Have you ever done the wave at a baseball game? That undulating motion pro-duced by spectators standing, one after another, in sequence reminds us of themotion of waves in nature. Waves are difficult to see because most of them areinvisible. But like the wave at a baseball game, the energy in waves moves fromone place to another.

If you drop a marble into a pool of water, you create a wave. The marble haskinetic energy because it is moving, and it transfers some of this energy to thewater particles, causing them to move. The particles of water transfer this ener-gy to adjacent particles, and the wave moves outward from the center.

A Disturbance

A wave is a disturbance that moves energy through matter or space. The mat-ter or space through which a wave moves is described as the medium. Air is a medi-um for sound waves. Light waves do not need a medium because they can travelthrough a vacuum. As a wave travels through a medium, the medium does notmove along with the wave. Only the energy is transmitted. To see this, tie a stringto a doorknob, and move it up and down to form a wave (see Figure A). The stringis not moving toward the doorknob, but energy is moving along the string. The wavemoves from your hand to the doorknob. But the medium, a string in this case,moves up and down.

FIGURE A

49

!.1

..;LESSON 5: WAVE ENERGY

I.

5-1 WAVEON iiII..

.... Content on Wave Energy I..-

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What Wave?

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50 5-1 Wave On

Transverse and Longitudinal Waves

There are two types of waves: transverse and longitudinal. An ocean wave is atransverse wave because the medium (the ocean) moves at right angles to thewave. Just like the string you tied to a doorknob, the ocean moves up and down,but the wave moves toward the shore. The crest of a transverse wave is the highpoint, and the trough is the lowest downward point (see Figure B).

Crest Crest

Trough Trough

FIGURE B

In longitudinal waves, the medium moves back and forth in the same direc-tion as the wave travels. Ask a friend to hold one end of a Slink~. When you pushyour end of the Slink~ in and out, you are creating a longitudinal wave. Particlesof the medium are compressed or pushed together in areas called compressions.As a compression moves forward, it leaves behind a space containing fewer par-ticles, called a rarefaction. Sound wave'Stravel in this manner.

Wave Characteristics

There are many types of waves: sound waves, light waves, radio and televisionwaves. All waves have some common characteristics.

Amplitude. This characteristic refers to the maximum distance molecules ofthe medium are displaced from their original position. If you push the Slink~ verygently, the waves you create will have a small amplitude. However, if you shove theSlink~ forward with a lot of force, you can create waves with large amplitudes.

Wavelength. All waves are measured by wavelengths. A wavelength is thedistance between two consecutive crests or between two successive identical waveparts. Wavelength is usually measured in meters or centimeters. However, wave-lengths of light are measured in millionths of a meter (micrometers).

Frequency. The number of waves that pass a point per unit of time is calledfrequency. For example, if 1000 complete waves passed a point in one second, thewaves would have a frequency of 1000 cycles per second. Wave frequency is mea-sured in units called hertz (Hz). A frequency of 1 Hz is equal to one wave per sec-ond. Higher frequencies are measured in kilohertz (kHz), and extremely high

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9 780876 287514

5-1 Wave On 51

frequencies are measured in megahertz (MHz). AM radio waves are broadcast inkilohertz, but FM waves are broadcast in megahertz. If a station is 104 MHz onthe FM radio, it is broadcasting waves with a frequency of 140,000,000 hertz.These waves are produced by electrons vibrating at the same frequency in theradio station's transmitting antenna.

Sound

Sounds are produced by vibrating objects that cause the surrounding medium,air, to vibrate. The speed of sound in air is about 340 meters per second. You candetermine how far you are from a bolt of lightning by counting the number of sec-onds between the time you see the lightning and the time you hear the thunder.Multiply the number of seconds between the lightning and the sound of thunderby 340 meters, and you know how far you are from the storm. Thunder is a com-pression of air molecules caused by the heat of the lightning bolt. Light travelsabout a million times faster than sound, so the light from the lightning bolt reach-es your eyes almost instantly.

