New Multimedia Modulesin CAEME CD-ROMSeries: Wave Motionand Mechanics

LAN YU,1 RAMEZ ATIYA,2 MAGDY F. ISKANDER,3 RICHARD W. GROW1

1University of Utah, Salt Lake City, Utah 84122

2Highland High School, Salt Lake City, Utah

3Unversity of Hawaii at Manoa, Honolulu, Hawaii 96822

Received 18 January 2002; accepted 20 July 2004

ABSTRACT: This paper presents two modules of multimedia lessons developed for the

center of excellence for multimedia education (CAEME) CD-ROM series. The first module is a

lesson on vibration and wave motion, and the other is concerned with lessons of mechanics.

The developed lessons contain several multimedia assets, i.e., text, graphics, audio, video,

movie, and animation. In developing these modules, emphasis has been placed on increasing

the interactivity, and hence is expected to be of broader use by seniors in high schools and

freshman in engineering. � 2005 Wiley Periodicals, Inc. Comput Appl Eng Educ 13: 72�83, 2005;

Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20032

Keywords: multimedia; wave motion; mechanics; CAEME

INTRODUCTION

Information technology (IT) is accelerating educa-

tional changes in our society and has become an

increasingly important component of the instructional

and learning experience in all fields and across all

types of instruction [1]. Web-based courses, distance

learning, and multimedia assets and interactive

courses are examples of these new educational

developments. Multimedia, an interactive use of a

combination of different media, such as text, graphics,

audio, video, and animation to impart information, is

one of the most effective approaches of computer-

aided instruction [2]. Multimedia assets provide an

avenue for improving the quality of education in many

respects. It has been successfully applied to all levels

of students, including primary, secondary, high

schools, and universities [3�21].

Multimedia-oriented computer technology mod-

els the natural phenomena and human behavior in

Correspondence to M. F. Iskander (iskander@spectra.eng.hawaii.edu).

� 2005 Wiley Periodicals Inc.

72

order to invent or to modify tools to support human

activities. Human activities are multimedia activities

and learning should not be a single-media activity

[22]. Educational multimedia technology has the

potential to improve the learning in several ways.

For example, multimedia has greater flexibility in

importing and delivering information. It provides the

information in the most convenient way to make it

attractive to students. Moreover, multimedia invites

students to navigate their own path and explore con-

nections among disciplines. The use of multimedia

technology also provides the opportunity for learning

experiences otherwise difficult to incorporate, for

example, using the virtual laboratories and simulation

studies that can be dangerous or unsafe [23].

Research on multimedia instruction that was

conducted by Reisman et al., has shown that students

who participated in the study outperformed students

in other sections by approximately one-half grade

[23]. Research at the California State University at

Northoradge showed that benefits from using com-

pute-aided technology in education, included incre-

ased students’ contact, improved attitude towards

math, and encouraged them to spend more time on

learning the subject [24].

To date, educators are aware of the challenges

and opportunities that arose with the wide available

high-performance computers on university campuses

and homes. Center of excellence for multimedia

education (CAEME) center, established in early 1990

by the National Science Foundation and IEEE, has

been active in stimulating and accelerating the appli-

cation of multimedia to help boost electromagnetic

education [25]. Its goal is to produce a curriculum that

supports the development of thinking, reasoning, and

collaboration skills throughout the engineering sci-

ence and math disciplines. Students learn by doing-

through participation in virtual laboratory, doing

virtual experiment, or conducting computer simula-

tions.

This paper, as the extension of multimedia

modules development in CAEME, describes two

lessons for college students. The first part is concerned

with the acoustic vibration and wave motion, while

the second part focuses on mechanics. Teaching expe-

rience shows that it is not easy for students to

understand the wave motion, especially the difference

between transverse and longitude waves. Using multi-

media techniques, abstract concepts can be easily

visualized and this makes the subject much more

understandable. To select suitable contents, several

textbooks were consulted and J. D. Cutnell and K. W.

Johnson’s book ‘‘Physics’’ is used as the principal

textbook [26]. The second part deals with mechanics,

which is a fundamental branch of physics and students

also face difficulties in understanding this subject. To

develop an attractive mechanics lesson, experiences in

high school teaching are exploited in the multimedia

development. The main topics of mechanics such as

kinematics, dynamics, energy, and momentum, are

developed in the lesson.

THE VIBRATION AND WAVEMOTION MODULE

The objective of the vibration and wave motion

module is to provide an introduction to the funda-

mental concepts and principles of vibration, wave

motion. Waves are everywhere in nature and our

understanding of the physical world is not complete

until we understand the nature, the properties, and

behaviors of waves. In this paper, we focus our

attention on mechanical waves, that is, waves that

travel only in material substances. The module is

divided into three sections: introduction to mechanical

waves, sound waves, and the superposition principle.

