds, Michael, 244ring structures, 383RNA (ribonucleic acid), 387rocket, 184roller coasters, 8, 159, 159, 229,

229rolling friction, 121, 121ROM (read-only memory), 497rubber, 372rust, 47, 47Rutan, Richard, 326Rutherford, Ernest, 276, 284–285

Ssafety

acids and, 377bases and, 379electrical, 444, 445guidelines, 622symbols, 27, 27, 622, 622

Salmonella, 590salt. See sodium chloridesalts, 382, 382sampling rates, 491Sand Mountain, 542sands, booming, 532, 542Santibanez, Roberto, 10saturated hydrocarbons, 388,

388saturation in solutions, 94Sauerbrun, Karl von Drais de,

185Savery, Thomas, 79scattering, 576, 576–577Schrödinger, Erwin, 286science, 6

branches of, 9, 9careers in, 10models in, 20–23technology and, 11

scientific knowledge, 18–19, 22–23

scientific method, 11–19, 18,22–23, 732–734

scientific notation, 741screws, 201, 201–202, 202Seawise Giant, 171second class lever, 199, 199.

See also leversseeds, gravity and, 125seismographs, 489semiconductors, 307, 483, 483separation techniques, 91, 96series circuits, 442, 442,

446–447short circuit, 444SI (Système International

d’Unités), 24conversion chart, 729prefixes, 729units, 24, 24–26

sight, 575, 605, 605–607, 606signals

analog, 489, 489–490, 490,492

audio, 493, 493defined, 488digital, 490, 490–491, 491television, 570, 584video, 493, 493

silica, 58silicon, 307, 314, 483, 483Silly Putty, 2, 2, 372, 372silver

density of, 45specific heat capacity of, 256

simple machines, 198–203in compound machines,

204–205mechanical advantage of,

198–203types of, 198–203

single-replacement reactions, 359, 359–360, 360

sky glow, 619sliding friction, 121, 121slope, 736sodium, 87, 329, 333, 333sodium chlorate, 95sodium chloride

crystal lattices, 22, 335, 335properties of, 69, 87, 95, 311,

332


Index788

IND

EX

salt water, 92synthesis, 87, 358uses of, 382

sodium hydroxide, 311, 379sodium nitrate, 95, 382sodium vapor lights, 597, 597solar cells, 235, 235solar energy, 235, 237, 432solar flares, 478solar heating, 265, 265solar wind, 478solenoids, 452, 463, 463–465,

464, 465solids. See also compounds

formation of, 351model of, 60particles in, 60in solutions, 93states of matter and, 260types of, 61, 61volume of, 25, 37–38, 38

solubility, 44, 94–95, 95,375–376

solutes, 92, 94solutions, 92–95. See also

dissolution; liquids; solubility

solvents, 92sonar, 546, 546–547sonic booms, 549, 549sound. See also waves

amplitude, 542–544, 544detecting, 535–536, 537diffraction, 551, 551frequency, 540, 540–541,

541, 544interference, 548, 548–550loudness, 542–544, 544pitch, 540, 540–541, 541,

544production of, 534, 534–535quality, 552–555reflection of, 545, 545–547resonance, 550resonant frequencies, 550,

550speed of, 104, 507, 519,

539–540waves, 21, 21, 511, 515, 515,

520, 535, 535, 549–550sound barrier, 540, 548,

548–549, 549sound energy, 220

spacecraft, exploratory, 396, 396space shuttle, 50, 111, 136,

136, 142, 151, 317space travel, 141, 141specific heat capacity, 256–258speed

average, 109fluid pressure and, 173kinetic energy and, 215of light, 566–567, 577of sound, 539–540velocity and, 110wave, 519, 519, 521, 521wing shape and, 175

Spencer, Percy, 591spider silk, 386, 395, 395spider webs, 386, 386spoilers, 176Sprague, Frank J., 450Sputnik I, 2, 2stainless steel, 417standing wave, 524, 524,

549–550. See also wavesstarches, 384states of matter, 58–73, 260.

See also matterchange of state, 68–73, 261defined, 44, 60, 60, 260

static cling, 335, 335static electricity, 427, 427–429,

446static friction, 122, 122Statue of Liberty, 50, 292, 292steam engines, 60, 60, 79, 266,

266steam-heating systems, 263steel, 47, 171, 171stimulated emission, 610straight chain structures, 383streetcars, 450, 450string instruments, 553, 553strong force, 293, 402strontium, 322stylus, 490, 490sublimation, 68, 68, 72submarines, 172subscripts, 352, 352, 743substances, pure, 82sucrose, 339sugar, 48, 219, 339, 339, 352,

362, 384, 384sulfur, 80, 307, 315, 322, 331sulfur dioxide, 51

sulfuric acid, 51, 378sun

energy from, 221, 221, 235,237, 432

gravity and, 128, 128nuclear fusion in, 221solar heating systems, 265,

265volume of, 36

sunscreens, 573superconductors, 274, 418, 436,

436superglue, 326surface area, 365surfaces, 119, 119–120, 124surface tension, 63, 63surface waves, 515, 515suspensions, 96, 99swim bladders, 172, 172switches, 441, 441symbols, 27, 27, 308, 354–355synthesis reactions, 358, 358.

See also chemical reactions

TTacoma Narrows Bridge, collapse

of, 525, 525technology, 11–12telecommunication, 488.

See also communication technology

telegraphs, 488, 488telephones, 419, 419, 489, 489telescopes, 609, 609

radio, 530, 530television, 480, 480, 493, 493,

570, 584Telkes, Maria, 184, 184tellurium, 307temperature

change of state and, 68, 73conversions, 249defined, 246of gases, 65–66infrared waves and, 571kinetic energy and, 247, 247measurement, 248–249nuclear fusion and, 410overview, 246–247


Index 789

IND

EX

reaction rates and, 364resistance and, 436scales, 248, 249solubility and, 95, 95speed of sound and, 540thermal energy and, 259thermal equilibrium, 252,

252units, 24, 26, 248, 248–249,

730volume and, 250

tension, 135terminal velocity, 140theories, scientific, 19, 23, 280,

328thermal conductivity, 44, 306–307thermal energy. See also heat;

temperaturecalculations, 257from chemical reactions, 361conversions, 223, 225, 227,

229, 231defined, 218heat and, 252–253, 259heat engines, 266kinetic energy and, 218, 218matter and, 260particles and, 218, 218from solar cells, 235, 235

thermal equilibrium, 252, 252thermal expansion, 248, 250,

250thermal pollution, 269thermocouples, 432, 432thermometers, 26, 248,

248–249thermostats, 250, 250third class lever, 199, 199.

See also leversThomson, J. J., 277, 282–283threads, of screw, 202Three Mile Island, 324thrust, 175, 182thunderstorms, 428, 428–429,

446thyroid, 405tin, 48, 314tinnitus, 538tire pressure, 67, 162Titanic, 80, 80, 165titanium, 309, 312, 312

as bone replacement, 57, 312, 312

total internal reflection, 612tracers, 405traffic lights, 618transformers, 472, 472, 473transistors, 418, 418, 485,

485–487, 486, 487transition metals, 312–313translucent materials, 582,

582–583transmission of light, 581,

581–582transmutation, 400transparent materials, 582,

582–583transverse waves, 513, 513,

515, 516–517Travers, Morris W., 277Triantafyllou, Michael, 4, 12,

12–17Trieste, 165triple-beam balance, 731trolley, 450, 450troughs, 513, 513tsunamis, 508tungsten filaments, 435, 595tuning fork, 507turbine

steam, 234water, 235wind, 228, 228, 236

turbulence, 176Tyrannosaurus rex, 278

Uultrasonic frequencies, 541, 546ultrasonography, 547, 547ultraviolet (UV) light, 346, 569,