Sound has two important components.Intensity. The amount of energy in a sound wave is referred to as that

wave's intensity. Intensity determines the loudness of a sound, and is measuredin units called decibels. The decibel scale begins at zero, the point at which wecan just hear. The sound of a rocket engine is deafening and is 200 on the decibelscale. All sounds with intensities near 120 decibels can cause pain to humans.Sounds above 85 decibels can damage hearing. Loud music, especially playedthrough earphones, damages many people's hearing.

Pitch. Sound waves also have pitch, which is determined by how fast themolecules of the medium are vibrating. The frequency of a sound wave deter-mines the pitch of a sound. High-frequency sound waves have high pitches. Ahigh note by a female singer may be about 1000 Hz, and a male bass may sing at70 Hz. Humans can hear sounds between 20 Hz and 20,000 Hz. Ultrasonicsounds are those waves whose frequencies are above 20,000 Hz. Dogs can hearpitches up to 25,000 Hz, and porpoises can hear them up to 150,000 Hz. Somebats produce their own ultrasonic frequencies, which they use for navigation.

The Doppler Effect

Have you ever listened to the sound of a siren approaching you? The pitch of thesiren gets higher as it approaches you due to the Doppler effect. When there ismotion between the observer and the source of sound, the frequency of soundwaves changes. As the sound approaches the observer, the waves are compressedcloser together, and waves reach the observer sooner than they would have if thesource of sound had not been moving. Therefore, sound waves that reach theobserver seem to have a higher pitch because their frequency has increased. Asthe source of sound moves away from the observer, the sound waves are fartherapart, and the pitch drops.

'-

Name Date (5-1)

WAVES--VOCABULARY ACTIVITY FOR

WAVE ON

Select a word from the wave below that fits in the following sentences. Some words can beused twice.

wave amplitude batsmedium rarefraction hertz intensitytransverse compression frequency sound

longitudinal trough Doppler decibelscrest ultrasonic

1. The of a sound wave determines a sound's pitch.

2. Ocean waves are

at right angles to each other.

waves because the water and the waves move

3. In a longitudinal wave, the space where there are few particles of medium is called a

4. Some_

gational purposes.

can produce ultrasonic sounds, which they use for navi-

5. A is a disturbance that moves energy through space or matter.

6. Sound is a wave because the medium moves back and forth in

the same direction as the wave travels.

7. The of a transverse wave is the highest point, or point of max-

imum displacement, of the wave.

8. The sound of an approaching train whistle increases in pitch because of theeffect.

9. Sounds that people cannot hear are called sounds.

10. Air is one through which sound can travel.

11. The frequency of sound waves is measured in units called

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VOCABULARY AcTIVITY(continued)

12. In a sound wave, the space where air particles are pushed together is called a

13. A_

moleculesto vibrate.wave is produced by a vibrating object that causes the air

14. The intensity or loudness of a sound is measured in units called

15. Wave

displaced.refers to the maximum distances medium molecules are

16. The lowest displacement of a wave is called the wave's

17. A rocket engine produces a wave of highthe decibel scale.

, which registers 200 on

18. Dogs can hearsounds in the 25,000-Hz range.

19. FM radio stations broadcast at frequencies in the mega- range.

20. Sounds above 85can damage our ears.

53

Name Date (5-2)

GoOD VmRATIONS

Lab on Wave Energy

Introduction

A sound is considered music if it has a pleasing quality, an identifiable pitch, and a repeat-ed timing or rhythm. People have made musical instruments for centuries. Woodwindinstruments such as flutes and clarinets produce their sound by vibrating a column of airwithin the instrument. Drums and other percussion instruments vibrate when they arestruck. Stringed instruments vibrate when they are either rubbed or plucked. Guitars, vio-lins, and pianos produce sounds when their strings are vibrated. The pitch of a stringedinstrument can be changed by changing the length, tightness, or thickness of the string.

A short string vibrates at a higher frequency than a long one and thus produces ahigher pitch. Musicians change the pitch of a string by placing their fingers along it, thusaltering its length. A finger placed near the far end of a string shortens it slightly, raisingthe pitch one or two steps. A finger placed near the center of an instrument shortens thestring much more, producing a very high pitch.

