chapter 12: sound...the speed ofa sound wave through a medium depends on the ... a model for...

356

You might have tried the fol-lowing experiment. With afriend, you go below the water

surface in a swimming pool andscream a message. After you come upfor air, your friend tries to guess whatwas said. Your words were hard tounderstand under water. These scubadivers use hand signals to communi-cate under water. In this chapter,learn how sound travels and hownoise differs from music. Also, learnhow musical instruments producesound, and how sound is used inmedicine.

What do you think?Science Journal Look at the picturebelow with a classmate. Discuss whatthis might be or what is happening.Here’s a hint: It’s music to your ears.Write your answer or best guess inyour Science Journal.

Sound1212

357

Think of all the different kinds of musical instru-ments you’ve seen and heard. Some have strings,

some have hollow tubes, and others have keys orpedals. Musical instruments come in many shapesand sizes and are played with various techniques. The

differences between the instruments give each one a unique sound. Whatwould an instrument made out of a ruler sound like?

Create music with a ruler1. Hold one end of a thin ruler firmly down

on a desk, allowing the free end to extend beyond the edge of the desk.

2. Gently pull up on and release the end of the ruler. What do you see and hear?

3. Vary the length of the overhanging portion and repeat the experiment several times.

ObserveHow does the length of the overhanging part of the ruler affect the sound youhear? In your Science Journal, write a paragraph about how you could writeinstructions for playing a song with the ruler.

EXPLOREACTIVITY

Making a Question Study Fold Asking yourself questions helpsyou stay focused and better understand sound when you are reading the chapter.

1. Place a sheet of paper in front of you so the short side is at the top. Fold the paper in half from the left side to the right side.

2. Fold in the top and the bottom. Unfold the paper so three equal sectionsshow.

3. Through the top thickness of paper, cut along each of the fold lines to theleft fold, forming three tabs.

4. Before you read the chapter, write these questions on the tabs: Can soundtravel through solids? Can sound travel through liquids? Can sound travelthrough gases? Now answer each question on the front of the tab.

5. As you read the chapter, write what you learn about how sound travelsunder the tabs.

FOLDABLESReading & StudySkills

FOLDABLESReading & Study Skills

Can soundtravel throughgases?

Can soundtravel through

liquids?

Can soundtravel through

solids?

358 CHAPTER 12 Sound

The Nature of SoundS E C T I O N

What causes sound? An amusement park can be a noisy place. With all the racket

of carousel music and booming loudspeakers, it can be hard tohear what your friends say. These sounds are all different, butthey do have something in common—each sound is producedby an object that vibrates. For example, your friends’ voices areproduced by the vibrations of their vocal cords, and music froma carousel and voices from a loudspeaker are produced byvibrating speakers. All sounds are created by something thatvibrates.

Sound Waves How does the sound made by a vibrating speaker get to your

ears? When an object like a radio speaker vibrates, it collideswith nearby molecules in the air, transferring some of its energyto them. These molecules then collide with other molecules inthe air and pass the energy on to them. The energy originallytransferred by the vibrating object continues to pass from onemolecule to another. This process of collisions and energytransfer forms a sound wave. Eventually, the wave reaches yourears and you hear a sound.

Sound Is a Compressional Wave Sound waves are com-pressional waves. Remember that a compressional wave is madeup of two types of regions called compressions and rarefactions.If you look at Figure 1A, you’ll see that when a radio speakervibrates outward, the nearby molecules in the air are pushed

together to form compres-sions. As Figure 1B shows,when the speaker movesinward, the nearby moleculesin the air have room to spreadout, and a rarefaction forms.As long as the speaker contin-ues to vibrate back and forth,compressions and rarefactionsare formed.

� Explain how sound travels throughdifferent mediums.

� Identify what influences thespeed of sound.

� Describe how the ear enables youto hear.

Vocabularyeardrumcochlea

The nature of sound affects how youhear and interpret sounds.

Figure 1When the speaker vibrates

outward, molecules in the airnext to it are pushed together toform a compression. Whenthe speaker vibrates inward, themolecules spread apart to form ararefaction.

Compression Rarefaction

Traveling as a Wave Compressions and rarefactions moveaway from the speaker as molecules in the air collide with theirneighbors. As the speaker continues to vibrate, more moleculesin the air are alternately pushed together and spread apart. Aseries of compressions and rarefactions forms that travels fromthe speaker to your ear. This sound wave is what you hear.

Moving Through Mediums Most sounds you hear travel through air to reach your ears.

However, if you’ve ever been swimming underwater and heardgarbled voices, you know that sound also travels through water.In fact, sound waves can travel through any type of matter—solid, liquid, or gas. The matter that a wave travels through iscalled a medium. Sound waves create compressions and rarefac-tions in any medium they travel through.

What would happen if no matter existed to form a medium?Could sound be transmitted without particles of matter to com-press, expand, and collide? On the Moon, which has no atmo-sphere, the energy in sound waves cannot be transmitted fromparticle to particle because no particles exist. Sound waves can-not travel through empty space. Astronauts must talk to eachother using electronic communication equipment.

The Speed of Sound Through Different MediumsThe speed of a sound wave through a medium depends on thesubstance the medium is made of and whether it is solid, liquid,or gas. For example, Table 1 shows that at room temperature,sound travels at 347 m/s through air, at 1,498 m/s throughwater, and at 4,877 m/s through aluminum. In general, soundtravels the slowest through gases, faster through liquids, andeven faster through solids.

What are two thingsthat affect the speedof sound?

Sound travels faster in liquids andsolids than in gases because the individ-ual molecules in a liquid or solid arecloser together than the molecules in a gas.When molecules are close together, theycan transmit energy from one to anothermore rapidly. However, the speed ofsound doesn’t depend on the loudness ofthe sound. Loud sounds travel through amedium at the same speed as soft sounds.

SECTION 1 The Nature of Sound 359

Table 1 Speed of Sound in Different Mediums

Medium Speed of Sound(in m/s)

Air 347

Cork 500

Water 1,498

Brick 3,650

Aluminum 4,877

Observing Sound inDifferent MaterialsProcedure1. Tie a piece of string onto a

metal object, such as awire hanger or a spoon, sothat you have two long endsof the string.

2. Wrap each string around afinger on each hand.

3. Gently placing your fingersin your ears, let the objectswing until it bumps againstthe edge of a chair or table.Listen to the sound.

4. Take your fingers out of yourears and listen to the soundmade by the collisions.

Analysis1. Compare and contrast the

sounds you hear when yourfingers are and are not inyour ears.

2. Do sounds travel betterthrough air or the string?

A Model for Transmitting Sound Youcan understand why solids and liquids transmitsound well by picturing a large group of peoplestanding in a line. Imagine that they are passinga bucket of water from person to person. Ifeveryone stands far apart, each person has towalk a long distance to transfer the bucket, as inFigure 2A. However, if everyone stands closetogether, as in Figure 2B, the bucket quicklymoves down the line.