573unbalanced forces, 117–118United Nations, 276universal gravitation, law of,

105, 126–128, 127universal solvent, water as, 92unsaturated hydrocarbons, 388,

388ununnilium, 308uranium, 235, 402, 404, 406,

406–407Uranus, 105, 105urea, 324

urine, 324useful equations, 748

Vvacuum tubes, 487, 487valence electrons, 329,

329–331, 330, 331. See also electrons

vaporization, 68, 70, 70–72variables, 15velocity, 110–112, 111

of falling objects, 139terminal, 140

Venus, 105, 128vibrations, 220, 511, 511

sound and, 534, 534–535, 553, 554

vinegar, 348, 348as an acid, 378, 378

viper fish, 165virtual images, 599, 599,

600–601, 601, 602, 603, 604

virtual reality devices, 134viscosity, 63visible light, 572, 572vision problems, 606, 606–607,

607. See also sightvitamin D, 573vocal chords, 535voltage, 431, 431, 434–435,

437, 447, 472, 473volts, 434–435, 437volume

calculation of, 25, 38, 45defined, 741gases and, 38, 63, 63, 65–66measurement of, 36–38units, 24, 25, 25, 729

Wwarm-air heating, 264waste thermal energy, 231water

alkali metals in, 311, 311boiling point of, 248change of state, 68, 68–72,


Index790

IND

EX

261, 261composition of, 86, 352as conductor, 375–376, 427decomposition reaction, 359density of, 45energy from, 235, 237freezing point of, 248heating systems, 263, 263molecules, 337, 338pH of, 380pressure, 162, 165, 165specific heat capacity,

256–258as a universal solvent, 92

Watt, James, 79watts, 191, 437–439wavelength, 517, 517–518, 518,

564–574, 579waves, 508–525. See also

light; soundabsorption and scattering,

576, 576–577amplitude, 516, 516–517,

542–544, 544calculations, 519compressions, 514, 514crests, 513, 513defined, 510diffraction, 521–522, 522,

551, 551, 579, 579electromagnetic, 492, 492,

512–513, 564, 564–565, 567–574

energy in, 510–512frequency of, 518, 540,

540–541, 541, 544infrared, 482, 568, 571, 571interactions, 520–525interference and, 522–524,

548, 548–550, 579–580, 580

longitudinal, 514, 514–515, 515, 517, 535, 535

mechanical, 511medium and, 511microwaves, 568, 570–571properties of, 516–519radio, 492, 492, 536,

567–570, 568, 569rarefactions, 514, 514reflection, 520, 520, 545,

545–547, 575, 575–576, 576

refraction, 521, 521, 577,577–578, 578

resonance, 524–525seismic, 511sound, 515, 515standing, 524, 524, 549–550surface, 515transverse, 513, 513, 515,

516–517, 564, 564troughs, 513, 513units, 518wavelength, 517, 517–518,

518, 572, 579wave speed, 519, 519, 521,

521weak force, 293weather, 71

models and, 21, 21weather balloons, 66Webb, Gene, 10wedges, 201, 201weight

buoyant force and, 169, 169in free fall, 141, 141gravity and, 128–129, 129,

216, 216–217mass and, 39–41, 41, 129

wet cells, 431wheel and axle, 202, 202–203,

203Wichterle, Otto, 347Williams-Byrd, Julie, 32, 32Williamson, Tom, 560WIMPs (Weakly Interacting

Massive Particles), 56wind energy, 228, 236, 237wind instruments, 554, 555wing shape, 174, 174–176, 175wiring, 436, 436, 440, 447work

calculation of, 190, 190, 749defined, 188, 749energy and, 214, 214–217input/output, 193, 193–194,

195, 197machines and, 192–194overview, 188–189, 189power and, 191units, 190

World’s Fair, 3Wright, Orville, 174

Xxenon, 277, 317X rays, 569, 569, 574, 574

YYeager, Chuck, 104, 540Yeager, Jeana, 326Young, Thomas, 507Yucca Mountain, 416

Zzinc, 45, 377zinc chloride, 359zipper, 185, 185, 205, 205



Credits 791

CR

ED

ITS

CreditsAbbreviations used: (t) top, (c) center, (b) bottom, (l) left, (r) right, (bkgd) back-ground

ILLUSTRATIONSAll illustrations, unless noted below, by Holt, Rinehart and Winston.

Table of Contents Page v(bl), Kristy Sprott; vii(tl), ix(tr), Stephen Durke/WashingtonArtists; ix(bl), Keith Locke/Suzanne Craig; xi(tr), Stephen Durke/Washington Artists;xi(tl), Terry Kovalcik; xii(tl), Stephen Durke/Washington Artists; xii(bl), BlakeThornton/Rita Marie; xiii(bl), Stephen Durke/Washington Artists; xiv(tl), BlakeThornton/Rita Marie; xv(cr), Sidney Jablonski; xv(bl), Marty Roper/Planet Rep; xvi(t),Annie Bissett.

Chapter One Page 6, 9, Rainey Kirk/The Neis Group; 13, John Huxtable/Black, Inc.; 14, Will Nelson/Sweet Reps; 16, Preface, Inc.; 17, Terry Guyer; 18(b), Brian White; 20(tr),Kristy Sprott; 20(bl) Morgan Cain & Associates; 21(t), Stephen Durke/WashingtonArtists; 21(c), Keith Locke/Suzanne Craig; 21(b) Gary Antonetti/Ortelius Design; 22(cl),Kristy Sprott; 22(b), Blake Thornton/Rita Marie; 23(t), Stephen Durke/WashingtonArtists and Preface, Inc.; 24(all), Stephen Durke/Washington Artists; 26(t), Morgan Cain& Associates; 29, Blake Thornton/Rita Marie; 31(tl), David Merrell/Suzanne Craig.

Chapter Two Page 38(t), 39, Stephen Durke/Washington Artists; 42(l), GaryLocke/Suzanne Craig; 43, Blake Thornton/Rita Marie; 50, 51, 53, Marty Roper/Planet Rep; 55(lc), Terry Kovalcik; 57(tc), Daniels & Daniels.

Chapter Three Page 60(t), Mark Heine; 60(b), 61, 62, 63, 64, 65, 66(cl,cr), Stephen Durke/Washington Artists; 66(bl), Preface, Inc.; 68, David Schleinkofer/Mendola Ltd.; 70(t), Marty Roper/Planet Rep; 70(b), Mark Heine; 73, DavidSchleinkofer/Mendola Ltd. and Preface, Inc.; 74(t), Stephen Durke/WashingtonArtists; 74(b), Preface, Inc.; 75, Marty Roper/Planet Rep; 77(cr), Preface, Inc.

Chapter Four Page 82, Marty Roper/Planet Rep; 84(b), Preface, Inc.; 88, BlakeThornton/Rita Marie; 95, Preface, Inc.

Chapter Five Page 109, Preface, Inc.; 111, Marty Roper/Planet Rep; 112, GaryLocke/Suzanne Craig; 113(t), Mike Carroll/Steve Edsey & Sons; 114(cr), Preface, Inc.;119(t), Blake Thornton/Rita Marie; 119(b), 120, 122, Gary Ferster; 126, Doug Henry/American Artists; 127, Stephen Durke/Washington Artists; 128, Craig Attebery/Frank & Jeff Lavaty; 129, Terry Guyer; 130(br), Stephen Durke/Washington Artists;131, Terry Guyer; 133(r), Preface, Inc.

Chapter Six Page 139, 140, Gary Ferster; 142, Craig Attebery/Frank & Jeff Lavaty;144(tl), Mike Carroll/Steve Edsey & Sons; 146, Marty Roper/Planet Rep; 148, CharlesThomas; 151(tr), Gary Ferster; 154(br), Craig Attebery/Frank & Jeff Lavaty; 155, MartyRoper/Planet Rep; 158, James Pfeffer.