The following is a description of these components.

The Introduction Section

The goal of introduction section is to help students

develop mental models of waves and ultimately apply

those models to an understanding of one of most

common types of waves—sound wave.

In this section, all the basic concepts needed to

understand vibration and mechanical wave motion are

introduced. The concept of the mechanical wave, the

propagation mechanism, the difference between wave

phenomena, and illustrative examples are described.

Definitions of transverse, longitudinal, and the surface

waves are given accordingly.

After given the above basic description with some

real life examples, it is appropriate to show the

students how to describe waves mathematically. A

wave can be described by a variety of quantities, such

as amplitude, wavelength, frequency, time period,

speed, energy, and finally the propagation character-

istics of a wave can be described by an equation, i.e.,

the wave equation.

A wave simulation laboratory is developed to

show the student how the wave speed depends on the

medium through which it is moving. For example, an

alteration in the medium property causes changes in

the speed; the amount of energy carried by a wave is

related to its amplitude and, in turn, related to the

properties of the medium. The reflection, refraction,

and diffraction of waves are also briefly described.

NEW MULTIMEDIA MODULES IN CAEME CD-ROM SERIES 73

After these general descriptions of waves, a

specific case of mechanical waves was examined. In

this case, waves on a taut string are discussed and the

goal of this study is to describe what determines the

speed of a wave, and the characteristics of sinusoidal

waves as well as their mathematical description using

wavelength, period, angular frequency, and angular

wave number.

In this section of the lesson, the main multimedia

features are:

* Graphic animations are used to show the

difference between the transverse and long-

itudinal waves; a small movie clips shows water

waves movement, and a combination of the

transverse and longitudinal waves.* Graphic animations are used to show the basic

concepts describing harmonic waves and basic

wave properties such as wavelength, period,

amplitude, crest, trough, reflection, refraction,

diffraction, and interference.* A movie showing how to generate harmonic

waves on a continuous string by connecting one

end of a string to a blade that is, set onto vibration

is also included. Students are encouraged to

discuss the wave behavior when different bound-

ary conditions are present.

The Sound Waves Section

In the second section of this module, the ideas of wave

motion introduced in the first section are applied to

sound waves. Unlike the other physics modules, the

sound wave module naturally and inherently makes

good use of audio assets. The sound module demon-

strates how audio, when appropriately applied, enha-

nces the usability and functionality of an application.

Three topic areas for sound waves are discussed, that is,

the soundwave, theDoppler effect, and, the shockwave.

Sound Wave Concept. Sound is a mechanical wave

created by vibrating objects and propagate through a

medium from one location to another. It is pointed out

that in fluids, sound waves are longitudinal waves,

while in solids it may be longitudinal, transverse, or

neither. Like other waves, the speed of a sound wave

refers to how fast the disturbance is passed from one

particle to another. Typically, there are two essential

types of properties that affect the wave speed—the

inertial property and the elastic property. The density

of a medium is an example of an inertial property.

Elastic properties are those properties related to the

tendency of a material to either maintain its shape or

not deform whenever a force or stress is applied to it.

After the students learn how to calculate the

sound speed, other concepts were introduced includ-

ing: energy, sound frequency, and intensity.

The frequency of a wave refers to how often the

particles of the medium vibrate when a wave passes

through the medium. The ears of humans (and other

animals) are sensitive detectors capable of detecting

the fluctuations in air pressure that impinges upon the

eardrum. The sensations of these frequencies are

commonly referred to as the pitch of a sound. A high

pitch sound corresponds to a high frequency and a low

pitch sound corresponds to a low frequency. Figure 1

is a snap shot of a multimedia animation showing an

example of the application using sound frequency.

The amount of energy transported through a

given area of the medium per unit time is known as the

intensity of the sound wave. The greater the amplitude

of vibrations of the particles of the medium, the

greater the rate at which energy is transported through

it, and the more intense the sound wave is. The

mathematical relationship between intensity and

distance is sometimes referred to as an inverse square

relationship. Since the range of intensities that the

human ear can detect is large, the scale that is

frequently used by physicists to measure intensity is a

scale based on multiples of 10. The scale for

measuring the intensity of sound wave is the decibel

scale. The threshold of hearing is assigned a sound

level of 0 decibels (abbreviated 0 dB), corresponding

to an intensity of 10�12 W/m2. A sound that is ten

times more intense (10�11 W/m2) is assigned a sound

level of 10 dB.