The tighter a string, the higher the frequency of its vibration. Pianos, guitars, and vio-lins are tuned by tightening or loosening the strings. When a string is tightened, it pro-duces a -higher pitch.

Thick strings vibrate slower, and thus at a lower frequency, than thin strings. Thestrings on a bass guitar are much thicker than those on the lead guitar. Likewise, thestrings on the bass (low)keys of a piano are thicker than those on the treble (high) keys.

In this lab, you will create a four-stringed musical instrument.

Materials

Four pieces of monofilament fishing string or thin wirePiece of wood (1-foot piece, 2" by 4")Eight tacksTape

Procedure

1. Use the materials available from your teacher to create a stringed musical instru-ment.

2. Your instrument must produce sounds of four pitches. The first string should have thelowest pitch. The second string should have a higher pitch; the third string, a stillhigher pitch; and the fourth string, the highest pitch.

55

/-,

GooD VmRATIONS(continued)

Conclusion

1. (a) What are some problems you encountered in construction of your instrument?

(b) How did you solve these problems?

2, Ukuleles are small, guitarlike instruments that have four strings. The first string hasthe lowest pitch and the last string the highest pitch.

(a) Which string is probably the tightest?

(b) Which string is probably the thickest?

3. What other materials might make good strings for musical instruments?

Why?

56

LESSON 6: IlEAr

6-1 DOING THE ATOMIC SHAKE

Content on Heat Energy

The Heat Is On

Matter is classified as anything that has mass and occupies space. All forms ofmatter are made up of atoms and molecules. What do you visualize when youthink of an atom or a molecule? Some people might say that they see little rounddots stacked side by side in nice ordered rows. This isn't the case. The moleculesin all forms of matter are constantly moving and jiggling about. All this shakingand moving is due to the kinetic energy these molecules possess. The amount ofkinetic energy in these molecules can be detected by the amount of heat given offby a particular form of matter. As the temperature of something increases, thekinetic energy increases.

It is easy to increase the kinetic energy in matter. Hit a baseball hard withan aluminum bat and then feel the point of impact on the bat. The bat has got-ten warmer.

SHAKE YOUR ATOMSDOWN!

;Ig'~o'/ I\\J J

57

58 6-1 Doing the Atomic Shake

This impact has caused the molecules in the metal bat to move and shakefaster. Take your hands and rub your palms together quickly. Notice that theybegin to get warm. This warmth was the result of speeding up the molecules inyour hands. As they speed up, they give off heat.

The Temperature Is Rising

Temperature is the measurement quantity that tells how warm or cold a body iswith respect to some standard. A thermometer is an instrument that measurestemperature. A thermometer contains either mercury or colored alcohol. Thesesubstances expand (rise up the thermometer) when temperature is raised andcontract (sink lower on the thermometer) when the temperature is lowered.Thermometers can be marked in the Fahrenheit scale, Celsius scale, or Kelvinscale.

On the Celsius scale (the metric scale most often used to measure temper-ature), 0 degrees represents the point at which water freezes and 100 degreesrepresents the point at which water boils. On the Fahrenheit scale, 32 degreesrepresents the freezing point and 212 degrees represents the boiling point.Kelvin is also a metric scale used to measure temperature. On this scale, tem-perature is measured in units called kelvins (K). This is a particularly usefulscale because 0 K is the lowest possible temperature that anything can reach;furthermore, 0 K is known as absolute zero and is the temperature at which allmolecular motion stops.

Temperature measures the motion of molecules or atoms in a substance.Heat is the energy that is transferred from one object to another because of tem-perature difference between objects. An increase in temperature indicates theaddition of heat. A decrease in temperature represents the removal of heat. Thecalorie is one of the units used to measure heat. One calorie is defined as theamount of heat required to raise the temperature of 1 gram of liquid water 1degree Celsius. The amount of heat needed for a given temperature changedepends on the mass of the water being heated and the specific heat of a sub-stance. Specific heat is the ability of a substance to absorb heat energy. In fact,the specific heat of a substance is the number of calories needed to raise the tem-perature of 1 gram of that substance 1 Celsius degree. Water has a specific heatrating of 1.0 calorie per gram of Celsius degree. Mercury has a specific heat of0.03, and wood has a specific heat of0.42.