Chapter Seven Page 160, Rainey Kirk/The Neis Group; 162, 163, Stephen Durke/Washington Artists; 164, 165, Rainey Kirk/The Neis Group; 166, Christy Krames; 167,Mark Heine; 168, Preface, Inc.; 169, Will Nelson/Sweet Reps; 171, Preface, Inc.; 172,Sam Collins/Art & Science, Inc.; 174(c), Craig Attebery/Frank & Jeff Lavaty; 174(bl),Will Nelson/Sweet Reps; 176(l), Marty Roper/Planet Rep; 177, Terry Guyer; 178, CraigAttebery/Frank & Jeff Lavaty; 181(tr), Jared Schneidman/ Wilkinson Studios; 181(bl),Keith Locke/Suzanne Craig.

Chapter Eight Page 189(tr), Blake Thornton/Rita Marie; 190, John White/The NeisGroup; 195(l), Annie Bissett; 195(r), John White/The Neis Group; 196, Keith Locke/Suzanne Craig; 198(l), 199(tl, bl), Annie Bissett; 201(cl), Preface, Inc.; 203(t), GaryFerster; 203(c,b), 204, John White/The Neis Group; 206, Blake Thornton/Rita Marie.

Chapter Nine Page 215(b), Dave Joly; 216, John White/The Neis Group; 218, StephenDurke/Washington Artists; 219(t), Kristy Sprott; 219(b), Stephen Durke/WashingtonArtists; 220(t), Gary Ferster; 224, Will Nelson/Sweet Reps; 225, Dan Stuckenschneider/Uhl Studios Inc.; 226(t), Blake Thornton/Rita Marie; 227, Dan Stuckenschneider/UhlStudios Inc.; 229, Dan McGeehan/Koralik Associates; 230(t), Marty Roper/Planet Rep;230(b), 232(b), Dan Stuckenschneider/Uhl Studios Inc.; 233(r), Preface, Inc.; 234,Patrick Gnan/Deborah Wolfe; 235(br), Michael Moore; 236(cr), Dan Stuckenschneider/Uhl Studios Inc.; 237(b), Preface, Inc.; 241(r), Dave Joly.

Chapter Ten Page 246, Blake Thornton/Rita Marie; 247, Stephen Durke/WashingtonArtists; 248, Terry Guyer; 249(tr), Dave Joly; 250, Dan Stuckenschneider/Uhl StudiosInc.; 252, 253, Stephen Durke/Washington Artists; 254(bl), Mark Heine; 255, JaredSchneidman/Wilkinson Studios; 258, 260, Stephen Durke/Washington Artists; 261,Preface, Inc.; 263, 264, 265, 266, 268, 269, Dan Stuckenschneider/Uhl Studios Inc.;270(c), Dave Joly; 272(br), Dan Stuckenschneider/Uhl Studios Inc.; 273(cr), Preface,Inc.; 275, Stephen Durke/Washington Artists.

Unit Four Page 276(cr), Stephen Durke/Washington Artists.

Chapter Eleven Page 281(c), Preface, Inc.; 282, Mark Heine; 283, Stephen Durke/Washington Artists; 284(c), Mark Heine; 284(b), Preface, Inc.; 285(t), StephenDurke/Washington Artists; 285(br), Preface, Inc.; 286, 288, 289(t,b), Stephen Durke/Washington Artists; 289(cr), Terry Kovalcik; 290, 291(b), 293, 294(br), StephenDurke/Washington Artists; 295, Terry Kovalcik; 296, Mark Heine; 297(r), StephenDurke/Washington Artists.

Chapter Twelve Page 302, Michael Jaroszko/American Artists; 304, 305, KristySprott; 306(tr), 307, Stephen Durke/Washington Artists; 309, 310(bc), 311(bl),312(t), 313(t), 314(tc, b), Preface, Inc.; 314(l), Gary Locke/Suzanne Craig; 315, 316,317(lc), Preface, Inc.; 319, Gary Locke/Suzanne Craig; 321(tr), Preface, Inc.; 321(bl),Keith Locke/Suzanne Craig; 321(br), Annie Bissett; 323(l), Dan Stuckenschneider/Uhl Studios Inc.

Unit Five Page 324(cr), Kristy Sprott.

Chapter Thirteen Page 329, Stephen Durke/Washington Artists; 330, Preface, Inc.;331, 333, 334, Stephen Durke/Washington Artists; 335(t), Keith Locke/SuzanneCraig; 335(br), Kristy Sprott; 336(c), 337(tl), Stephen Durke/Washington Artists;337(tr,c), Preface, Inc.; 338(tr,br), Kristy Sprott; 338(bl), Stephen Durke/Washington

Artists; 339, Kristy Sprott; 340(cl), 341(tc), Kristy Sprott; 341(br), Preface, Inc.; 342(t),Keith Locke/Suzanne Craig; 342(b), Stephen Durke/Washington Artists; 343, KristySprott; 344(b), Stephen Durke/Washington Artists; 346, Kristy Sprott.

Chapter Fourteen Page 352(t), 356, Kristy Sprott; 358(b), 359(c,b), 360(b), BlakeThornton/Rita Marie; 363(t), 365(b), Preface, Inc.; 366, Blake Thornton/Rita Marie;367, Kristy Sprott; 369(cr), Preface, Inc.

Chapter Fifteen Page 380(t), Dave Joly; 380(b), 383, Preface, Inc.; 384, 385(b),Morgan Cain & Associates; 388, 389(t), 393(tr), Preface, Inc.

Chapter Sixteen Page 399, 400, Stephen Durke/Washington Artists; 401, GaryFerster; 402, 403, Stephen Durke/Washington Artists; 404, Preface, Inc.; 406, 407,Stephen Durke/Washington Artists; 408, Patrick Gnan/Deborah Wolfe Ltd.; 410(c),412(br), 414, Stephen Durke/Washington Artists; 415(tr), Preface, Inc.

Chapter Seventeen Page 422(t), Blake Thornton/Rita Marie; 422(b), StephenDurke/Washington Artists; 423, John White/The Neis Group; 425(l), Stephen Durke/Washington Artists; 428, Dan Stuckenschneider/Uhl Studios Inc.; 430, 432, MarkHeine; 433, 434, Geoff Smith/Scott Hull; 436, Will Nelson/Sweet Reps; 439(cr),Boston Graphics; 444, Dan McGeehan/Koralik Associates.

Chapter Eighteen Page 456, 457, 458, Stephen Durke/Washington Artists; 459,Mark Persyn; 460(b), Stephen Durke/Washington Artists; 462, 463, 465, SidneyJablonski; 466, Patrick Gnan/Deborah Wolfe Ltd.; 467, Stephen Durke/WashingtonArtists; 468, Mark Heine; 469, 470(t), Mark Persyn; 470(b), 471(t), David Fischer;471(b), John Francis, 472, Tony Randazzo; 473, Dan Stuckenschneider/Uhl Studios Inc.; 474(l), Sidney Jablonski; 474(r), Mark Persyn; 475, David Fischer; 477, Stephen Durke/Washington Artists.

Chapter Nineteen Page 483, 484(c), Stephen Durke/Washington Artists; 484(b),Gary Ferster; 485, Blake Thornton/Rita Marie; 486, Gary Ferster; 489, 490(tl), DanStuckenschneider/Uhl Studios Inc.; 490(b), 491(tr), Gary Ferster; 491(b), StephenDurke/Washington Artists; 492, Blake Thornton/Rita Marie; 493, Dan Stuckenschneider/Uhl Studios Inc.; 494, Preface, Inc.; 499, Blake Thornton/Rita Marie; 500(bl), StephenDurke/Washington Artists; 500(br), Blake Thornton/Rita Marie; 502(cl), 503(tr), Gary Ferster.