Figure 1 Application of sound frequency: push-

button phone. When each of the phone buttons is

pressed, a pair of different tones is generated

simultaneously by the electric circuits. The tones are

transmitted to a digital display (right side) that shows

the frequency. [Color figure can be viewed in the

online issue, which is available at www.interscience.

wiley.com.]

74 YU ET AL.

Doppler Effect

The Doppler effect is observed whenever the source of

waves is moving with respect to an observer. A virtual

laboratory was created to allow students select the

relativemoving direction andmoving velocity and hear

the difference in sound according to Doppler effect.

Two applications ofDoppler effect are presented, one is

the radar gun and the other is the Doppler flow meter

used to measure the speed of red blood cells.

Shock Wave

If a source of sound is moving through a medium at

the speed faster than the speed of sound in the

medium, a different phenomenon called shock wave is

produced. In the developed module graphic anima-

tions are developed to show the wave front forms the

shape of a cone, with the source at its apex.

In summary, the main multimedia features inclu-

ding the sound waves section are as follows.

Movies:

* Show how a loudspeaker diaphragm produces

sound and why sound waves are longitudinal

waves.* Show the physics behind the human ears.* Show how sound waves carry energy: a vase

shattered by the sound of a passing by motor.* Show the variation of sound intensity in spherical

and plane waves.

Applications:

* The push-button telephone and the sound

frequency.* The ultrasonic rule: the sound speed in different

media.* Sonar: the sound speed in liquid.* The radar gun and the Doppler flow meter.

Virtual Laboratories:

* Doppler experiment.* Remember the notes.* The decibel intensity scale for some sources

allows the student to learn the different sound

intensity in real life.

Superposition Principle Section

The principle of superposition can be stated as

follows: when two waves interfere, the resulting

displacement of the medium at any location is the

algebraic sum of the displacements of the individual

waves at that same location.

There are two types of interferences, i.e., the

constructive interference and the destructive inter-

ference. Interference of sound waves has widespread

applications in the world of music. Music seldom

consists of sound waves of a single frequency played

continuously. Music is a mixture of sound waves that

typically have whole number ratios between the

frequencies associated with their notes.

A standing wave pattern is an interference

phenomenon. In this lesson, a video clip was produced

to show the standing wave effects. Another inter-

ference phenomenon is the resonance that happens

when one object is vibrating at the same natural

frequency as that of a second object and forces the

second object into vibration motion. The result is

always a large vibration and if a sound wave within

the audible range of human hearing is produced, a

loud sound is heard. A snap shot of an animation

illustrating the resonance effect is shown in Figure 2.

Finally, we focus on the application of mathema-

tical relationships and standing wave concepts to

musical instruments. Three general categories of

instruments have been investigated: string instruments

(which would include guitar strings, violin strings,

and piano strings), open-end air column instruments

(which would include the brass instruments such as

the flute and trombone and woodwinds such as the

saxophone and oboe), and closed-end air column

instruments (which would include the clarinet).

In this section of the lesson, the main multimedia

features are:

Animations:

* Standing wave patterns.

Figure 2 Sound laboratory that illustrates resonance

using resonant forks. [Color figure can be viewed

in the online issue, which is available at www.

interscience.wiley.com.]

NEW MULTIMEDIA MODULES IN CAEME CD-ROM SERIES 75

Applications:

* Physics behind a guitar, a flute, and a drum.* Beats and sound interference.

Simulation software:

* Wave interference simulation software package.

As a complementary component to this lesson, a

series of multiple choice quizzes and simple problems

are provided to test the student’s understanding of the

presented material. The overall content of the

vibration and wave motion lesson is presented in

Table 1.

THE MECHANICS MODULE

Mechanics is one of the most important and basic

branches of physics. It deals with the motion of

material objects. Two parts of mechanics are devel-

oped in the multimedia lessons, i.e., the kinematics

and the dynamics.

The Kinematics Section

Kinematics is the tool to describe motion of objects

using words, diagrams, numbers, graphs, and equa-

tions. The goal of any study of kinematics is to

develop sophisticated mental models, which serve us

in describing (and ultimately, explaining) the motion

of real-world objects. There are a variety of quantities

associated with the motion of objects—displacement

(distance), velocity (speed), acceleration, and time.

This section introduces the students to some of the

concepts used to describe motion; most important are

those of position, displacement, velocity, acceleration,

and the relationships between them.