The people standing close to each other arelike particles in solids and liquids. Those stand-ing far apart are like gas particles. The closer theparticles, the faster they can transfer energyfrom particle to particle.

Temperature and the Speed of SoundThe speed of sound waves also depends on thetemperature of a medium. As the temperatureof a substance increases, its molecules movefaster. This makes them more likely to collidewith each other. Remember that sound wavesdepend on the collisions of particles to transferenergy through a medium. If the particles in amedium are colliding with each other moreoften, more energy can be transferred in ashorter amount of time. Then sound wavesmove faster. For example, when the temperatureis 0°C, sound travels through the air at only 331 m/s, but at a temperature of 20°C, it speedsup to 343 m/s.

Human HearingThink of the last conversation youhad. Vocal cords and mouths movein many different ways to produce

various kinds of compressional waves, but you were somehowable to make sense of these different sound waves. Your ears andbrain work together to turn the compressional waves caused byspeech, music, and other sources into something that has mean-ing. Making sense of these waves involves four stages. First, theear gathers the compressional waves. Next, the ear amplifies thewaves. In the ear, the amplified waves are converted to nerveimpulses that travel to the brain. Finally, the brain decodes andinterprets the nerve impulses.


Figure 2A line of people passing a bucket is a model formolecules transferring the energy of a sound wave.

When the people are far away from each other,like the molecules in a gas, it takes longer to transferthe bucket of water from person to person.

The bucket travels quickly down the line whenthe people stand close together. Why would soundtravel more slowly in cork than in steel?

Outer EarGather sound waves

Middle EarAmplify waves

Hammer

Inner EarConvert waves

to nerve impulses

Anvil

Stirrup

Cochlea

EardrumEar canal

Gathering Sound Waves—The Outer Ear When youthink of your ear, you probably picture just the fleshy, visible,outer part. But, as shown in Figure 3, the human ear has threesections called the outer ear, the middle ear, and the inner ear.

The visible part of your ear, the ear canal, and the eardrummake up the outer ear. The outer ear is where sound waves aregathered. The gathering process starts with the outer part ofyour ear, which is shaped to help capture and direct soundwaves into the ear canal. The ear canal is a passageway that is 2-cm to 3-cm long and is a little narrower than your index fin-ger. The sound waves travel along this passageway, which leadsto the eardrum. The eardrum is a tough membrane about 0.1mm thick. When incoming sound waves reach the eardrum,they transfer their energy to it and it vibrates.

What makes the eardrum vibrate?

Amplifying Sound Waves—The Middle Ear When theeardrum vibrates, it passes the sound vibrations into the middleear, where three tiny bones start to vibrate. These bones arecalled the hammer, the anvil, and the stirrup. They make a leversystem that multiplies the force and pressure exerted by thesound wave. The bones amplify the sound wave. The stirrup isconnected to a membrane on a structure called the oval win-dow, which vibrates as the stirrup vibrates.

SECTION 1 The Nature of Sound 361

Figure 3The ear has three regions andeach performs specific func-tions in hearing.

Some types of hearing lossinvolve damage to theinner ear. The use of ahearing aid often canimprove hearing. Researchdifferent advertisementsfor hearing aids. Howwould you evaluate differ-ent companies’ claims thatthey are the best?

Converting Sound Waves—The Inner Ear When themembrane in the oval window vibrates, the sound vibrationsare transmitted into the inner ear. The inner ear contains thecochlea (KOH klee uh), which is a spiral-shaped structure thatis filled with liquid and contains tiny hair cells like those shownin Figure 4. When these tiny hair cells in the cochlea begin tovibrate, nerve impulses are sent through the auditory nerve tothe brain. It is the cochlea that converts sound waves to nerveimpulses.

When someone’s hearing is damaged, it’s usually because thetiny hair cells in the cochlea are damaged or destroyed, often byloud sounds. New research suggests that these hair cells may beable to repair themselves.


Section Assessment

1. Explain how sound travels from your vocalcords to your friend’s ears when you talk.

2. Compare the speed of sound wavesthrough liquids and air.

3. Explain how the temperature and densityof a medium affect the speed of soundwaves traveling through it.

4. Describe each section of the human earand its role in hearing.

5. Think Critically Some people hear ringing in their ears, called tinnitus, evenwhen there are no sound waves vibratingtheir eardrums. Form a hypothesis toexplain how this might occur.

6. Concept Mapping Prepare a concept mapthat shows the series of events that occur to produce sound. Include the terms rarefaction,medium, vibration, and compression. For morehelp, refer to the Science Skill Handbook.

7. Communicating Make a list of 10 differentsounds you’ve heard today. For each sound,identify what was vibrating to cause the sound.Write a description of the vibration and tellwhether you could see the vibration. Could you have sensed any of the sounds you heardwithout using your ears? Explain. For morehelp, refer to the Science Skill Handbook.

Figure 4These hair cells in the human earsend nerve impulses to the brainwhen sound waves cause them tovibrate. In this photo the haircells are magnified 3,900 times.

SECTION 2 Properties of Sound 363

Intensity and Loudness If the phone rings while you’re listening to the radio, you

might have to turn the radio down to be able to hear the personon the phone. What happens to the sound waves from yourradio when you adjust the volume? The notes sound the same aswhen the volume was higher, but something about the soundchanges. The difference is that quieter sound waves do not carryas much energy as louder sound waves do.

Recall that the amount of energy a wave carries correspondsto its amplitude. For a compressional wave, amplitude is relatedto the density of the particles in the compressions and rarefac-tions. Look at Figure 5. When an object vibrates strongly with alot of energy, it makes sound waves with tight, dense compres-sions. When an object vibrates with low energy, it makes soundwaves with loose, less dense compressions. The density of parti-cles in the rarefactions behaves in the opposite way. In a loudsound wave with lots of energy, the particles in its rarefactionsare far apart. In quiet sound waves with low energy, particles inthe rarefactions are closer together.

� Recognize how amplitude, inten-sity, and loudness are related.

� Describe how sound intensity ismeasured and what levels candamage hearing.

� Explain the relationship betweenfrequency and pitch.

� Discuss the Doppler effect.

Vocabularyintensity pitchloudness ultrasonicdecibel Doppler effect

The properties of sound waves determine how things sound toyou—from a blaring CD player tosomeone’s whisper.

Properties of SoundS E C T I O N



Figure 5The amplitude of a sound wavedepends on how tightly packedmolecules are in the compres-sions and rarefactions. Thissound wave has low amplitude.

This sound wave has a greateramplitude. Molecules are moretightly packed together in com-pressions and are farther apart in rarefactions.