Chapter Twenty Page 508(t), Gary Antonetti/Ortelius Design; 510, Will Nelson/Sweet Reps; 513(tr), Preface, Inc.; 513(b), 514(t,c), John White/The Neis Group;514(b), Sidney Jablonski; 515(tl), Stephen Durke/Washington Artists; 515(r), Jared Schneidman/Wilkinson Studios; 516(t), Marty Roper/Planet Rep; 516(b), 517,518, Sidney Jablonski; 518(cl, cr), 519(cl,cr), Mike Carroll/Steve Edsey & Sons; 519,521, Will Nelson/Sweet Reps; 523(tl,tc,tr,cl,c,cr), John White/The Neis Group; 523(br),Terry Guyer; 526(b), John White/The Neis Group; 529(r), Sidney Jablonski.

Chapter Twenty-one Page 534, Annie Bissett; 535(l), Gary Ferster; 535(br), TerryKovalcik; 536(tl), David Merrell/Suzanne Craig; 537, Keith Kasnot; 538 (tl), TerryKovalcik; 539, Keith Locke/Suzanne Craig; 540, Annie Bissett; 541, Will Nelson/SweetReps (dolphin, cat, dog), Rob Wood (whale), Michael Woods (bat, bird), John White/The Neis Group (girl), and Preface, Inc.; 542, Gary Ferster; 544, Annie Bissett; 545(b),John White/The Neis Group; 546(t), Gary Ferster; 546(b), Terry Guyer; 548(t), GaryFerster; 548(b), 549, Terry Guyer; 551, 552(c), Gary Ferster; 552(b), 555, AnnieBissett; 556(br), Keith Kasnot; 559(r), Annie Bissett; 560, Barbara Hoopes-Ambler.

Chapter Twenty-two Page 564, Sidney Jablonski; 565(tr), Blake Thornton/RitaMarie; 565(b), Stephen Durke/Washington Artists; 568(t), Blake Thornton/Rita Marie;568(b), Preface, Inc.; 569(tl,tr), Terry Guyer; 569 (b), Preface, Inc.; 570, DanStuckenschneider/Uhl Studios Inc.; 572, Preface, Inc.; 573, Blake Thornton/RitaMarie; 574, 575, 576, Dan Stuckenschneider/Uhl Studios Inc.; 578, Stephen Durke/Washington Artists; 580, Preface, Inc.; 582, Dave Joly; 583, Preface, Inc.; 586,Stephen Durke/Washington Artists.

Chapter Twenty-three Page 595, 596, 597, Dan Stuckenschneider/Uhl Studios Inc.;598, Stephen Durke/Washington Artists; 599, Preface, Inc.; 601, 602, 603, 604, WillNelson/Sweet Reps (flowers) and Preface, Inc.; 605, Keith Kasnot; 606, Keith Kasnotand Preface Inc.; 608, 609, Dan Stuckenschneider/Uhl Studios Inc.; 610(t), DigitalArt; 610(b), Stephen Durke/Washington Artists; 611, Digital Art; 612, Stephen Durke/Washington Artists; 614(t), Dan Stuckenschneider/Uhl Studios Inc.; 614(b), KeithKasnot; 617, Stephen Durke/Washington Artists (rulers) and Preface, Inc.

LabBook Page 642, Blake Thornton/Rita Marie; 661, Preface, Inc.; 665(l), JohnWhite/The Neis Group; 669, Dan McGeehan/Koralik Associates; 671, Marty Roper/Planet Rep.; 674, Dave Joly; 677(t), Preface, Inc.; 680, Stephen Durke/WashingtonArtists; 689, Preface, Inc.; 695(tr), Gary Ferster; 695(br), Dave Joly; 712, BlakeThornton/Rita Marie; 716, Terry Guyer; 718, Stephen Durke/Washington Artists; 721,722, John White/The Neis Group.

Appendix Page 727, Blake Thornton/Rita Marie; 730(t), Terry Guyer; 734(b), MarkMille/Sharon Langley Artist Rep.; 735, 736, 737, Preface, Inc.; 742, Stephen Durke/Washington Artists; 743(tl,c), Kristy Sprott; 743(b), Bruce Burdick; 744, 745, KristySprott; 747(t), Dan Stuckenschneider/Uhl Studios Inc.

PHOTOGRAPHYFront Cover (tl) Ed Young/Science Photo Library/Photo Researchers, Inc.; (tr) FPGInternational; (bl) Henry Kaiser/Leo de Wys; (br) Firefly Productions/The StockMarket (also on title page); (cr) Stephen Dalton/Photo Researchers, Inc.; owl (frontcover, back cover, spine and title page) Kim Taylor/Bruce Coleman, Inc.

Table of Contents Page v(tr), Robert Daemmrich/Tony Stone Images; (br), PeterVan Steen/HRW Photo; vi(cl), Richard Megna/Fundamental Photographs; (bl), JosephDrivas/Image Bank; vii(bl), Richard Megna/Fundamental Photographs; viii(tr), JamesBalog/Tony Stone Images; (cl), Sergio Purtell/FOCA; (bl) NASA; ix(tl), T. Mein/N&MMischler/Tony Stone Images; x(tr), NASA; xiii(br), Dr. E.R. Degginger/Color-Pic, Inc.;xiv(t), Stephanie Morris/HRW Photo; xv(inset), Archive Photos; xvi(bl), LeonardLessin/Peter Arnold, Inc.; xvii(tr), Harry Rogers/Photo Researchers, Inc.; (tl), RobertWolf; xxi(br), Superstock.

Feature Borders Unless otherwise noted below, all images ©2001 PhotoDisc/HRW: “Across the Sciences” Pages 56, 135, 242, 267, 322, 370, 418, 448, all imagesby HRW; “Careers” 32, 159, 243, 323, 395, 509, sand bkgd and saturn, CorbisImages, DNA, Morgan Cain & Associates, scuba gear, ©1997 Radlund & Associates for Artville; “Eureka” 79, 158, 182, 211, 371, ©2001 PhotoDisc/HRW; “Eye on the


Credits792

CR

ED

ITS

Credits

Environment” 394, clouds and sea in bkgd, HRW, bkgd grass and red eyed frog,Corbis Images, hawks and pelican, Animals Animals/Earth Scenes, rat, John Grelach/Visuals Unlimited, endangered flower, Dan Suzio/Photo Researchers, Inc.; “HealthWatch” 57, dumbell, Sam Dudgeon/HRW Photo, aloe vera and EKG, Victoria Smith/HRW Photo, basketball, ©1997 Radlund & Associates for Artville, shoes and Bubbles,Greg Geisler; “Scientific Debate” 449, 480, Sam Dudgeon/HRW Photo; “ScienceFiction” 33, 103, 183, 481, saucers, Ian Christopher/Greg Geisler, book, HRW, bkgd,Stock Illustration Source; “Science, Technology, and Society” 78, 102, 134, 210, 266,298, 346, robot, Greg Geisler; “Weird Science” 299, 347, 419, 508, mite, DavidBurder/Tony Stone, atom balls, J/B Woolsey Associates, walking stick and turtle,EclectiCollection.

Unit One Page 2(t), Corbis-Bettman; 2(cl), Photosource; 2(b), Enrico Tedeschi; 3(tl), Sam Shere/Corbis Bettmann; 3(tr), Brown Brothers/HRW Photo Library; 3(bl), Natalie Fobes/Tony Stone Images; 3(br), Noble Proctor/Science Source/PhotoResearchers, Inc.