Galileo first derived the equations for the position

and velocity of a uniformly accelerated object:

a ¼ constant

v ¼ v0 þ atð1Þ

x ¼ x0 þ v0t þ 12at2 ð2Þ

v2 � v20 ¼ 2aðx� x0Þ ð3Þ

where a is the acceleration, v is velocity, and x is the

displacement. Equation 1 gives velocity in terms of

time,Equation2gives thedisplacement in termsof time,

and Equation 3 gives velocity in terms of displacement.

To help students understand the relationship

among these three equations, a runway design pro-

blem was given as shown in Figure 3. In this example,

an airplane on an aircraft carrier starts at the runway

with a zero initial velocity and a maximum accelera-

tion. The airplane needs a minimum velocity to take

off. If the maximum acceleration of the plane is not

large enough, a very long deck (run way) is required

for the plane to gain the desired take-off velocity. To

solve the problem, designers mount a slingshot that

catapults the plane along the deck with huge acce-

leration. The students are asked to give the plane an

acceleration to achieve the take off velocitywith a given

length deck. Video clips and special sound effects were

also used to show the students the different results of

their designs.

A free-falling object is an object that is falling

under the sole influence of gravity. This definition of

Table 1 Contents of the Vibration and Wave Motion

Lesson

I. Introduction

1. Wave concept

2. Transverse, longitudinal, combination waves

3. Wave properties: reflection, refraction, diffraction

4. Wave on a string

* Mathematics description

* Velocity of waves

* Power and energy

5. Linear wave equation

II. Sound

1. Sound wave concept

* Overview

Application: push-button telephone

* Sound velocity in different medium

Application: ultrasonic ruler, sonar

* Sound energy, intensity, level

Decibel scale of sound source

Application: sensitivity of hearing

2. Doppler effect and shock wave

* Overview

* Doppler laboratory

* Application: radar gun, Doppler flow meter

* Shock wave

III. Principle of superposition

1. Constructive and destructive interference

2. Standing waves

* Transverse standing waves

Application: tuning guitar

* Longitudinal standing waves

Principle of flute

* Resonance

3. Beats

* Sound laboratory

4. Complex waves

IV. Simulation software

1. Interference simulation package

76 YU ET AL.

free fall leads to two important characteristics about a

free-falling object:

* Free-falling objects do not encounter air resis-

tance. This is why the ‘‘free falling’’ in the air is

not ‘‘free falling.’’* All free-falling objects (on earth) accelerate

downwards at a rate of approximately 9.8 m/s2.

One way to show the free falling experiment in a

multimedia lesson is by using video clips. This is

simply because animated pictures will give the student

the impression that the experiment is not real. In this

lesson, a video clip demonstrating the falling of

feather and cannon ball through vacuum was recorded

and used to help the students observe a real expe-

riment conducted at the University of Utah.

Describing the trajectory of a cannon ball was the

central problem of ballistics. With his free fall

equations, Galileo not only solved for the trajectory

of the cannon ball, he also solved the entire problem

of projectile motion when air resistance can be neg-

lected. The projectile motion is a two-dimensional

motion involving the combination of two independent

motions, one being the vertical motion described by the

free fall equations, and the other being the forward

motion with a constant speed. In the developed

multimedia module, an animation is used to show the

projectile motion and the emphasis is on the indepen-

dence of these two motions.

To illustrate the independence of the vertical and

horizontal motion, a ‘‘shooting the cougar’’ experi-

ment was recorded in the physics laboratory at the

University of Utah (see Fig. 4). A cannon ball and a

doll cougar were used in the experiment. The cannon

ball is expelled horizontally in the direction toward

the doll cougar, while the cougar is let down falling

toward the ground. Both cannon ball and cougar start

at the same height and with no downward velocity.

The cannon ball always hits the cougar because both

fall exactly in the same way, i.e., with the same acce-

leration (g), and they are always at the same height at

any instant.

After going through all these concepts, a Lab-

View simulation program was developed to help the

students gain hands-on experience. By adjusting

different initial velocities and angles, students are

able to measure the maximum height, flying time,

range of an object, and to watch the independent

motion in x, y axis, as shown in Figure 5. The software

also allows students to test their understanding of the

use of the kinematical equations to solve problems

involving the two-dimensional motion of objects.

The Dynamics Section

Dynamics is the most fundamental chapter in

mechanics. It is important that students understand

the concepts of force and mass and pay particular

attention to the relationship between the total force on

an object and its acceleration.

Newton’s first law states that an object in motion

remains in motion at a constant speed in a straight line

unless acted on by a force. An object at rest remains at

rest unless acted on by a force. To demonstrate this,

we set up two experiments. The first experiment

Figure 3 Application of Newton’s second law in the

design of a deck length in an aircraft carrier so that

aircrafts can take off safely at a given speed. [Color

figure can be viewed in the online issue, which is

available at www.interscience.wiley.com.]