Intensity Imagine sound waves moving through the air fromyour radio to your ear. If you held a square loop between youand the radio, as in Figure 6, and could measure how muchenergy passed through the loop in 1 s, you would measureintensity. Intensity is the amount of energy that flows through acertain area in a specific amount of time. When you turn downthe volume of your radio, you reduce the energy carried by thesound waves, so you also reduce their intensity.

Intensity influences how far away a sound can be heard. Ifyou and a friend whisper a conversation, the sound waves youcreate have low intensity and do not travel far. You have to sitclose together to hear each other. However, when you shout toeach other, you can be much farther apart. The sound wavesmade by your shouts have high intensity and can travel far.

Intensity influences how far a wave will travel because someof a wave’s energy is converted to other forms of energy when itis passed from particle to particle. Think about what happenswhen you drop a basketball. The ball has potential energy as youhold it above the ground. This potential energy is converted intoenergy of motion as the ball falls. When the ball hits the groundand bounces up, a small amount of that energy has been trans-ferred to the ground. The ball no longer has enough energy tobounce back to the original level. The ball transfers a smallamount of energy with each bounce, until finally the ball has nomore energy. If you held the ball higher above the ground, itwould have more energy and would bounce for a longer timebefore it came to a stop. In a similar way, a sound wave of lowintensity loses its energy more quickly, and travels a shorter dis-tance than a sound wave of higher intensity.


Figure 6The intensity of the sound wavesfrom the CD player is related tothe amount of energy that passesthrough the loop in a certainamount of time. How would theintensity change if the loop were 10 m away from the radio?

Whisper

Rustlingleaves

Noisyrestaurant

Chainsaw

20 25 50 75 80 100 110 120115

15

Purringcat

Averagehome

Vacuumcleaner

Jet planetaking off

Powermower

Painthreshold

0 150

Loudness in Decibels

Loudness When you hear different sounds, you do not needspecial equipment to know which sounds have greater intensity.Your ears and brain can tell the difference. Loudness is thehuman perception of sound intensity. Sound waves with highintensity carry more energy. When sound waves of high inten-sity reach your ear, they cause your eardrum to move back andforth a greater distance than sound waves of low intensity do. Thebones of the middle ear convert the increased movement of theeardrum into increased movement of the hair cells in the innerear. As a result, you hear a loud sound. As the intensity of a soundwave increases, the loudness of the sound you hear increases.

How are intensity and loudness related?

A Scale for Loudness It’s hard to say how loud too loud is.Two people are unlikely to agree on what is too loud, becausepeople vary in their perception of loudness. A sound that seemsfine to you may seem earsplitting to your teacher. Even so, theintensity of sound can be described using a measurement scale.Each unit on the scale for sound intensity is called a decibel(DES uh bel), abbreviated dB. On this scale, the faintest soundthat most people can hear is 0 dB. Sounds with intensity levelsabove 120 dB may cause pain and permanent hearing loss. Dur-ing some rock concerts, sounds reach this damaging intensitylevel. Wearing ear protection, such as earplugs, around loudsounds can help protect against hearing loss. Figure 7 showssome sounds and their intensity levels in decibels.


Research Visit the Glencoe Science Web site atscience.glencoe.com tofind a longer list of soundsand their intensities in deci-bels. Make a table that listssounds you heard today,from loudest to quietest. Inanother column, write theintensity level of each sound.

Figure 7The decibel scale measures theintensity of sound. Where woulda normal speaking voice fall on the scale?

http://www.science.glencoe.com

Pitch If you have ever taken a music class, you

are probably familiar with the musical scaledo, re, mi, fa, so, la, ti, do. If you were to singthis scale, your voice would start low andbecome higher with each note. You wouldhear a change in pitch, which is how high orlow a sound seems to be. The pitch of a soundis related to the frequency of the sound waves.

Frequency and Pitch Frequency is a measure of how manywavelengths pass a particular point each second. For a compres-sional wave, such as sound, the frequency is the number of com-pressions or the number of rarefactions that pass by eachsecond. Frequency is measured in hertz (Hz)—1 Hz means thatone wavelength passes by in 1 s.

When a sound wave with high frequency hits your ear, manycompressions hit your eardrum each second. The wave causesyour eardrum and all the other parts of your ear to vibrate morequickly than if a sound wave with a low frequency hit your ear.Your brain interprets these fast vibrations caused by high-frequency waves as a sound with a high pitch. As the frequencyof a sound wave decreases, the pitch becomes lower. Figure 8shows different notes and their frequencies. For example, awhistle with a frequency of 1,000 Hz has a high pitch, but low-pitched thunder has a frequency of less than 50 Hz.

A healthy human ear can hear sound waves with frequenciesfrom about 20 Hz to 20,000 Hz. The human ear is most sensitiveto sounds in the range of 440 Hz to about 7,000 Hz. In thisrange, most people can hear much fainter sounds than at higheror lower frequencies.

Ultrasonic and Infrasonic Waves Most people can’t hearsound frequencies above 20,000 Hz, which are called ultrasonicwaves. Dogs can hear sounds with frequencies up to about35,000 Hz, and bats can detect frequencies higher than 100,000Hz. Even though humans can’t hear ultrasonic waves, they usethem for many things. Ultrasonic waves are used in medicaldiagnosis and treatment. They also are used to estimate the size,shape, and depth of underwater objects.

Infrasonic, or subsonic, waves have frequencies below 20Hz—too low for most people to hear. These waves are producedby sources that vibrate slowly, such as wind, heavy machinery,and earthquakes. Although you can’t hear infrasonic waves, youmay feel them as a rumble inside your body.


Figure 8Every note has a different fre-quency, which gives it a distinctpitch. How does pitch changewhen frequency increases?

Making a Model for Hearing LossProcedure1. To simulate a hearing loss,

tune a radio to a news sta-tion. Turn the volume downto the lowest level you canhear and understand.

2. Turn the bass to maximumand the treble to minimum.If the radio does not havethese controls, hold thickwads of cloth over your ears.

3. Observe which sounds arehardest and easiest to hear.

Analysis1. Are high or low pitches

harder to hear? Are vowel orconsonant sounds harder tohear?

2. How could you help a personwith hearing loss understandwhat you say?

C

do

262Hz

D

re

294Hz

E

mi

330Hz

F

fa

349Hz

G

so

393Hz

A

la

440Hz

B

ti

494Hz

C

do

524Hz

Compression A

Compression A

Compression B

The Doppler Effect Imagine that you are standing at the side of a racetrack with

race cars zooming past. As they move toward you, the differentpitches of their engines become higher. As they move away fromyou, the pitches become lower. The change in pitch or wave fre-quency due to a moving wave source is called the Dopplereffect. Figure 9 shows how the Doppler effect occurs.

What is the Doppler effect?