Chapter One Page 4(t), David Lawrence/The Stock Market; 4(b), Donna Coveney/MIT News; 7(t), Jeff Hunter/The Image Bank; 7(b), Scala/Art Resource, NY; 8(b),Gunnar Kullengerg/Stock Connection/PNI; 9(tr), Chris Madley/Science Photo Library/Photo Researchers, Inc.; 9(bkgd), Joseph Nettis/Photo Researchers, Inc.; 9(cl), StuartWestmorland/Photo Researchers, Inc.; 9(br), M.H. Sharp/Photo Researchers, Inc.;9(cr), David R. Frazier Photolibrary; 9(b), Norbert Wu; 10 (tl), John Langford/HRWPhoto; 10(tr), courtesy of the U.S. Nuclear Regulatory Commission; 10(cr), MicheleForman; 12(br), HRW photo by Stephen Maclone; 12(bl), Barry Chin/Boston Globe;15, Donna Coveney/MIT News; 19(t), Chris Butler/Science Photo Library/PhotoResearchers, Inc.; 19(b), Richard Megna/Fundamental Photographs; 20(br),Rosenfeld Images LTD/Science Photo Library/Photo Researchers, Inc.; 23(b), courtesyof FHWA/NHTSA National Crash Analysis/The George Washington University; 25(bl,r),HRW photo by Peter Van Steen; 27, Image ©2001 PhotoDisc, Inc.; 28(c), TomMcHugh/Steinhart Aquarium/Photo Researchers, Inc.; 31(cr), HRW photo by VictoriaSmith; 32(all), HRW photos by Art Louis.

Chapter Two Page 34(l), Hartmann/Sachs/Phototake, NY; 34(c), Ken Lucas/VisualsUnlimited; 34(r), The Granger Collection, NY; 34(tr), Image ©2001 PhotoDisc, Inc.;36(b), NASA, Media Services Corp.; 40(all), John Morrison/Morrison Photography;41(t), HRW photo by Michelle Bridwell; 43-44(all), John Morrison/MorrisonPhotography; 45, Neal Nishler/Tony Stone Images; 46(all), John Morrison/MorrisonPhotography; 47, Rob Boudreau/Tony Stone Images; 48(t), Brett H. Froomer/TheImage Bank; 48(cl,cr), John Morrison/Morrison Photography; 49, HRW photo byLance Schriner; 50(tl,tr), John Morrison/Morrison Photography; 50(bl), JosephDrivas/The Image Bank; 50(br), SuperStock; 52(r), HRW photo by Michelle Bridwell;55, HRW photo by Lance Schriner; 56, David Malin/©Anglo-Austrailian Observatory/Royal Observatory, Edinburgh.

Chapter Three Page 58(r), Tony Stone Images; 58(l), Peter Menzel; 61(t), Gilbert J.Charbonneau; 63(t), Dr. Harold E. Edgerton/©The Harold E. Edgerton 1992 Trust/courtesy Palm Press, Inc.; 67(b), Pekka Parviainen/Science Photo Library/PhotoResearchers, Inc.; 68, Union Pacific Museum Collection; 69(t), Richard Megna/Fundamental Photographs; 76(t), Myrleen Ferguson/PhotoEdit; 77, Charles D.Winters/Photo Researchers, Inc.; 78(l), Kennan Ward Photography; 78(r), Dr. Jean-Claude Diels/University of New Mexico; 79, Union Pacific Museum Collection.

Chapter Four Page 80(l), Fr. Browne S.J. Collection; 80(r), RMS Titanic Inc.; 82(r),David R. Frazier Photolibrary; 82(l), Jonathan Blair/Woodfin Camp & Associates;83(b), Russ Lappa/Photo Researchers, Inc.; 83(t,c), Charles D. Winters/PhotoResearchers, Inc.; 84(t,l), Walter Chandoha; 84(r), Zack Burris; 84(b), Yann Arthus-Bertrand/Corbis; 85(tc), HRW photo by Victoria Smith; 85(cl), Dr. E.R. Degginger/Color-Pic, Inc.; 85(cr), Runk/Schoenberg/Grant Heilman Photography Inc.; 85(br),Joyce Photographics/Photo Researchers, Inc.; 85(l), Russ Lappa/Photo Researchers,Inc.; 85(bc), Charles D. Winters/Photo Researchers, Inc.; 86(c), Runk/Schoenberger/Grant Heilman; 87(l), Runk/Shoenberger/Grant Heilman Photography; 87(b), Richard Megna/Fundamental Photographs; 88, Runk/Schoenberg/Grant HeilmanPhotography Inc.; 88, Richard Megna/Fundamental Photographs; 89(t), JohnKapriellan/Photo Researchers, Inc.; 90(l), HRW photo by Victoria Smith; 91(t),Charles D. Winters/Timeframe Photography; 91(c), Charles Winters/PhotoResearchers, Inc.; 91(cr), Klaus Guldbrandsen/Science Photo Library/PhotoResearchers, Inc.; 93(b), HRW photo by Richard Haynes; 93(c), Image ©2001PhotoDisc, Inc.; 94(c), Dr. E.R. Degginger/Color-Pic, Inc.; 96(c), HRW photo byMichelle Bridwell; 97(t), HRW photo by Lance Schriner; 97(b), Dr. E.R. Degginger/Color-Pic, Inc.; 98(b), HRW photo by Victoria Smith; 98(t), David R. FrazierPhotolibrary; 100(t), Yann Arthus-Bertrand/Corbis; 101(t), Richard Megna/Fundamental Photographs; 102(l), Anthony Bannister/Photo Researchers, Inc.;102(r), Richard Steedman/The Stock Market.

Unit Two Page 104(tl), Archive Photos; 104(tr), Image ©1998 PhotoDisc, Inc.;104(bl), Photo Researchers, Inc.; 104(br), Underwood & Underwood/Corbis-Bettman;105(tl), The Vittoria, colored line engraving, 16th century/The Granger Collection, NY;105(tr), Stock Montage, Inc.; 105(cl), NASA/Science Source/Photo Researchers, Inc.;105(cr), W.A. Mozart at the age of 7: oil on canvas, 1763, by P.A. Lorenzoni/TheGranger Collection, NY; 105(b), NASA.

Chapter Five Page 106(c), George Catlin, Ball of Play of the Choctaw/NationalMuseum of American Art, Washington D.C./Art Resource, NY; 106(b), LawrenceMigdale; 108(all), SuperStock; 110(t), Tom Tietz/Tony Stone Images; 110(b), RobertGinn/PhotoEdit; 113, Sergio Putrell/Foca; 114(t), Gene Peach/The Picture Cube; 115,116(b), HRW photos by Michelle Bridwell; 117, HRW photo by Daniel Schaefer;118(t), David Young-Wolff/PhotoEdit; 118(b), Arthur C. Smith/Grant HeilmanPhotography; 121(all), HRW photos by Michelle Bridwell; 121(insets), HRW photosby Stephanie Morris; 122, Tony Freedman/PhotoEdit; 124(cl), HRW photo byMichelle Bridwell; 125, NASA; 128, Image ©2001 PhotoDisc; 130(c), Superstock; 133, HRW photo by Mavournea Hay; 134, Hunter Hoffman; 135, Bruce Hands/Tony Stone Images.

Chapter Six Page 136(b), David R. Frazier Photography; 136(all), 137(t), NASA; 138,Richard Megna/Fundamental Photographs; 139, Doug Armand/Tony Stone Images;140, Robert Daemmrich/Tony Stone Photography; 141(t), James Sugar/Black Star;141(b), NASA; 143(b), James Balog/Tony Stone Images; 143(l), Michelle Bridwell/Frontera Fotos; 143(r), Image ©2001 PhotoDisc, Inc.; 144(t), Richard Megna/Fundamental Photographs; 146, Marc Asnin/SABA Press Photos, Inc.; 147(l), HRWphoto by Mavournea Hay; 147(r), Michelle Bridwell/Frontera Fotos; 149(all), Image

©2001 PhotoDisc, Inc.; 150, David Madison; 151(tl), Gerard Lacz/Animals Animals/Earth Sciences; 151(tc), HRW photo by Coronado Rodney Jones; 151(tr), Image©2001 PhotoDisc, Inc.; 151(bl), NASA; 151(br), HRW photo by Lance Schriner;152(all), HRW photos by Michelle Bridwell; 153(t), Zigy Kaluzny/Tony Stone Images;153(b), HRW Photo by Michelle Bridwell; 154, Robert Daemmrich/Tony StonePhotography; 156(t), James Balog/Tony Stone Images; 156(b), David Madison/TonyStone Images; 157(l), NASA; 158(t), courtesy of Steve Okamoto; 158(b), Lee Schwabe;159, R.N. Metheny/The Christian Science Monitor.