Figure 4 ‘‘Shooting the Cougar’’ experiment is

recorded in the physics laboratories in the Department

of Physics at University of Utah. The experiment

illustrates the independence of the vertical and

horizontal components of motion of a projectile.

[Color figure can be viewed in the online issue, which

is available at www.interscience.wiley.com.]

NEW MULTIMEDIA MODULES IN CAEME CD-ROM SERIES 77

concerns with a ring sitting on an electromagnet.

When the magnet is switched on the ring is fired

upwards. The acceleration of the ring shows that there

is force acting on it. The second experiment shows a

deviation from a straight-line motion using the dis-

charge tube experiment. When the magnet is brought

close to the stream of electrons in a discharge tube, the

path bends. The magnetic field exerts a force on the

moving electrons and causes the change in the tra-

jectory.

According to Newton, an object will only

accelerate if there is a net or unbalanced force acting

upon it. The presence of an unbalanced force will

accelerate an object, i.e., changing its speed, or

direction, or both.

Newton’s second law of motion pertains to the

behavior of objects for which all existing forces are

not balanced. The second law tells us about how to

compute the acceleration, which is the central law of

classic mechanics. It states that the acceleration of an

object is dependent upon two variables—the net force

acting upon the object and the mass of the object.

Newton’s third law tells us something about

forces. A force is a push or a pull upon an object that

results from its interaction with another object. Forces

result from interactions.

Some forces result from contact interactions

(normal, frictional, tensional, and applied forces are

examples of contact forces) and other forces are the

result of action-at-a-distance interactions (gravita-

tional, electrical, and magnetic forces). If object A

exerts a force FBA on object B, then according to the

third law, the force exerted by object B on object A is

given by FAB¼�FBA.

The developed module also shows student how to

apply the Newton’s laws in real life. A snap shot of the

scenario is shown in Figure 6. We try to show what an

important role an infant car seat may play in a car

collision. Suppose that a young couple is taking their

5-kg baby for a drive. They have a collision during

which their car decelerate at 100 m/s2, if the baby is

held by the mother on her lap, according to Newton’s

first law, an object in motion trends to stay in motion

unless acted on by a force. Unless held by the mother,

the baby will keep going when the car is suddenly

stopped by the collision. According to Newton’s

second law, the force that will keep the baby moving

forward is ma¼ 5 kg� 100 m/s2¼ 500 N, the mother

needs the same amount of force, 500 N, to hold the

baby, which is 112 lbs. The mom better be very strong

to be able to achieve this. In bad collisions, the

acceleration can be three times as great as the one we

just described.

Another example involves applying Newton’s

second law in the physics of friction and antilock

brakes. The friction force is the force exerted by a

surface as an object moves across it or makes an effort

to move across it. The friction force opposes the

motion of the object. A surface may exert a frictional

force on an object that is in contact with it. Frictional

forces are classified as being either static or kinetic.

When the two objects are not moving relative to each

other, the friction force is labeled static friction. When

the surfaces are moving relatively to each other the

force is labeled kinetic friction. Static friction, the

friction that must be overcome to get an object mov-

ing, is greater than kinetic friction, which opposing

the motion of a moving object. The physics of friction

Figure 5 An example simulation running on the

projectile motion LabView program. [Color figure

can be viewed in the online issue, which is available at

www.interscience.wiley.com.]

Figure 6 A quiz designed to illustrate that the appli-

cation of Newton’s laws to show benefits from using

car seats for infants. [Color figure can be viewed in the

online issue, which is available at www.interscience.

wiley.com.]

78 YU ET AL.

is the basis for antilock brakes. When maximum force

is applied to the brake without allowing the tire to lock

in place, the static friction between the tires and road

is the maximum. Once the tires lock into place,

skidding begins and the friction between the tires and

the road becomes kinetic, which is much less than the

static friction, as the result, the friction provides less

acceleration and the car continues to slide farther. In

the quiz, the students are asked to calculate the

different distances the car covers before it finally stops

when it is equipped with a ABS or just skids from the

beginning (see Fig. 7).

TheWork, Energy, and Conservation Section

In this section, a different scheme will be utilized to

analyze the motion of objects. Motion will be appro-

ached from the perspective of work and energy.

Work and Energy. Mathematically, work can be

expressed by the following equation:

w ¼ f � d � cos�

where f is the force, d is the displacement, and � is theangle between the force and the displacement vector.

In other word, the work done on an object is defined to

be the component of the applied force parallel to the

direction of motion.