Moving Sound As a race car moves, it sends out sound wavesin the form of compressions and rarefactions. In Figure 9A, therace car creates a compression, labeled A. Compression A movesthrough the air toward the flagger standing at the finish line. Bythe time compression B leaves the race car in Figure 9B, the carhas moved forward. Because the car has moved since the time itcreated compression A, compressions A and B are closertogether than they would be if the car had stayed still. Becausethe compressions are closer together, more compressions pass bythe flagger each second than if the car were at rest. As a result,the flagger hears a higher pitch. You also can see from Figure 9Bthat the compressions behind the moving car are farther apart,resulting in a lower frequency and a lower pitch after the carpasses and moves away from the flagger.

The car is closer to the flaggerwhen it creates compression B.Compressions A and B are closertogether in front of the car, so theflagger hears a higher-pitched sound.

Figure 9The Doppler effect occurs whenthe source of a sound wave ismoving relative to a listener.

The race car creates compression A.

The Doppler effect can alsobe observed in light wavesemanating from movingsources—although thesources must be moving attremendous speeds.Astronomers have learnedthat the universe isexpanding by observingthe Doppler effect in lightwaves. Research the phe-nomenon known as redshift and explain in yourScience Journal how itrelates to the Dopplereffect.


A Moving Observer You also can observe theDoppler effect when you are moving past a soundsource that is standing still. Suppose you were ridingin a school bus and passed a building with a ringingbell. The pitch would sound higher as youapproached the building and lower as you rodeaway from it. The Doppler effect happens any timethe source of a sound is changing position com-pared with the observer. It occurs no matterwhether it is the sound source or the observer that ismoving. The faster the change in position, thegreater the change in frequency and pitch.

Using the Doppler Effect The Doppler effect also occursfor other waves besides sound waves. For example, the frequencyof electromagnetic waves, such as radar waves, changes if anobserver and wave source are moving relative to each other.Radar guns use the Doppler effect to measure the speed of cars.The radar gun sends radar waves toward a moving car. Thewaves are reflected from the car and their frequency is shifted,depending on the speed and direction of the car. From theDoppler shift of the reflected waves, the radar gun determinesthe car’s speed. Weather radar also uses the Doppler shift toshow the movement of winds in storms, such as the tornado inFigure 10.


Section Assessment

1. When you turn up the volume on a radio,which of the following change: velocity of sound, intensity, pitch, amplitude,frequency, wavelength, or loudness?

2. What does the decibel scale measure?What decibel levels can damage hearing?

3. Compare frequency and pitch.

4. Sketch a diagram that shows why the pitchof an ambulance siren seems to change asthe ambulance passes you.

5. Think Critically Why is the Dopplereffect more dramatic when a race carspeeds past you than it is when a police car siren passes you on the street?

6. Concept Mapping Construct a network treeshowing how these concepts are related: inten-sity, loudness, decibel scale, ultrasonic, infra-sonic, pitch, and frequency. For more help,refer to the Science Skill Handbook.

7. Communicating Imagine how your life wouldbe different if you could not hear sounds at highfrequencies. Write a paragraph in your ScienceJournal discussing the sounds you would missand describing the changes you would need tomake in your life. Would there be any advan-tages? What would they be? For more help,refer to the Science Skill Handbook.

Figure 10Doppler radar can show themovement of winds in storms,and, in some cases, can detectthe wind rotation that leads tothe formation of tornadoes, likethe one shown here. This canhelp provide early warning andreduce the injuries and loss of lifecaused by tornadoes.

SECTION 3 Music 369

What is music? To someone else, your favorite music might sound like a

jumble of noise. Music and noise are caused by vibrations—with some important differences, as shown in Figure 11. Youcan easily make noise—just tap a pencil on a desk. Noise hasrandom patterns and pitches. Music is made of sounds that aredeliberately used in a regular pattern.

Natural Frequencies Every material has a particular fre-quency at which it will vibrate, called its natural frequency. Nomatter how you pluck a guitar string, you hear the same pitch,because the string always vibrates at its natural frequency. Theguitar string’s natural frequency depends on the string’s thick-ness and length and how tightly it is stretched across the guitar.Each string is tuned to a different natural frequency, which letsyou play different notes and make music. Musical instrumentscontain strings, membranes or columns of air—something thatvibrates at its natural frequency to create a pitch.

Resonance In wind instruments, the column of air insidevibrates. The air vibrates because of resonance—the ability of amedium to vibrate by absorbing energy at its own natural fre-quency. When air is blown into theinstrument, the reed or the mouth-piece vibrates. The air column absorbssome of this energy and also starts to vibrate. The resonance of the aircolumn amplifies the sound of theinstrument. Resonance helps amplifythe sound created in many musicalinstruments.

� Distinguish between noise andmusic.

� Describe why different instru-ments have different sound qualities.

� Explain how string, wind, andpercussion instruments producemusic.

� Describe the formation of beats.

Vocabularymusic overtonequality resonator

Music enhances your enjoyment oflife, but noise pollution can interferewith it.

MusicS E C T I O N

Scraping fingernails

Piano

Figure 11These wave patterns represent thesound waves created by the pianoand the scraping fingernails. Whichof these has a regularly repeatingpattern?

Sound Quality Suppose your classmate played a note on a flute and then a

note of the same pitch and loudness on a piano. Even if youclosed your eyes, you could tell the difference between the twoinstruments. Their sounds wouldn’t be the same. Each of theseinstruments has a unique sound quality. Quality of sounddescribes the differences among sounds of the same pitch andloudness. Objects can be made to vibrate at other frequenciesbesides their natural frequency. This produces sound waves withmore than one frequency. The specific combination of frequen-cies produced by a musical instrument is what gives it a distinc-tive quality of sound.

What does sound quality describe and how it iscreated?

Overtones Even though an instrument vibrates at many dif-ferent frequencies at once, you still hear just one note. All of thefrequencies are not at the same intensity. The main tone that isplayed and heard is called the fundamental frequency. On a gui-tar, for example, the fundamental frequency is produced by theentire string vibrating back and forth, as in Figure 12. In addi-tion to vibrating at the fundamental frequency, the string alsovibrates to produce overtones. An overtone is a vibration whosefrequency is a multiple of the fundamental frequency. The firsttwo guitar string overtones also are shown in Figure 12. Theseovertones create the rich sounds of a guitar. The number andintensity of overtones vary with each instrument. These over-tones produce an instrument’s distinct sound quality.

Musical Instruments A musical instrument is any device used to produce a musical

sound. Violins, cello, oboes, bassoons, horns, and kettledrumsare musical instruments that you might have seen and heard in

your school orchestra. These familiarexamples are just a small sample of thediverse assortment of instruments peo-ple play throughout the world. For exam-ple, Australian Aborigines accompanytheir songs with a woodwind instrumentcalled the didgeridoo (DIH juh ree dew).Caribbean musicians use rubber-tippedmallets to play steel drums, and a flutelikeinstrument called the nay is playedthroughout the Arab world.


Figure 12A guitar string can vibrate atmore than one frequency at thesame time. Here the guitar stringvibrations produce the funda-mental frequency, and first andsecond overtones are shown.How would the string vibrate toproduce the third overtone?