Chapter Seven Page 159(t), courtesy of Steve Okamoto; 159(b), Lee Schwabe;164(t), I. M. House/Tony Stone Images; 164(tc), David R. Frazier Photolibrary, Inc.;164(c), Deiter and Mary Plage/Bruce Coleman; 164(bc), Wolfgang Kaeler/Corbis;164(b), Martin Barraud/Tony Stone Images; 165(t), SuperStock; 165(tc), Daniel A.Nord; 165(c), Ken Marschall/Madison Press Books; 165(bc), Bassot/PhotoResearchers Inc.; 165(b), Bettmann Archive; 168, HRW photo by Michelle Bridwell;170, Bruno P. Zehnder/Peter Arnold, Inc.; 173, Richard Megna/FundamentalPhotographs; 175(t), Larry L. Miller/Photo Researchers, Inc.; 175(c), Richard Neville/Check Six; 175(bl), T. Mein/N&M Mishler/Tony Stone Images; 175(t), Larry L. Miller/Photo Researchers, Inc.; 176 (t), Ron Kimball/Ron Kimball Photography, Inc.; 176(t),HRW Photo by Michelle Bridwell; 177(b), George Hall/Check Six; 179(t), Ron Kimball/Ron Kimball Photography, Inc.; 182 (t), Victor Malafronte.

Unit Three Page 184(t); The Granger Collection, New York; 184(b); ConleyPhotography, Inc./American Solar Energy Society; 184(c); The Granger Collection, NY;185(tl); Phil Degginger/Color-Pic, Inc.; 185(tr); Corbis-Bettmann; 185(cr); RobertWolf; 185(cl); The Granger Collection, NY; 185(b); David Madison.

Chapter Eight Page 186(b), Yoram Lehman/Peter Arnold Inc., NY; 186, 187(t), Erich Lessing/Art Resource/NY ; 192(cl,cr,bc,br,t) Robert Wolf; 192(bl), image copy-right 2001 PhotoDisc, Inc.; 197, 198(l,r), 199 (c), Robert Wolf; 200, Lisa Davis;201(b,c), 202(t,b), Robert Wolf; 204(t), HRW photo by Russell Dian; 204(b), RobertWolf; 205(tl), Image copyright1998 PhotoDisc, Inc.; 205(tc), 208(t), Robert Wolf;209(l), Helmut Gritscher/Peter Arnold, Inc.; 209(br), HRW photo by Stephanie Morris;210, courtesy of IBM Corp., Research Division, Almaden Research; 211, A.W.Stegmeyer/Upstream.

Chapter Nine Page 212, courtesy of L. Stern and J. Pinkston, US Geological Survey;214, Al Bello/Allsport; 216, Earl Kowall/Corbis; 218(c), Paul A. Souders/Corbis;218(r), Tony Freeman/Photo Edit; 221(t), NASA; 221(b), Mark C. Burnett/PhotoResearchers, Inc.; 222(l,cl,cr,r), HRW photo by Peter Van Steen; 223(t), RichardMegna/Fundamental Photographs; 228, Morton Beebe/Corbis; 231, HRW photobyVictoria Smith; 232, Ted Clutter/Photo Researchers, Inc.; 233(t), Tom Carroll/Phototake; 233(cl), Mark E. Gibson ; 233(br), John Kaprielian/Photo Researchers,Inc.; 234(t), Robert Wolf; 235(t), D.O.E./Science Source/Photo Researchers, Inc.;235(cl), H.P. Merton/The Stock Market; 235(b), Tom Carroll/Phototake; 235(bl), HRW photo by Coronado Rodney Jones; 235 (br), Kevin R. Morris/Corbis; 236(tl),Bob Gomel/The Stock Market; 236(tr), Ed Young/Corbis; 236(c), Richard Nowitz/Phototake; 239, Ed Young/Corbis; 240(b), Ted Clutter/Photo Researchers, Inc.;241(bl), Mike Powell/Allsport; 242, Solar Survival Architecture; 243(t,b), Robert Wolf.

Chapter Ten Page 244(t), Solar Survival Architecture; 250, Mark Burnett/PhotoResearchers, Inc.; 259, L.D. Gordon/The Image Bank; 262, HRW Photo by Peter VanSteen; 267(t), Dorling Kindersley LTD; 267(b), Peter Arnold Inc., NY; 272, DorlingKindersley LTD; 273, Kees van den Berg/Photo Researchers, Inc.; 274, Dan Winters/Discover Magazine.

Unit Four Page 276(t), The Granger Collection, New York; 277(t), SuperStock;277(b), Reuters/Mark Cardwell/Archive Photos.

Chapter Eleven Page 278, Universal City Studios; 278(t), Copyright 2001 byUniversal City Studios, Inc. Courtesy of Universal Studios Licensing, Inc. All rightsreserved.; 280(t), Dr. Mitsuo Ohtsuki/Photo Researchers, Inc.; 280(b), Nawrocki StockPhotography; 281, Corbis-Bettmann; 284, Stephen Maclone; 285(l), John Zoiner;285(r), HRW photo by Mavournea Hay; 287(t), Lawrence Berkeley National Lab; 291,Charles D. Winters/Timeframe Photography Inc./Photo Researchers, Inc.; 292,Superstock; 294, Nawrocki Stock Photography; 297, Fermilab National Laboratory;298, NASA Ames ; 299(t), Stephen Maclone; 299(b), Fermi National Lab/Corbis.

Chapter Twelve Page 300(tl), B.G. Murray Jr./Animals Animals/Earth Scenes;300(tr), Joe McDonald/Animals Animals/Earth Scenes; 300(bl), Dr. E.R. Degginger/Color-Pic, Inc.; 300(br), Richard Megna/Fundamental Photographs; 301(bl), IBM/Visuals Unlimited; 301(br), Bisson/Sygma ; 307(tr), Richard Megna/FundamentalPhotographs; 307(bl), Russ Lappa/Photo Researchers, Inc.; 307(br), Lester V.Bergman/Corbis-Bettman; 309(l,c), Dr. E.R. Degginger/Color-Pic, Inc.; 309(r), RichardMegna/Fundamental Photography; 310, Charles D. Winters/Photo Researchers, Inc.;311(l,c,r), Richard Megna/Fundamental Photographs; 312(tr), P. Petersen/CustomMedical Stock Photo; 312(tc), HRW photo by Victoria Smith; 313, David Parker/Science Photo Library/Photo Researchers, Inc.; 315(t), Phillip Hayson/PhotoResearchers; 316(t,c), Richard Megna/Fundamental Photographs; 316(b), Dr. E.R.Degginger/Color-Pic, Inc.; 317(t), Michael Dalton/Fundamental Photographers;317(b), NASA; 318(b), 320, Richard Megna/Fundamental Photographs; 323, Imagecopyright 2001 PhotoDisc, Inc.

Unit Five Page 324(b), Wally McNamee/Corbis; 324(b), Reuters/NASA/Archive;324(t), Archive France/Archive Photos; 325(t), James Foote/Photo Researchers, Inc.;325(r), Sygma; 325(l), Argonne National Laboratory/Corbis-Bettman.