The second important term is kinetic energy.

When a net force acts on an object, its velocity incre-

ases according to the equation:

wfnet ¼1

2mv2f �

1

2mv2i

where vi and vf are the initial and final speeds of the

object. The term, 1/2(mv2), called the kinetic energy.

It can be seen that the kinetic energy of an object

is directly proportional to the square of its speed. As it

is often said, an equation is not merely a recipe for

algebraic problem solving, but also a guide to thinking

about the relationship between quantities. To help

students understand the presented material, a quiz was

included in this section.

The equation between work and velocity states

that when work is done on an object, it gains kinetic

energy. The work energy theorem has implication

toward artillery design. When a rifle is fired, the gas

from the burning powder does work on the bullet

giving its kinetic energy. Increase the length of the

barrel increases the work done on the shell and gives it

more kinetic energy. The big bertha with its very long

barrel was designed by German engineers to lob shells

across the English Channel.

There is an alternative to the work energy theo-

rem. An object high off the ground can be thought of

having stored or potential energy, in another word, an

object can store energy as the result of its position. As

it falls, it converts the stored potential energy into

kinetic energy. Potential energy is the stored energy of

position possessed by an object.

There are two forms of potential energy—

gravitational potential energy and elastic potential

energy. Gravitational potential energy is the energy

stored in an object as the result of its vertical position

(i.e., height). To determine the gravitational potential

energy of an object, a zero height position must first

be arbitrarily assigned. Typically, the ground is consi-

dered to be a position of zero height. But this is merely

an arbitrarily assigned position that most people agree

on. Gravitational potential energy has important

applications. In a dam, a huge mass of water, at a

great height stores an enormous amount of gravita-

tional potential energy. As the water passes through

turbines that drive electrical generators, gravitational

potential energy is turned into electrical energy.

Gravitational potential energy is important for all

roller coasters. The belt does work on the car, towing

it to the top of the track and giving it gravitational

potential energy. That potential energy is then

converted into kinetic energy as the car loses height.

The second form of potential energy is elastic

potential energy. Elastic potential energy is the energy

stored in elastic medium as a result of their stretching

or compressing. When an arrow is pulled back the

work done by the archer is converted into elastic

potential energy in the bow. When the arrow is rele-

ased, elastic potential energy is converted into the

kinetic energy of the arrow.

Physicists define the total mechanical energy of a

system as the sum of its kinetic and potential energy.

Figure 7 Applying Newton’s second law in the

design of antilock brake system. [Color figure can

be viewed in the online issue, which is available at

www.interscience.wiley.com.]

NEW MULTIMEDIA MODULES IN CAEME CD-ROM SERIES 79

Mechanical energy is the energy that is possessed

by a system due to its motion or its stored energy of

position. An object that possesses mechanical energy

is able to do work on another object. In fact, mecha-

nical energy is often defined as the ability to do work.

Numerous examples can be given on how an

object with mechanical energy can harness that energy

in order to apply a force to cause another object to be

displaced and show how energy can be converted from

one form to another. A classic example involves the

roller coaster car. As stated before when a roller

coaster car is displaced from ground level to the top of

the hill by a chain (driven by a motor), it gains

potential energy. When the car starts to roll down it

has no kinetic energy since the initial speed is zero. So

the total mechanical energy is pure potential. As the

car accelerates down the hill, it converts its potential

energy into kinetic energy and the car is now traveling

at high speed. The car will have its maximum velocity

and maximum kinetic energy at the bottom of the hill

where the potential energy is zero. As the car travels

up the next hill, it loses kinetic energy and gains

potential energy. Throughout its motion, the energy of

the roller coaster remains unchanged. Energy can be

neither created nor destroyed. A quantity that remains

unchanged is to be conserved.

This leads to the principle of conservation of

energy. Conservation of mechanical energy: in the

absence of friction, the total mechanical energy of a

system is conserved.

One of the examples that illustrate how external

force plays an important role in the motion can be

seen in skiers. The motion of skier is also governed by

the transformation of energy. As a skiers glides down

the hill, potential energy is transformed into kinetic

energy. If it can be assumed that no external forces are

doing work upon the skier as it travels from the top of

the hill to the completion, then the total mechanical

energy of the skier is conserved. To give student a

sense, a simple example is given. In the example, we

assume that friction and air resistance have a negli-

gible effect upon the skier’s motion and that the skier

never uses his poles for propulsion. So, the skier’s

total mechanical energy would never change during

the whole procedure. When the skier starts at the top

of a 1 km hill, he will gain some velocity at the bottom

of the hill. Simple calculation shows that the skier’s

speed at the bottom is 320 mph. This result is of

course ridiculous. In the realistic situation, the skier

experiences the force of friction and the force of air

resistance during the course of his motion. Both

friction and air resistance are external forces and both

do negative work and cause the total mechanical

energy to decrease during the course of the motion.