Research Visit the Glencoe Science Web site at science.glencoe.comfor information about noise pollution. Identify sources ofnoise pollution that you canhelp eliminate.

First overtone

Second overtone

Fundamental


Strings Soft violins, screaming electricguitars, and elegant harps are types of stringinstruments. In string instruments, sound isproduced by plucking, striking, or drawing abow across tightly stretched strings. Becausethe sound of a vibrating string is soft, stringinstruments usually have a resonator, like theviolin in Figure 13. A resonator (RE zen aytur) is a hollow chamber filled with air thatamplifies sound when the air inside of itvibrates. For example, if you pluck a guitarstring that is stretched tightly between twonails on a board, the sound is much quieterthan if the string were on a guitar. When thestring is attached to a guitar, the guitar frameand the air inside the instrument begin tovibrate as they absorb energy from thevibrating string. The vibration of the guitarbody and the air inside the resonator makesthe sound of the string louder and alsoaffects the quality of the sound.

Brass and Woodwinds Brass and woodwind instrumentsrely on the vibration of air to make music. The many differentbrass and wind instruments—such as horns, oboes, and flutes—use various methods to make air vibrate inside the instrument.For example, brass instruments have cone-shaped mouthpieces like the one in Figure14. This mouthpiece is inserted into metaltubing, which is the resonator in a brassinstrument. As the player blows into theinstrument, his or her lips vibrate against themouthpiece. The air in the resonator alsostarts to vibrate, producing a pitch. On theother hand, to play a flute, a musician blowsa stream of air against the edge of the flute’smouth hole. This causes the air inside theflute to vibrate.

In brass and wind instruments, thelength of the vibrating tube of air determinesthe pitch of the sound produced. For exam-ple, in flutes and trumpets, the musicianchanges the length of the resonator by open-ing and closing finger holes or valves. In atrombone, however, the tubing slides in andout to become shorter or longer.

SECTION 3 Music 371

Figure 13The air inside the violin’sresonator vibrates whenthe string is played. Thevibrating air amplifiesthe string’s sound. Whatcauses the air to vibrate?

Figure 14When the trumpetermakes the mouthpiecevibrate, the air in thetrumpet resonates toamplify the sound.

Sound waves

Percussion Does the sound of a bass drum make your heartstart to pound? Since ancient times, people have used drumsand other percussion instruments to send signals, accompanyimportant rituals, and entertain one another. Percussion instru-ments are struck, shaken, rubbed, or brushed to produce sound.Some, such as kettledrums or the drum shown in Figure 15,have a membrane stretched over a resonator. When the drum-mer strikes the membrane with sticks or hands, the membranevibrates and causes the air inside the resonator to vibrate. Theresonator amplifies the sound made when the membrane isstruck. Some drums have a fixed pitch, but others have a pitch

that can be changed by tightening or looseningthe membrane.

Caribbean steel drums were developed in the1940s in Trinidad. As many as 32 different strikingsurfaces hammered from the ends of 55-gallon oilbarrels create different pitches of sound. The sideof a drum acts as the resonator.

How have people used drums?

The xylophone shown in Figure 16 is anothertype of percussion instrument. It has a series ofwooden bars, each with its own tube-shaped res-onator. The musician strikes the bars with mallets,and the type of mallet affects the sound quality.Hard mallets make crisp sounds, while softer rub-ber mallets make duller sounds. Other types ofpercussion instruments include cymbals, rattles,and even old-fashioned washboards.

Figure 16Xylophones are made with manywooden bars that each have theirown resonator tubes. Why are theresonators and bars on a xylophonedifferent sizes?

Sound waves

Figure 15The air inside the resonator ofthe drum amplifies the soundcreated when the musicianstrikes the membrane’s surface.How does the natural frequency ofthe air in the drum affect the soundit creates?


SECTION 3 Music 373

Figure 17Beats can occur when soundwaves of different frequencies,shown in the top two panels,combine. These sound wavesinterfere with each other, form-ing a wave with a lower fre-quency, shown in the bottompanel. This wave causes a lis-tener to hear beats.

Section Assessment

1. Compare and contrast music and noise.

2. Explain how an instrument’s overtonescontribute to its sound quality.

3. Describe how a flute produces sound.

4. What happens when two instruments thatare out of pitch play the same note?

5. Think Critically The bull roarer is ablade-shaped, wooden musical instru-ment. When it is whirled around on astring, it produces a rumbling sound.Explain how this sound might be produced.

6. Recognizing Cause and Effect What causesresonance? How does resonance affect thesound quality of a musical instrument? Describehow a resonator amplifies the sound of amusical instrument. For more help, refer tothe Science Skill Handbook.

7. Communicating In your Science Journal,write a poem about music. Use the terms reso-nance, overtone, quality, and beat. For morehelp, refer to the Science Skill Handbook.

Beats Have you ever heard two flutes play the same note when they

weren’t properly tuned? The sounds they produce have slightlydifferent frequencies. You may have heard a pulsing variation inloudness called beats.

When two instruments play at the same time, the soundwaves produced by each instrument interfere. The amplitudes ofthe waves add together when compressions overlap and rarefac-tions overlap, causing an increase in loudness. When compres-sions and rarefactions overlap each other, the loudness decreases.Look at Figure 17. If two waves of different frequencies interfere,a new wave is produced that has a different frequency. The fre-quency of this wave is actually the difference in the frequencies ofthe two waves. The frequency of the beats that you hear decreasesas the two waves become closer in frequency. If two flutes that arein tune play the same note, no beats are heard.

When you are listening to music with familyor friends, describe to them what you havelearned about how musical instruments produce sound.

Making Music


3. Why were the tones different from the different test tubes? Explain.

4. Explain how resonance amplifies the soundfrom a test tube.

5. Explain how the natural frequencies of thecolumns of air in each of the tubes differ.

6. Compare and contrast the way the testtubes make music with the way a flute makes music.

There are many different types of musicalinstruments. You can also make music using

every day objects that are not formal instru-ments, such as pots and pot lids, garbage cancovers or boxes of matches. How can you create amusical instrument that requires air to be blownacross it in order to make sound?

What You’ll InvestigateHow can you make different tones using only testtubes and water?

Materialstest tubestest-tube rack

Goals� Demonstrate how to make music using

water and test tubes.� Predict how the tones will change when

there is more or less water in the test tube.

Procedure1. Put different amounts of water into each of

the test tubes.

2. Predict any differences you expect in howthe tones from the different test tubes willsound.

3. Blow across the top of each test tube.

4. Record any differences that you noticed inthe tones that you heard from each test tube .

Conclude and Apply1. Describe how the tones changed depending

on the amount of water in the test tube.