Chapter Thirteen Page 326(b), Photri; 326(t), Jim Sugar Photography/Corbis;332(t), Kevin Schafer/Peter Arnold, Inc.; 332(l), HRW Photo by Peter Van Steen;335(r), Paul Silverman/Fundamental Photographs; 339(r), Calder Sculpture, NationalMuseum in Washington D.C. Photo © Ted Mahiec/The Stock Market; 340, 344, HRWphoto by Victoria Smith.

Chapter Fourteen Page 348(t), Romilly Lockyer/The Image Bank; 350(t), RobMatheson/The Stock Market; 350(br), Dorling Kindersley, LTD.; 351(tl), Charles D.Winters/Timeframe Photography Inc.; 351(tr), Richard Megna/FundamentalPhotographs; 351(br), Dr. E.R. Degginger/Color-Pic, Inc.; 354(b), HRW Photo byRichard Haynes; 355(r), Charles D. Winters/Photo Researchers, Inc.; 355(l), Mark C.Burnett/Photo Researchers, Inc.; 357(l,r), Michael Dalton/ Fundamental Photographs;358, Richard Megna/Fundamental Photographs; 359, Charles D. Winters/PhotoResearchers, Inc.; 360(l), Peticolas/Megna/Fundamental Photographs; 360(r), Richard

Credits 793

CR

ED

ITS

Megna/Fundamental Photographs; 361(c), HRW Photo by Peter Van Steen; 361(r),Tom Stewart/The Stock Market; 361(l), HRW photo by Victoria Smith; 364(t),364(bl), 364(br), Richard Megna/Fundamental Photographs; 365, Dorling Kindersley,LTD, courtesy of the Science Museum, London; 368(t), 369, Richard Megna/Fundamental Photographs.

Chapter Fifteen Page 372(b), SuperStock; 374(t), Yoav Levy/Phototake; 375(t,bl,br),376, Richard Megna/Fundamental Photographs; 377(b), Charles D. Winters/TimeframePhotography Inc.; 381(t), Runk/Schoenberger/Grant Heilman Photography Inc.; 381(b),Peter Arnold Inc., NY; 382, Miro Vinton/Stock Boston/PNI; 382(b), John Deeks/PhotoResearchers, Inc.; 386(br), Hans Reinhard/Bruce Coleman Inc.; 387, David M. Phillips/Visuals Unlimited; 388(br), Charles D. Winters/Timeframe Photography Inc.; 390, Runk Schoenberger/Grant Heilman Photography; 392(b), Charles D. Winters/Timeframe Photography Inc.; 392(t), Richard Megna/Fundamental Photographs; 394, Sygma; 395(t), Tom McHugh/Photo Researchers, Inc.; 395(b), Dennis Kunkel,University of Hawaii.

Chapter Sixteen Page 396(b), Dave Steel/NASA; 396(t), NASA; 398(b), HenriBecquerel/The Granger Collection; 398(t), Dr. E.R. Degginger/Color-Pic, Inc.; 403,Sygma; 405(b), Tim Wright/Corbis; 405(t), Custom Medical Stock Photo; 407, EmoryKristof/National Geographic Image Collection; 409(t), Shone/Liaison International;409(b), Michael Melford/The Image Bank; 410, Roger Rossmeyer/Corbis Bettmann;412(c), Dr. E.R. Degginger/Color-Pic, Inc.; 413, Emory Kristof/National GeographicImage Collection; 415(r), Science Photo Library/Photo Researchers, Inc.; 416(b),Sauder/Gamma Liason; 416(t), Cameramann International; 417(b), Charles O’Rear/Corbis ; 417(t), Courtesy of Micheal Atzmon.

Unit Six Page 418(b), Enrico Tedeschi; 418(t), AKG London; 418(c), Peter Southwick/AP Wide World; 419(b), Ilkka Uimonen/Sygma; 419(c), Enrico Tedeschi; 419(tl),Hulton Getty; 419(tr), property of AT&T Archives. Printed with permission of AT&T.

Chapter Seventeen Page 420(t), Norbert Wu; 420(b), Norbert Wu; 421(tr), NASA;421(tl), Corbis ; 421(br), ESA/Sygma; 421(bl), Anglo-Australian Observatory ;424(l,r), HRW photo by Victoria Smith; 426(b), HRW photo by Stephanie Morris;427(b), HRW Photo by Peter Van Steen; 429, Paul Katz/Index StockImagery/Picture Quest; 435(t), Patricia Ceisel/Visuals Unlimited; 435(b), David R.Frazier Photolibrary; 436, Takeshi Takahara/Photo Researchers, Inc.; 437, SciencePhoto Library/Photo Researchers, Inc.; 438(br), HRW photo by Richard Hanes; 439,Visuals Unlimited; 440(l), Richard T. Nowitz/Photo Researchers, Inc.; 445(t), PaulSilverman/Fundamental Photographs; 448(t), HRW photo by Victoria Smith; 450(t),Corbis-Bettmann; 450(b), Bill Ross/ Corbis; 451(l), Daniel Osborne, University ofAlaska/Detlev Ban Ravenswaay/Science Photo Library/Photo Researchers, Inc.;451(r), STARLab, Stanford University.

Chapter Eighteen Page 452(t), Photo Researchers, Inc.; 452(b), Courtesy Dr. AndreGeim; 453, HRW photo by Victoria Smith; 455(bl,bc,br), 456, Richard Megna/Fundamental Photographs; 461(l), Pekka Parviainen/Photo Researchers Inc; 463,SuperStock; 464, Tom Tracy/The Stock Shop; 478, The Image Bank; 479, HowardSochurek.

Chapter Nineteen Page 480(t), MZTV; 480(inset), Archive Photos; 488, Dr. E.R.Degginger/Color-Pic, Inc.; 489, Yoav Levy/PhotoTake; 493 (inset), Corbis Images;495(l), Corbis/Bettmann; 495(r), 501, SuperStock; 504, HRW Photo by Peter VanSteen.

Unit Seven Page 506(t), Fotos International/Archive Photos; 506(b), courtesy ofHughes Research Laboratories; 507(tl), David Parker/Science Photo Library/PhotoResearchers; 507(tr), Dr. E.R. Degginger/Color-Pic, Inc.; 507(c), Photofest; 507(br),HRW Photo by Victoria Smith; 507(bl), Brook/Gamma Liaison.

Chapter Twenty Page 508, AP/Wide World Photos; 511(t), Phil Degginger/Color-Pic,Inc.; 511(b), Emil Muench/Photo Researchers, Inc.; 512, Norbert Wu; 520(b), ErichSchrempp/Photo Researchers, Inc. ; 520, Don Spiro/Tony Stone Images; 522(tl,tr,),Richard Megna/Fundamental Photographs; 522(b), Richard Hamilton Smith/Corbis-Bettmann; 524(t), Richard Megna/Fundamental Photographs; 525, AP/Wide WorldPhotos; 526, Norbert Wu; 528, Richard Megna/Fundamental Photographs; 529,Martin Bough/Fundamental Photographs; 530, Pete Saloutos/The Stock Market; 531,Betty K. Bruce/Animals Animals/Earth Scenes.

Chapter Twenty-one Page 532(c), SuperStock; 532(t), The Granger Collection, NY;532(b), Mark Newman/Photo Researchers, Inc,; 538(c), Michael A. Keller/The PictureCube; 543(cl), Art Wolfe/ Tony Stone Images; 543(b), Tom Hannon/Picture Cube;544, Charles D. Winters/Timeframe Photography Inc.; 545, Dr. E.R. Degginger/Color-Pic, Inc.; 546, Stephen Dalton/Photo Researchers, Inc.; 547(b), Matt Meadows/PhotoResearchers, Inc.; 547(t), courtesy of Johann Borenstein; 550(b,c), Richard Megna/Fundamental Photographs; 553(l), 554(c), Image Club Graphics © 1998 AdobeSystems; 554(tl,tr,br), Bob Daemmrich/HRW Photo; 558, Ross Harrison Koty/TonyStone Images; 559, Dick Luria/Photo Researchers, Inc.

