Friction Stops Motion - Delta Education

BROWARD COUNTY ELEMENTARY SCIENCE BENCHMARK PLAN

Grade 3—Quarter 3Activity 24

SC.C.1.2.1The student understands that the motion of an object can be described and measured.

SC.H.1.2.1The student knows that it is important to keep accurate records and descriptions to provideinformation and clues on causes of discrepancies in repeated experiments.

SC.H.1.2.2The student knows that a successful method to explore the natural world is to observe andrecord, and then analyze and communicate the results.

SC.H.1.2.3The student knows that to work collaboratively, all team members should be free to reach,explain, and justify their own individual conclusions.

SC.H.1.2.4The student knows that to compare and contrast observations and results is an essentialskill in science.

SC.H.3.2.2The student knows that data are collected and interpreted in order to explain an event orconcept.

ACTIVITY ASSESSMENT OPPORTUNITIES

The following suggestions are intended to help identify major concepts covered in the activitythat may need extra reinforcement. The goal is to provide opportunities to assess studentprogress without creating the need for a separate, formal assessment session (or activity) foreach of the 40 hands-on activities at this grade level.

1. Ask students to describe situations when friction is helpful and to explain why. (Answerswill vary. Examples: Friction stops things from sliding, so car tires have friction with theroad. We need friction when we walk.)

2. Use the Activity Sheet(s) to assess student understanding of the major concepts in theactivity.

In addition to the above assessment suggestions, the questions in bold and tasks thatstudents perform throughout the activity provide opportunities to identify areas that mayrequire additional review before proceeding further with the activity.

Friction Stops MotionFriction Stops Motionac

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broward county hands-on science Quarter 3 249

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250 activity 24 Friction Stops Motion

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OBJECTIVES

Students discover that friction is a force thatresists motion.

The students

� observe the effects of friction on a movingobject

� discover how lubrication reduces frictionbetween an object and the surface overwhich it moves

� suggest additional ways to reduce frictionbetween objects

SCHEDULE

About 30 minutes

VOCABULARY

frictionlubricant

MATERIALS

For each student

1 Activity Sheet 24, Parts A and B

1 pr safety goggles*

For each team of two

1 container, plastic

1 push-pull meter

1 ruler, dual-scale*

1 set washers, stacked and taped (from Activity 23)

For the class

1 btl detergent, liquid

1 measuring spoon, Tbsp.

1 mixing bowl*

2 rolls paper towels*

water (preferably access to a sink)*

Delta Science Reader Force andMotion

*provided by the teacher

PREPARATION

Make a copy of Activity Sheet 24, Parts Aand B, for each student.

Before class, dilute some liquid detergentin a bowl by mixing one part soap to twoparts water. Pour about 3 Tbsp. of themixture into each plastic container, onecontainer per team of two.

Each team of two will need a push-pullmeter, a stack of washers (taped, fromActivity 23), a plastic container withdiluted detergent, a ruler, and some wetand dry paper towels for wiping off theirhands and desktops.

BACKGROUND INFORMATION

Students know that in order to get an object tomove, force must be applied to the object. Buta moving object will not remain in motionforever. There are other forces acting on it thatcause it eventually to slow down and stop. Onesuch force is gravity. Another force is friction.

Friction is a force that resists motion. Frictionoccurs whenever two objects rub against eachother. The surfaces of all objects, no matterhow smooth they may appear, contain tinybumps and pits that cause the objects to

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“catch” as they slide past one another.Such resistance slows the objects down,generates heat and noise, and can causethe surfaces of the objects to wear.

Friction makes work harder because itincreases the amount of force necessary tomove an object and keep it in motion. Therougher the surface of the object, thegreater the friction produced. The greaterthe friction, the more force needed to movethe object. If the friction is stronger thanthe force that is applied to the object, theobject will not budge.

One way to reduce friction between twoobjects is to apply a layer of lubrication tothe surfaces that touch. Lubricants aresubstances that reduce friction betweensurfaces by smoothing over the bumps andpits in the surface, allowing the objects toslide across each other with less resistance.

In this activity, students will observe theeffects of friction—and lubrication—onmoving objects.

Friction Stops Motion1. What did you feel when you rubbed your hands together?

a. What did you hear?

b. What caused this?

2. You applied motion lotion to your hands and rubbed them together. What didyou feel?

3. Motion lotion is a kind of lubricant.

What are lubricants used for?

4. Use your push-pull meter to slide yourwashers as shown. How far will your stack of washers move? Record yourresults. Did you use lubrication? Write yes or no.

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Amount ofForce

6 units

8 units

6 units

Distance Moved

Did You Use Lubrication?