2. How did the pitch depend on the height ofthe water?

The Uses of SoundYou already know that sound, in the form of music, can pro-

vide entertainment. Sounds such as sirens and fire alarms can bewarning signals. The bell on a microwave timer tells you whenyour food is ready. People and animals use sound in a numberof important ways.

Acoustics Think of the last time you heard someone talk into a micro-

phone. Did you hear echoes? When an orchestra is done playing,does it seem as if the sound of its music lingers for a couple ofseconds? The sound waves produced by a speaker or an orchestrareflect off the walls and objects around you. The sounds andtheir reflections reach your ears at different times, so you hearechoes. This echoing effect produced by many reflections ofsound is called reverberation (rih vur buh RAY shun).

If you’re in the audience at an orchestra performance, rever-beration can ruin the sound of the music. To prevent this prob-lem, scientists and engineers who design concert halls mustunderstand how the size, shape, and furnishings of the roomaffect the reflection of sound waves. These scientists and engi-neers specialize in acoustics (uh KEW stihks), which is the studyof sound. They know, for example, that soft, porous materialscan reduce excess reverberation, so they might recommend thatthe walls of concert halls be lined with carpets and draperies.Figure 18 shows a concert hall that has been designed to create agood listening environment.

Echolocation At night, bats swoop around in darkness without

bumping into anything. They even manage to huntinsects and other prey in the dark. Their senses of sightand smell help them navigate, but many species of batsalso depend on echolocation. Echolocation is theprocess of locating objects by emitting sounds andinterpreting the sound waves that are reflected back.Look at Figure 19 to learn how echolocation works.

� Recognize some of the factors thatdetermine how a concert hall ortheater is designed.

� Describe how some animals usesound waves to hunt and navigate.

� Discuss the uses of sonar.� Explain how ultrasound is useful in

medicine.

Vocabularyacoustics sonarecholocation

Sound waves have many uses,from discovering sunken treasures to diagnosing and treating diseases.

Using SoundS E C T I O N

Figure 18This concert hall uses clothdrapes to help reduce reverbera-tions. Do you think the drapesabsorb or reflect sound waves?

375

Figure 19

VISUALIZING BAT ECHOLOCATION

Many bats emit ultrasonic—very high-frequency—sounds. The sound wavesbounce off objects, and bats locate prey

by using the returning echoes. Known as echo-location, this technique is also used by dolphins,which produce clicking sounds as they hunt. Thediagrams below show how a bat uses echolocationto capture a flying insect.

Sound waves of a bat’s ultrasonic cries spreadout in front of it.

A Some of the waves strike a moth and bounceback to the bat.

B

The bat determines the moth’s location by contin-uing to emit cries, then changes its course to catchthe moth.

C By emitting a continuous stream of ultrasoniccries, the bat homes in on the moth and captures its prey.

D


Sonar More than 140 years ago, a ship

named the Central America disappearedin a hurricane off the coast of SouthCarolina. In its hold lay 21 tons of newlyminted gold coins and bars that wouldbe worth $1 billion or more in today’smarket. When the shipwreck occurred,there was no way to search for the shipin the deep water where it sank. TheCentral America and its treasures lay atthe bottom of the ocean until 1988,when crews used sonar to locate thewreck under 2,400 m of water. Sonar isa system that uses the reflection ofunderwater sound waves to detect objects. First, a sound pulse isemitted toward the bottom of the ocean. The sound travelsthrough the water and is reflected when it hits something solid,as shown in Figure 20. A sensitive underwater microphonecalled a hydrophone picks up the reflected signal. Because thespeed of sound in water is known, the distance to the object canbe calculated by measuring how much time passes betweenemitting the sound pulse and receiving the reflected signal.

How does sonar detect underwater objects?

The idea of using sonar to detect underwater objects wasfirst suggested as a way of avoiding icebergs, but many otheruses have been developed for it. Navy ships use sonar for detect-ing, identifying, and locating submarines. Fishing crews also usesonar to find schools of fish, and scientists use it to map theocean floor. More detail can be revealed by using sound waves ofhigh frequency. As a result, most sonar systems use ultrasonicfrequencies.

Ultrasound in Medicine High-frequency sound waves are used in more than just

echolocation and sonar. Ultrasonic waves also are used to breakup and remove dirt or buildup from jewelry. Chemists some-times use ultrasonic waves to clean glassware. One of the mainuses of ultrasonic waves, though, is in medicine. Using specialinstruments, medical professionals can send ultrasonic wavesinto a specific part of a patient’s body. Reflected ultrasonicwaves are used to detect and monitor conditions such as preg-nancy, certain types of heart disease and cancer.

SECTION 4 Using Sound 377

Figure 20Sonar uses sound waves to findobjects that are underwater.How is sonar like echolocation?

Sonarsignal

Reflectedsignal

Hydrophone

Math Skills Activity

Example Problem

You send out a sonar pulse that is returned from a sunken pirate ship in 3 s. How faraway is the ship? Hint: The sonar pulse travels twice the distance from your ship to the

sunken ship.

This is what you know: speed of sound in water: v = 1,439 m/stime: t = 3 s

This is what you need to know: distance: d

This is the equation you need to use: d = vt/2

Substitute the known values: d = (1,439 m/s) (3 s) / 2 = 2,158.5 m

Check your answer by dividing the time and multiplying by 2.Do you calculate the same speed of sound that was given?

Calculating Distance with Sonar

For more help, refer to the Math Skill Handbook.

Practice Problem

The sonar pulse you emitted returns in 1 s when you are directly over thesunken treasure you were hoping to find. How far away is it?

Ultrasound Imaging Like X rays, ultrasound can beused to produce images of internal structures. A medicalultrasound technician directs the ultrasound waves towarda target area of a patient’s body. The sound waves reflect offthe targeted organs or tissues, and the reflected waves areused to produce electrical signals. A computer programconverts these electrical signals into video images, calledsonograms. Physicians trained to interpret sonograms canuse them to detect a variety of medical problems.

How does ultrasound imaging usereflected waves?

Medical professionals use ultrasound to examine many partsof the body, including the heart, liver, gallbladder, pancreas,spleen, kidneys, breast, and eye. Probably the best-known use ofultrasound in medicine is to monitor the development of a fetusin a pregnant woman’s uterus, as shown in Figure 21. Ultra-sound is better than X rays for producing images of soft tissuestructures inside the body. However, it is not as good for exam-ining bones and lungs, because hard tissues and air absorb theultrasonic waves instead of reflecting them.

Figure 21Ultrasonic waves are directedinto a pregnant woman’s uterusto form images of her fetus.What benefits can fetal sonogramsoffer expectant parents?


Treating with Ultrasound High-frequency sound wavescan be used to treat certain medical problems. For example,sometimes small, hard deposits of calcium compounds or otherminerals form in the kidneys, making kidney stones. In the past,physicians had to perform surgery to remove kidney stones. Butnow ultrasonic treatments are commonly used to break them upinstead. Bursts of ultrasound create vibrations that cause thestones to break into small pieces, as shown in Figure 22. Thesefragments then pass out of the body with the urine. A similartreatment is available for gallstones. Patients who are treatedsuccessfully with ultrasound recover more quickly than thosewho have surgery.