While the assumption that mechanical energy is

conserved is an invalid assumption here, the total

energy is still conserved. Most of the initial energy is

converted into heat through friction and air resistance.

In all these examples, we saw that energy is never

created nor destroyed.

The conservation of energy is one of the great

scientific discoveries. Bungee jumping dramatically

illustrates energy conservation. The jumper starts out

with gravitational potential energy. He converts it into

kinetic energy and into elastic potential energy stored

in the stretching bungee cord. As the stretch increases,

the kinetic energy and the gravitational potential

energy are converted into elastic energy. Through out

this process, some of the energy is converted into heat

through air friction and through heating the cord.

Eventually all the energy is converted to heat and the

jumper comes to rest. If there were no heat loss, the

bungee jumper would oscillate up and down forever.

Momentum and its Conservation. A massive object

moving at high velocity is said to carry great momen-

tum. Momentum depends upon variables such as mass

and velocity. In terms of an equation, the momentum

of an object is equal to the mass of the object times the

velocity of the object

momentum ¼ mass� velocity

The equation illustrates that momentum is

directly proportional to an object’s mass and directly

proportional to the object’s velocity. The standard

metric unit of momentum is the kg m/s.

Change in the momentum of an object requires a

net force acting overtime. Consider a ship, the engine

provides the forward force. The longer the time lasts,

the more momentum the ship gains. Because it is so

important, this product of force and time is given a

particular name. It is called impulse and is defined as

F �Dt. When an impulse is delivered to an object, the

momentum of the object changes by an amount equal

to the impulse.

The consequences of the impulse-momentum

theorem can be found everywhere. An example is as

follows. On March 23, 1989, the pilot of the Exxon

Valdez tanker realized that his ship was not heading

the right direction. The momentum carried the tanker

forward into Bligh Reef and the tanker hull was

ruptured (see Fig. 8). The impulse required to draw

the ship off its momentum was too great to stop the

ship in time. To see why this was such a problem, the

students are given a quiz in which to park a super

tanker. Suppose the student is the captain of a super

tanker. The student needs to bring 160,000 tons tanker

80 YU ET AL.

into dock. The engines produce 100,000 N of force.

How much time will you need to stop the ship and

how far will you travel in that time? By using the

impulse-momentum change equation, the time is

almost 2 h and the travel distance is 16 km. Based

on given force of the engine, it was impossible to park

the tanker in less time, and hence the environmental

disaster by Exxon.

The impulse-momentum theorem is the key to

understanding how a martial artist shatters a brick

(Fig. 9). A video was prepared to illustrate this

application. When watched in a slow motion, one may

note how the martial artist drops his weight and gains

momentum in a very short time (about 0.2 s). The

force on the martial artist is, therefore, very high. By

Newton’s third law, the force on the martial artist’s

hand is equal and opposite to the force on the brick.

Thus the martial artist is able to break the brick beca-

use of the huge force generated when his momentum

is abruptly changed.

Other examples such as the invention of the

stirrup are given to provide illustrations of the impulse

momentum theorem. One of the most useful con-

sequences of the impulse momentum theorem is the

law of the conservation of momentum. The momen-

tum of an isolated system is always conserved. By

‘‘isolated’’ we mean that no external forces act on the

system.

A device that uses the principle of momentum

conservation is the bat. When a bat swung at 80 mph is

slowed to 40 mph in its collision with the ball, the bat

loses half its original momentum. That momentum

is not lost. It is transferred to the ball. Because the bat

is so much more massive, the momentum transfer is

enough to stop a 90 mph ball and send it flying back at

90 mph (see Fig. 10).

Momentum conservation is the basis of pool. A

video clip is produced to show how all the momentum

of the queball is transferred to another ball.

Sometimes conservation of momentum is a

problem as is the case with artillery. A loaded-cannon

has zero momentum. When fired, the shell carries

forward momentum. The cannon recoils backwards

with equal and opposite momentum. The result is the

Figure 8 The oil spilt of Exxon Valdez tanker at

Alaska in 1989. When the pilot realized that his ship

was not heading the right direction. The momentum

carried the tanker forward into Bligh Reef and the

tanker hull was ruptured. [Color figure can be view-

ed in the online issue, which is available at

www.interscience.wiley.com.]

Figure 9 The impulse-momentum theorem is the key

to understanding how a martial artist shatters a brick.