8 units

(The chemical used in this activity is liquiddetergent.)

palms felt warm

a swishing sound

friction

It was easier to rub hands together; palms did not

heat up.

to reduce friction

about 61/2 inches

about 8 inches

about 13 inches

about 16 inches

no

no

yes

yes

Distances will vary depending on the smoothness of thedesktop surface.

Activity Sheet 24, Part A

�

Friction Stops Motion

5. How did using lubrication change your results?

6. What are two ways to get an object to move farther?

a.

b.

7. What are some good lubricants? Why?

8. What are some other ways to reduce friction between moving objects?

Adding motion lotion to the desktop reduced the

friction between the stack of washers and the

desktop, which caused the stack to travel farther

with the same force.

apply more force to the object

reduce friction between the object and the surface

over which it moves

Answers will vary: oil, soap, petroleum jelly, hand

lotion—because they are slippery

Possible answer: using wheels or cushions of air or

magnets

Activity Sheet 24, Part B�

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Additional Information

Ask students to demonstrate what they dowhen their hands get cold.

Ask students, How does rubbing your handstogether help?

Have all students rub their hands togethervigorously for 10 to 15 seconds. Ask them tonotice what they feel and hear. Ask, Whatcauses this?

Write the word friction on the board and readit aloud. Tell students that friction occurswhenever two surfaces rub together.

Explain that all objects, no matter howsmooth they look, contain tiny bumps andpits in their surfaces that cause the objects toscrape and snag as they slide past eachother. This resistance to movement is calledfriction.

Distribute a copy of Activity Sheet 24, PartsA and B, to each student. Tell students tocomplete question 1, parts a and b.

Divide the class into teams of two. Distributea plastic dish with some diluted detergent init to each team. Tell students that you callthis substance “motion lotion.”

Ask, What do you think this substance does?

Tell students to dip their fingers in the motionlotion and spread a generous amount on thepalms of their hands. Then have them rubtheir hands together like they did before. Ask, What do you feel now?

Write the word lubricant on the board.Explain that the motion lotion acts like alubricant to reduce friction. Lubricants areslippery substances that coat and smooth thesurfaces of objects so that the objects slideacross each other more easily.

Some students will blow on their hands, butothers will rub them together.

Students will probably say that it makes themfeel warm.

Students will probably say the rubbing.

Students may suggest that it helps thingsmove better.

Students should feel no heat this time.

Guiding the Activity

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2Safety Note: Caution students to handlethe motion lotion carefully. Wipe up spillsimmediately to prevent slips and falls.

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Have students wipe their hands off with a wetpaper towel (or rinse them in a sink) and drythem. Tell them to complete questions 2 and3 on their activity sheets.

Then tell students that in this activity theyare going to observe the effect of friction—and lubrication—on a moving object.

Distribute a push-pull meter, a stack ofwashers, and a ruler to each team. Refillstudents’ dishes with motion lotion asnecessary.

Tell students to place their push-pull metersflat on their desk, with the handle closest tothem. Have them place the stack of washerson the desk against the rubber band, pull thestack back against the band to 6 units offorce (like a slingshot), then release the stackso it slides along the desktop (see Figure 24-1).

Tell students to use their ruler to measure thedistance that the washers traveled and torecord the distance in the table of question 4on Activity Sheet 24, Part A.

Ask, How far did your stack of washers slide?

Ask, What keeps the stack of washers fromsliding any farther?

The stack should slide forward, between thearms of the push-pull meter.

Answers will vary. For most teams, the stackof washers should slide across the deskabout 14 cm (6 1⁄2 in.).

Students may say that the washers “ran outof force.” Guide students to understand thatfriction between the washers and thedesktop slows the motion of the washersuntil they stop.


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� Figure 24-1. Using the push-pull meter to apply 6 units of force to a stack of washers.

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Ask, What can we do to make the stacktravel farther?

Have students repeat the experiment, thistime using 8 units of force. Tell them tomeasure the distance that the stack travelsand to record the distance in the table ofquestion 4 on Activity Sheet 24, Part A.

Then ask, How can we get the stack totravel farther without using any more force?

Have students dip their fingers in somemotion lotion and spread a thin track alongthe projected path of the stack of washers.Have them also dip the stack of washers intothe liquid, then repeat the experiment using 6units of force, followed by 8 units of force.Tell them to measure the distance that thestack of washers travels each time and torecord the distances in the table of question4 on Activity Sheet 24, Part A.

When students have finished, ask, How fardid the stack of washers travel each time?

Ask, What caused the stack to slide farther?

Ask students to answer questions 5 and 6 onPart B of their activity sheets.

To conclude, ask, How does lubricationreduce the amount of force needed to movean object?

Tell students to complete question 7 on theactivity sheet. Have volunteers read theiranswers aloud.

Students may suggest applying more force.Accept all answers.

Students should find that the stack travelsslightly farther with 8 units of force.