SECTION 4 Using Sound 379

Section Assessment

1. What are some differences between a gymand a concert hall that affect the amountof reverberation you hear in each place?

2. Explain how echolocation helps bats findfood and avoid obstacles in the dark.

3. How can sound waves be used to findobjects that are underwater?

4. Describe at least three uses of ultrasonictechnology in medicine.

5. Think Critically How is sonar technologyuseful in locating deposits of oil and min-eral resources?

6. Drawing Conclusions Imagine you are aphysician looking at an ultrasound image and an X ray of the same area of a patient’s body.A structure that you see on the X ray doesn’tappear on the ultrasound image. What can youconclude about the structure? For more help,refer to the Science Skill Handbook.

7. Solving One-Step Equations Sound travelsat about 1,500 m/s in water. How far will asonar pulse travel in 45 s? For more help,refer to the Math Skill Handbook.

Figure 22Ultrasonic waves can be used tobreak apart kidney stones.What are the benefits of ultrasoundtherapy for kidney stones?

Physicians can measureblood flow by studying theDoppler effect in ultrasonicwaves. Brainstorm howthe Doppler-shifted wavescould help doctors diag-nose diseases of the arter-ies and monitor theirhealing.

Goals� Design an experiment that tests the

effectiveness of various types of bar-riers and materials for blocking outnoise pollution.

� Test different types of materials andbarriers to determine the best noiseblockers.

Blocking Noise Pollution

380

What loud noises do you enjoy, and which ones do you find annoying? Most peo-ple enjoy a music concert performed by their favorite artist, booming displays

of fireworks on the Fourth of July, and the roar of a crowd when their team scores agoal or touchdown. Although these are loud noises, people enjoy them for short peri-ods of time. Most people find certain loud noises, such as traffic, sirens, and loudtalking, annoying. Constant, annoying noises are called noise pollution. What can bedone to reduce noise pollution? What types of barriers best block out loud noises?

Recognize the ProblemWhat types of barriers will best block out noise pollution?

Form a HypothesisBased on your experiences with loud noises, form a hypothesis about how effectivelydifferent types of barriers block out noise pollution.

Possible Materialsradio, CD player, horn, drum, or other

loud noise source shrubs, trees, concrete walls, brick walls,

stone walls, wooden fences, parked cars, or hanging laundry

sound metermeterstick or metric tape measure

Test Hypothesis

Analyze Your Data

Draw Conclusions

6. Organize the steps of your experi-ment in logical order.

Do1. Ask your teacher to examine your

plan and data table before you start.

2. Conduct your experiment asplanned.

3. Test each barrier two or three times.

4. Record your test results in your datatable in your Science Journal.

Plan1. Decide what type of barriers or

materials you will test.

2. Describe exactly how you will usethese materials.

3. Identify the controls and variablesyou will use in your experiment.

4. List the steps you will use anddescribe each step precisely.

5. Prepare a data table in your Science Journal to record yourmeasurements.

4. Compare the natural barriers youtested with the artificial barriers.Which type of barrier best reducednoise pollution?

5. Compare the different types ofmaterials the barriers were made of.Which type of material best reducednoise pollution?

1. Identify the barriers that mosteffectively reduced noise pollution.

2. Identify the barriers that leasteffectively reduced noise pollution.

3. Compare the effective barriers andidentify common characteristicsthat might explain why theyreduced noise pollution.

5. Research how noise pollution canbe unhealthy.

1. Did your results support your hypothesis?

2. Predict your results if you had useda louder source of noise such as asiren.

3. Use your results to infer how peopleliving near a busy street couldreduce noise pollution.

4. Identify major sources of noisepollution in or near your home.How could this be reduced?

ACTIVITY 381

Draw a poster illustrating how builders andlandscapers could use certain materials tobetter insulate a home or office from excessnoise pollution.

THEVOLUNOISE POLLUTION AND

HEARING LOSS

TURNING UPSCIENCEANDSociety

SCIENCE ISSUES

THAT AFFECTYOU!

382

CONNECTIONS Test Put on a blindfold and have a friend test yourhearing. Have your friend choose several noise-making objects. (Not soloud, please, and make sure you have your teacher’s permission.) Guesswhat object is making each sound.

For more information, visitscience.glencoe.com

Now hear this: More than 28 million

Americans have hearing loss. Twelve

million more people have a condition

called tinnitus (TIN uh tus), or ringing in the

ears. In at least 10 million of the 28 million

cases mentioned above, hearing loss could

have been prevented, because it was caused

by noise pollution.

People take their music very seriously in

the United States. And a lot of people like it

loud. So loud, in fact, that it can damage their

hearing. The medical term is auditory over-

stimulation. You may have experienced a

high-pitched ringing in your ears for days

after standing too close to a loudspeaker at a

concert. That’s how hearing loss starts.

Music isn’t the only cause of hearing loss

caused by noise pollution. Other kinds of

environmental noise can be strong enough to

damage the ears, too. Intense, short-duration

noise, like the sound of a gunshot or even a

thunderclap, can cause some hearing loss.

All of the structures of the inner ear can be

damaged this way. A less intense but longer

duration noise, like the sound of a lawn

mower, a low-flying plane, or a drill blasting

away at cement, can possibly damage the ear,

as well.

All the Better to Hear YouThere are 20,000 to 30,000 sensory recep-

tors, or hair cells, located in the inner ear, or

the cochlea. When vibrations reach these

hair cells, electrical impulses are triggered.

The impulses send messages to the audi-

tory center of the brain. But the human ear

was not made to withstand all the very loud

sounds of the modern world. Once hair cells

are damaged, they don’t grow back.

What can you do to avoid hearing dam-

age? Well, the first thing is to turn the volume

down on the stereo and TV. And keep the vol-

ume low when you’ve got your earphones on,

no matter how tempting it is to blast it. Also, if

you go to a rock concert, you can wear

earplugs to muffle the sound. You’ll still hear

everything, but you won’t damage your ears.

And earplugs are now small enough that

they’re pretty much undetectable. So enjoy all

that music and the street sounds of urban life,

but mind your ears.ME Did You Know?Sounds can be described by their intensity. Sounds

of high intensity carry more energy than sounds of low

intensity. Sound intensity is usually measured in units

of decibels (dB). Conversational speech is between 65

dB and 70 dB. A rock concert can measure up to 140 dB,

which is considered beyond the threshold of pain for

the ear.


384 CHAPTER STUDY GUIDE

Section 3 Music1. Music is made of sounds used deliberately

in a regular pattern.

2. Instruments use a varietyof methods to produceand amplify sound waves.How is the sound producedby vibrating strings ampli-fied by this cello?