[Color figure can be viewed in the online issue, which

is available at www.interscience.wiley.com.]

Figure 10 An illustration of the law of the conserva-

tion of momentum in the baseball. [Color figure can

be viewed in the online issue, which is available at

www.interscience.wiley.com.]

NEW MULTIMEDIA MODULES IN CAEME CD-ROM SERIES 81

total final momentum is still zero, i.e., momentum is

conserved. Various strategies have been used to

absorb the recoil. Modern cannons are equipped with

shock absorbers. In the past, special trenches were dug

from where cannons are fired. Even special ramps

were sometimes built to absorb recoil. Without doubt,

however, the most important applications of momen-

tum conservation are the jet plane and the rocket. A jet

plane engine takes low-velocity air and expels it at

huge speed. The air gains backwards momentum and

the plane recoils forward. The plane of course

experiences the retarding force ‘‘air resistance’’ and

the forward momentum is balanced by the friction

exerted by the air. The result is a plane cruising at a

constant speed. Like the jet plane, a rocket is also

recoil driven. Exhaust is driven out the back at huge

speed and the rocket recoils forward. Since a rocket

must be able to operate in space and there is no air

resistance in space, a rocket can gain enormous

velocity in space.

The content of the mechanics lesson is presented

in Table 2.

DISCUSSION AND CONCLUSIONS

It is shown that the multimedia techniques, when

used properly, can provide the environments sug-

gested by the constructivism of education. These

environments, including visual, audio, and animated

ones, will improve the education process in many

respects.

In this paper, two modules of multimedia lessons

were developed. The first one is the vibration and

wave motion module and the second is the mechanics

module. In the development of these modules, efforts

were made to extensively use the state-of-the-art

multimedia technology. Rich environments, including

visual, audio, and animation were created and

advanced programming languages were employed to

develop more complex concepts when necessary. In

these modules, fundamental knowledge, logical

development of the theory, useful experiments, and

problems for practicing were all presented via multi-

media tools. It should be pointed out that in the

development of the mechanics module, an experi-

enced physics teacher is consulted for the story

boarding and video recording. This certainly

enhanced the quality of the developed lessons.

It should be noted that the development of

multimedia instruction is expensive and heavily

dependent on the computer technology. It also involves

cooperation among experts from different disciplines

and thus is a complicated development.

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Table 2 Contents of the Mechanics Lesson

I. Kinematics

A. Motion in one dimension

* Motion with constant acceleration

Application: design runway for aircraft carrier

* Free fall

LabView simulation program

B. Motion in two dimension

* Motion with constant acceleration

* Projectile motion

Application: shooting the cougar

Application football kickoff

LabView simulation program

II. Dynamics

A. The concept of force

B. Newton’s first laboratory

* Video clips of electromagnet ring and discharge

tube

C. Newton’s second law

D. Weight

E. Newton’s third law

F. Applications

* Infant car seat safety

* Unsuccessful vanguard launch

* Forces of friction and antilock brake systems

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* Application: gas saving policy set by the US

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* Elastic potential energy

Application: archery

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F. Momentum and its conservation

* The impulse momentum theorem

Applications: Exxon oil spilt in Alaska

& Martial arts

& Invention of stirrup

* The law of the conservation of momentum

Applications: baseball bat

& Rocket propulsion

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BIOGRAPHIES

Lan Yu received the MS degree in computer science from

Chongqing University, China. She also received the MS degree in

electrical engineering from University of Utah. She is currently

working with RTSI, Utah.

Ramez Atiya received the MS degree in physics and his PhD in

philosophy from University of Utah in 1972 and 1976, respectively.

He is currently teaching in Highland High School, Salt Lake City,

Utah.

Richard W. Grow received his PhD degree

in electrical engineering from Stanford Uni-

versity in 1955. He is the director of

Microwave Device and Physical Electronics

Laboratory and the codirector of Center for

Advanced Computer-Aided Science and

Engineering Education, Electrical and

Computer Engineering Department, Univer-

sity of Utah.

Magdy F. Iskander is the director of the

Hawaii Center for Advanced Communica-

tions (HCAC), College of Engineering,

University of Hawaii at Manoa, in Honolulu,

Hawaii. He was a professor of Electrical

Engineering and the Engineering Clinic

Endowed chair professor at the University

of Utah for 25 years. He was also the director

of the Center of Excellence for Multimedia

Education and Technology. From 1997 to 1999, he was a program

director in the Electrical and Communication Systems Division at

the National Science Foundation. His ongoing research includes

phased array antennas, microwave processing of materials, and

propagation modeling for wireless communications.

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