Chapter Twenty-two Page 562(t), Cindy Roesinger/Photo Researchers, Inc.; 562(b),Visuals Unlimited; 565, Photo Researchers, Inc.; 566, A.T. Willet/The Image Bank;567(r,l), Leonard Lessing/Photo Researchers, Inc.; 567(c), Michael Fogden andPatricia Fogden/Corbis; 568(l), Robert Wolf; 569(c), Hugh Turvey/Science PhotoLibrary/Photo Researchers, Inc.; 569(r), Blair Seitz/Photo Researchers, Inc.; 569(l),Leonide Principe/Photo Researchers, Inc.; 571(t), Bachmann/Photo Researchers, Inc.;571(b), The Stock Market; 572, Cameron Davidson/Tony Stone Images; 574, MichaelEnglish/Custom Medical Stock Photo; 577, Richard Megna/Fundamental Photographs;578, Robert Wolf; 579(t), Fundamental Photographs; 581(t), Robert Wolf; 581(b),HRW photo by Stephanie Morris; 583(t), Image copyright 2001 PhotoDisc, Inc.;583(c), Renee Lynn/Davis/Lynn Images; 583(b), Robert Wolf; 584, LeonardLessing/Peter Arnold, Inc.; 585, Index Stock Photography; 586, Leonard Lessing/Photo Researchers, Inc.; 587, Robert Wolf; 589(tr), Charles Winters/PhotoResearchers, Inc.; 589(cr), Mark E. Gibson; 589(br), Richard Megna/FundamentalPhotographs; 590(t,b), Dr. E.R. Degginger/Color-Pic, Inc.; 591, courtesy of theRaytheon Company.

Chapter Twenty-three Page 592(b), NASA; 592(t), Roger Ressmeyer/Corbis MediaWA; 594(b), Harry Rogers/Photo Researchers, Inc.; 594(r), Kindra Clinett/The PictureCube; 596, HRW Photo by Peter Van Steen; 597, Alan Schein/The Stock Market;598(tr), Yoav Levy/Phototake; 599(tr), HRW Photo by Stephanie Morris; 600(c),Richard Megna/Fundamental Photographs; 602, 603(b), Robert Wolf; 603(t,c), Dr.E.R. Degginger/Color-Pic, Inc.; 607(l,r), Leonard Lessing/Peter Arnold, Inc.; 612, Don

Mason/The Stock Market; 613(l,r), Ken Lax; 616, James L. Amos/National GeographicSociety; 618(b), US Patent and Trade Office; 618(t), Private collection of GarrettMorgan Family; 619(b), NASA; 619(t), SuperStock.

LabBook “LabBook Header”: “L,” Corbis Images, “a,” Letraset Phototone, “b” and“B,” HRW, “o” and “k,” images ©2001 PhotoDisc/HRW; 623(c), HRW photo byMichelle Bridwell; 623(br), Image copyright © 2001 PhotoDisc, Inc.; 624(cl), HRWphoto by Victoria Smith; 624(bl), HRW photo by Stephanie Morris; 625(tl), PattiMurray/Animals Animals; 625(tr), HRW photo by Jana Birchum; 625(b), HRW photoby Peter Van Steen; 626, HRW photo by Victoria Smith; 631, NASA; 638, 639(t),HRW Photo by Victoria Smith; 640, Stuart Westmoreland/Tony Stone Images; 644,Gareth Trevor/Tony Stone Images; 649, copyright 2001 Photo Disc/HRW Photo; 653, NASA; 662, HRW photo by Stephanie Morris; 663, Paul Dance/Tony StoneImages; 665(l,r), Robert Wolf; 670, 673, 676, HRW photo by Victoria Smith; 685, Rob Boudreau/Tony Stone Images; 687, 690, 697, HRW photo by Victoria Smith; 701, David Young-Wolf/PhotoEdit; 706, James H. Karales/Peter Arnold Inc., NY;709(t,c,b), 710, Richard Megna/Fundamental Photographs; 714, HRW Photo.

Appendix Page 727(t), 727(b), 731(b), HRW photo by Sam Dudgeon; 731(t), HRWphoto by Peter Van Steen; 748, HRW photo by Sam Dudgeon.

Sam Dudgeon/HRW Photo Page vii(tl,tr,br); xi,(bl); xiv(bl); xv(tr,tl); xvi(cl); xviii-xx;T6(tl,tr); T11(br); T12(bl); T15(tr); 2(cr); 5(b); 8(tl,tr); 9(bl); 12(t,c); 22(cl); 23(t);30(all); 31(l); 37(bl); 59(b); 61(bl); 64(r); 66; 76(b); 81(tr); 85(tl,tr,c); 87(r); 90(t);91(cl); 93(t); 94(bl); 96(t,b); 99; 100(b); 101(br); 106(tr); 107; 112(b); 114(b);116(t); 118(c); 124(bl); 132; 137(b); 157(r); 161; 177(t); 180; 182(b); 187(b);195(c); 198; 199(bl); 213; 215; 217; 220; 238; 240(t); 244-45; 251; 256; 279; 282-283; 303; 306; 307(c,tl); 308; 311(b); 312(tl,b); 315; 318(t); 336(b); 338; 339(l);345; 347; 349; 350(bl); 356; 373; 374(b); 378(b); 386(l); 388(t); 393; 397; 408;411; 431(b); 432; 438(t,bl,bc); 440(b,c); 445(b); 447; 449(b); 454; 455(t); 457;458; 460; 476-477; 480(b); 481; 482; 484-487; 490; 494-495; 496; 497; 500; 502;506(c); 509; 518; 527; 533(b); 535(b); 536; 538(r); 541(t); 550(t); 552; 556-557;563; 568(c); 588; 593; 594(l); 600(b); 611; 620(cl,t,b); 622; 623(b); 624(br,t); 628;630; 632-633; 634; 636-637; 639(b); 641; 643; 645-648; 650-652; 654-657; 659-661; 664; 675; 676; 677; 678; 681-684; 688; 692-694; 698-700; 702; 703-705; 707-708; 711; 713; 715; 717; 719-720; 723; 727; 731; 748; 723.

John Langford/HRW Photo Page v(cr); vi(tr); x(tl,bl); xii(br); xiii(tr,cl); T7(r); T8(bl);T12(tr); 6(l); 10(tl,c); 20(cl); 21; 22(tr); 28(b); 31(t); 35; 36(t); 37(t); 38-39; 41(b);42; 52(l); 54(all); 64(l); 91(bl,bc,br); 95(all); 145; 188-189; 191; 193; 195(t); 199(t);201(t); 205(tr); 206; 207; 208(b); 209(tr); 218(l); 219; 220(b); 223(b); 224; 226;233(cl,r,bl); 235(cr); 247; 252-255; 257; 258; 260-261; 264; 270; 301; 327-328;332(r); 336(t); 341; 348(b); 354; 355(c); 362-363; 368(b); 372(t); 377(t); 378(t);379; 388(bl); 389; 415; 421; 425; 426(tl,tr); 427(t); 431(t); 438(cl); 440(r); 441;442; 443; 444; 446; 448(b); 449(t); 524(b); 535(t);542; 543(t,bc); 553(r); 568(r);573; 576; 579(b); 582; 594(inset); 599(b); 600(tl); 601(b); 617; 623(t); 631(t);665(b); 666; 679; 691; 696.

Scott Van Osdol/HRW Photo Page T17(br); 61(br); 62(all); 63(b); 67(t); 69(b); 71-72; 163; 163: 166; 175(br); 194; 196; 199(br); 351(bl); 384; 385; 386(t); 391; 589;627; 629.


8th Grade Physical Science Textbook.pdf - Tuscaloosa County ...

Documents

Transcript of 8th Grade Physical Science Textbook.pdf - Tuscaloosa County ...