3. When sound waves ofsimilar frequencies over-lap, they interfere witheach other to form beats.

Section 4 Using Sound1. Acoustics is the study

of sound. Why would agym be a poor place for a symphony concert?

2. Some animals emitsounds and interpretthe echoes to navigateand catch prey.

3. Sonar uses reflectedsound waves to detectobjects.

4. Ultrasound waves can be used for imagingbody tissues or treating medical conditions.

Section 1 The Nature of Sound1. Sound is a compressional wave created by

something that is vibrating.

2. Sound travels fastest through solids andslowest through gases. The speed of a soundwave also increases as the temperature ofthe medium increases. Would the sound ofthunder travel faster in a winter or summerstorm?

3. The human ear can be divided into threesections—the outer ear, the middle ear, andthe inner ear. Each section plays a specificrole in hearing.

4. Hearing involves four stages: gatheringsound waves, amplifying them, convertingthem to nerve impulses, and interpretingthe signals in the brain.

Section 2 Properties of Sound1. Intensity is a measure of how much energy

a wave carries. Humans interpret the inten-sity of sound waves as loudness.

2. The pitch of a sound becomes higher as thefrequency increases.

3. The Doppler effect is a change in frequencythat occurs when a source of sound is mov-ing relative to a listener.

Study GuideChapter 1212

Use the information onyour Question Study Foldto help explain how the

temperature of a solid, liquid, or gas affectshow sound moves.

After You ReadFOLDABLESReading & StudySkills

FOLDABLESReading & Study Skills

Guitar Flute Bongo Drum

How Played plucked blown into

Role of Resonator amplifies sound amplifies sound

Type of Instrument wind percussion

Characteristics of Musical Instruments

CHAPTER STUDY GUIDE 385

Vocabulary Wordsa. acoustics i. musicb. cochlea j. overtonec. decibel k. pitchd. Doppler effect l. qualitye. eardrum m. resonatorf. echolocation n. sonarg. intensity o. ultrasonich. loudness

Using VocabularyEach of the following sentences is false. Make

the sentence true by replacing the underlinedword with the correct vocabulary word.

1. The eardrum is filled with fluid and contains tiny hair cells that vibrate.

2. Echolocation is the study of sound.

3. A change in pitch or wave frequency due toa moving wave source is called ultrasonic.

4. Overtone is a combination of sounds andpitches that follows a specified pattern.

5. Differences among sounds of the samepitch and loudness are described as theintensity of sound.

6. Decibel is how humans perceive the intensity of sound.

Study GuideChapter 1212

Take good notes, even during lab. Lab experi-ments reinforce key concepts, and looking backat these notes can help you better understandwhat happened and why.

Study Tip

Complete the following table on musical instruments.

AssessmentChapter 1212

Choose the word or phrase that best answersthe question.

1. For a sound with a low pitch, what else isalways low? A) amplitude C) wavelengthB) frequency D) wave velocity

2. Sound intensity decreases when which ofthe following decreases?A) wave velocity C) qualityB) wavelength D) amplitude

3. When specific pitches and sounds are puttogether in a pattern, what are they called?A) overtones C) white noiseB) music D) resonance

4. Sound can travel through all but which ofthe following?A) solids C) gasesB) liquids D) empty space

5. What is the term for variations in the loudness of sound caused by wave interference?A) beats C) pitchB) standing waves D) forced vibrations

6. What does the outer ear do to sound waves?A) scatter them C) gather themB) amplify them D) convert them

7. Which of the following occurs when asound source moves away from you?A) The sound’s velocity decreases.B) The sound’s loudness increases.C) The sound’s frequency decreases.D) The sound’s frequency increases.

8. Sounds with the same pitch and loudnesstraveling in the same medium may differ inwhich of these properties?A) frequency C) qualityB) amplitude D) wavelength

9. What part of a musical instrument ampli-fies sound waves?A) resonator C) malletB) string D) finger hole

10. What is the name of the method used tofind objects that are underwater?A) sonogram C) sonarB) ultrasonic bath D) percussion

11. A car comes to a railroad crossing. Thedriver hears a train’s whistle and then hearsthe whistle’s pitch become lower. What canbe assumed about how the train is moving?

12. A whistle is blown and a dog responds, eventhough the person can’t hear the whistle.Explain.

13. Acoustic scientists sometimes do research inrooms that absorb all sound waves. Howcould such a room be used to study howbats find their food?

14. Explain why windows might begin to rattle when an airplane flies overhead.

15. The Indian sitar has extra strings that are tuned to certain pitches but are never played by the musician. Explain why these strings might be present.

16. Forming Hypotheses Sound travels slowerin air at high altitudes than at low altitudes.State a hypothesis to explain this.

17. Identifying a Question Some people saythat an ultrasound can harm a fetus. Write alist of questions to ask a doctor about thesafety of ultrasound imaging.

386 CHAPTER ASSESSMENT

CHAPTER ASSESSMENT 387

18. Making and Using Tables You use a lawnmower with a sound level of 100 dB foryour lawn-mowing business. Using thetable below, determine how many hours aday you can safely work mowing lawns.

19. Communicating Some people enjoy usingsnowmobiles. Others object to the noisethat they make. Write a proposal for a pol-icy that seems fair to both groups for theuse of snowmobiles in a state park.

20. Concept Mapping Design a concept mapthat shows how the characteristics of soundwaves are related. Include these terms: pitch,compression, medium, speed, loudness,frequency, and intensity.

21. Project Using materials you have at home,make a musical instrument. Give a demon-stration to your class. Explain how youchange the pitch of your instrument.

Lightning and thunder are alwaysassociated with each other, but they arevery different things. You see lightning,but you hear thunder. Lightning is a largedischarge of static electricity. The electri-cal energy in a lightning bolt ionizesatoms in the atmosphere and producesgreat amounts of heat. The heat causes air in the bolt’s path to expand rapidlyproducing compressional waves you hearas thunder.

Study the events listed above andanswer the following questions.

1. The different events lead to the cre-ation of thunder. Which of the follow-ing shows the correct order of events?A) D, A, C, B, E C) A, D, B, C, EB) B, A, D, C, E D) C, A, D, B, E

2. Which of the events above is mostclosely accompanied by the creation ofrarefactions?F) B H) CG) A J) E

Test Practice

AssessmentChapter 1212

Sound Level Time Permitted (dB) (hours per day)

90 8

95 4

100 2

105 1

110 0.5

Federally Recommended Noise Exposure Limits

Go to the Glencoe Science Web site at science.glencoe.com or use the Glencoe Science CD-ROM for additionalchapter assessment.

TECHNOLOGY

ARapid heating

of air

CRapid

compressionof air

EThunder

DRapid

expansionof air

BLightning


chapter 12: sound...the speed ofa sound wave through a medium depends on the ... a model for...

Documents