Students may suggest reducing friction byusing lubrication on the bottom of thewashers. Accept all reasonable answers.

The stack should slide about twice as far as itdid without lubrication.

The motion lotion acted as a lubricant toreduce friction between the desktop and thewashers, enabling them to remain in motionlonger and thereby travel farther.

Lubrication works by reducing frictionbetween two surfaces, allowing the surfacesto slide past each other more easily.


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Tell students that lubricating fluids—primarily oil—are often used in machines toreduce the friction between moving parts.This makes the machines work moreefficiently, more quietly, and at a coolertemperature. But it is not always possible orpractical to use lubricants when you want tomove things.

Ask, What are some other ways to reducethe friction between moving objects? Tellstudents to answer question 8 on theiractivity sheets.

Tell students that in the next activity, they aregoing to learn about one of the mostimportant inventions in history—the wheel—and how it can be used to overcome friction.

As appropriate, read or review page 15 of theDelta Science Reader Force and Motion.

Some students may suggest using wheels,cushions of air, or even magnets. Accept allanswers, and review them as a class.


REINFORCEMENT

Challenge students to find out how muchforce they need to use to get the washers totravel 14 cm (6 1⁄2 in.) with lubrication.(Answer: Students should discover that withlubrication the stack can be moved 14 cmusing about half the force that they neededwithout lubrication—probably about 3 unitsof force instead of 6.)

SCIENCE JOURNALS

Have students place their completed activitysheets in their science journals.

CLEANUP

Give students wet paper towels and havethem wipe their desks clean. Collect thepush-pull meters, stacks of washers, anddishes of motion lotion (soap). Rinse and drythe stacks of washers and dishes and returnthem, along with the measuring spoon andbottle of liquid detergent, to the kit.

SCIENCE AT HOME

Point out that the soles of our shoesprovide friction between our bodies andthe surfaces we walk on. Show studentshow to do a sole imprint: cover the shoesole with a piece of paper and rub over itlightly with a pencil to reproduce thepattern. Then invite them to compare thesoles of family members’ shoes and bringin to class a rubbing of the sole they thinkwill provide the most friction.

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Connections

Science ChallengeTell students that in many sports, athleteswant to increase friction to prevent sliding orslipping. For example, baseball pitchers rubrosin on their hands to increase friction andimprove their grip on the ball. Challengestudents to brainstorm examples of othersports in which friction plays an importantrole. (Students might mention the sandpaperor rough rubber covering on a table tennispaddle, grooved soles on running shoes,rosin on gymnasts’ hands, and wax on cross-country skis.)

Science ExtensionObtain an ice cube and a blunt knife. Tellstudents that you will try to cut through thecube, first by simply pressing down on theknife and then by sawing back and forth withit. After you have done this, ask: Whichmethod was more successful? Why? (Sawingwas more successful, because the friction ofthe knife against the cube creates heat thatmelts the ice.) You may want to tell studentsthat ice skaters are actually skating on a thinfilm of water that the skate blades melt asthey glide across the ice.

Science and the ArtsAsk a student, teacher, or parent who plays abowed instrument such as a violin todemonstrate for the class how it is played.Explain that the sound production dependson friction between the bow and the stringsand that the musician applies rosin to thebow to increase the friction.

Science and Language ArtsAsk students to think about what everydaylife would be like if friction did not exist.Simple activities such as walking and writingwould be impossible. Bicycles, cars, andother wheeled vehicles would not work

because the wheels would spin withoutgripping the road surface. Encourage studentsto write poems, short stories, or humorousskits about life in a frictionless world.

Science and MathHave teams of students carry out thefollowing activity to measure the forcerequired to overcome friction under variousconditions. With strips of masking tape, markstarting and stopping lines at least one foot(30.48 cm) apart on a desk. Students can usethe stack of washers from the activity oranother object as a load. They then use thepush-pull meter to pull the load from thestarting line to the stopping line, recordingthe force of the pull that is required. Thenrepeat the experiment with the desk surfacecovered with different materials, such asaluminum foil, sandpaper, smooth fabric,terry toweling, waxed paper, and waxedpaper coated with a thin film of motion lotion(diluted detergent). Record the results ofeach trial. When students have completedtheir experiment, help them make a bar graphshowing the results. Have them label thehorizontal axis Type of Surface and thevertical axis Average Units of Force.

Science, Technology, and SocietyTell students that scientists’ discoveriesabout friction have led to attempts to improvetransportation by reducing friction betweenthe vehicle and a surface. Two examples areair cushion vehicles, or ACVs (also known ashovercraft), and hydrofoils, which havespecial fins that lift the craft above the waterwhen speed is attained. Encourage studentsto research these vehicles and report theirfindings to the class.

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Friction Stops Motion - Delta Education

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