Bulging Cans and Sagging Lines

As the temperature of a sub-stance is increased, its moleculesmove faster and farther apart. Theresult of this movement is expansion.Have you ever left an aluminum can ofsoda unopened in your car on a sunnyday? Chances are that the can

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6-1 Doing the Atomic Shake 59

expanded and possibly exploded by the end of the day. This is why warnings areput on aerosol spray containers not to expose them to extreme heat.

The opposite of expansion is contraction. Cold weather slows the molecularmotion of substances, and the molecules move closer together. These concepts ofexpansion and contraction must be considered when buildings are being designedand constructed. The amount of expansion of a substance depends on the amountof heat it absorbs. Why are telephone lines allowed to sag when they are strungbetween the poles in the summer? The answer lies in expansion. In the summer,when it is warm, the lines are longer; in the cold of winter, they are shorter. If thelines are strung too tightly, they might snap in the winter because they contractwhen it is cold.

How do liquids fit into the concept of expansion? Almost all liquids expandwhen they are heated. I bet you have already thought of an exception to thatstatement. Place some water in your ice trays and pop them in the freezer. Whathappens? The water freezes and expands. When heat is added, the water will con-tract. Normally this does not occur with other liquids. The odd c;rystalline struc-ture of ice explainsthe expansion of water upon freezing. .

Up, Up, and Away

What effect does temperature change have on gases? Gases expand muchmore than solids and liquids for comparable increases in temperature. But whengases are expanded they do not get warm; they get cooler. When gases are com-pressed, they do not get cool; they get warmer.

Have you ever thought about why warm air rises? When air is warmed, itexpands and becomes less dense than the surrounding air and is buoyed up likea balloon. The buoyancy is upward because the air pressure below a region ofwarmed air is greater than the pressure above. Thus the warmed air risesbecause the buoyant force is greater than its weight. If this is true, why is thetemperature not warm at high altitudes? Why are the mountain tops usually cooland covered with snow? The warm air moves from a region of greater atmosphericpressure on the ground to a region of less pressure above it. Because it is movingto a region of less pressure, the gas expands and the temperature drops.

...

'. Name Date (6-1)

IIIII

I

!i

ATOMIC SHAKE-VOCABULARY CROSSWORD PuZZLE ON

DOING THE ATOMIC SHAKE

Across

1. The quantity that tells how warm or cold a body is with respect to some standard.

7. This is the lowest possible temperature anything can reach-it is 0 degrees Kelvin.

9. The amount of heat required to raise the temperature of 1 gram of liquid 1 degreeCelsius.

10. A metal used in thermometers-responds to temperature change by contracting andexpanding.

12. This energy can be detected by the amount of heat given off by the form of matter.

16. This is the energy transferred from one object to another because of temperaturechange.

17. This is lower below a region of warmed air than above it, causing warm air to rise.

18. During this season, power lines will often sag due to expansion.

60

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9 780876 287514

VOCABULARY CROSSWORDPuZZLE(continued)

19. Metric scale used to measure temperature-absolute zero is found on this scale.

20. When gases are expanded, their temperature will becomecontracted.

than when it is

Down

2. When the temperature of substances increase, of the substance may occur.

3. The specific heat of this substance is 1.0.

4. The units used in the Kelvin scale.

5. This occurs when substances are cooled and decrease in size.

6. Metric temperature scale most often used to measure temperature (100 is boiling).

8. The ability of a substance to absorb heat energy.

11. Warm air is less than cold air, so it rises above it.

13. When gases are , they do not get cool, they get warmer.

14. The amount ofheat needed for a given temperature change depends on theof water heated.

15. These move and shake due to kinetic energy in forms of matter.

Word List

ABSOLUTE ZEROCALORIECELSIUSCOOLERCONTRACTCOMPRESSEDDENSE

EXPANSIONHEATKELVINKELVINSKINETICMASSMERCURY

MOLECULESPRESSURESPECIFIC HEATSUMMERTEMPERATUREWATER

61