chapter 11: sound - core 8-2 sciencebkscience.weebly.com/uploads/1/6/3/2/16325492/chap11.pdf ·...

320320

Cracking the Sound BarrierHave you ever heard the crack of a sonicboom? A sonic boom occurs when a planeexceeds the speed of sound. Sound wavescreate a cone-shaped shock wave comingfrom the aircraft. Behind the cone are low-pressure regions that can cause water vaporto condense, forming the cloud you see here.

Write three things that you wouldlike to learn about sound.Science Journal

sections

1 The Nature of Sound

2 Properties of Sound

3 MusicLab Making Music

4 Using SoundLab Blocking Noise Pollution

Virtual Lab How is an oscilloscopeused to tune a musical instrument?

Sound

321321

Sound Make the followingFoldable to help identify whatyou already know, what you

want to know, and what you learned aboutsound.

Fold a verticalsheet of paper fromside to side. Makethe front edgeabout 1.25 cmshorter than the back edge.

Turn lengthwiseand fold intothirds.

Unfold and cut only the top layeralong both folds to make three tabs.

Label each tab as shown.

Identify Questions As you read the chapter, writewhat you learn about sound traveling throughsolids under the left tab of your Foldable, what youlearn about sound traveling through liquids underthe center tab, and what you learn about soundtraveling through gases under the right tab.

STEP 4

STEP 3

STEP 2

STEP 1

What sound does a ruler make?Think of the musical instruments you’ve seenand heard. Some have strings, some havehollow tubes, and others have keys or pedals.Musical instruments come in many shapesand sizes and are played with various tech-niques. These differences give each instru-ment a unique sound. What would aninstrument made from a ruler sound like?

1. Hold one end of a thin ruler firmly downon a desk, allowing the free end to extendbeyond the edge of the desk.

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

3. Vary the length of the overhanging por-tion and repeat the experiment severaltimes.

4. Think Critically In your Science Journal,write instructions for playing a song withthe ruler. Explain how the length of theoverhanging part of the ruler affects thesound.

Start-Up Activities

Can soundtravel through

liquids?


solids?


gases?

Preview this chapter’s contentand activities atgpscience.com

http://gpscience.com

322 CHAPTER 11 Sound

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 produced byan object that vibrates. For example, your friends’ voices are pro-duced by the vibrations of their vocal cords, and music from acarousel and voices from a loudspeaker are produced by vibrat-ing speakers. All sounds are created by something that vibrates.

Sound Waves When an object like a radio speaker vibrates, it collides with

nearby molecules in the air, transferring some of its energy tothem. These molecules then collide with other molecules in theair and pass the energy on to them. The energy originally trans-ferred by the vibrating object continues to pass from one mole-cule to another. This process of collisions and energy transferforms a sound wave.

Sound waves are compressional waves. Remember that acompressional wave is made up of two types of regions calledcompressions and rarefactions. If you look at Figure 1, you’ll seethat when a radio speaker vibrates outward, the nearby mole-cules in the air are pushed together to form compressions. As thefigure shows, when the speaker moves inward, the nearby mole-cules in the air have room to spread out, and a rarefactionforms. As long as the speaker continues to vibrate back andforth, compressions and rarefactions are formed.

The Nature of SoundReading Guide

■ Explain how sound travelsthrough different mediums.

■ Identify what influences thespeed of sound.

■ Describe how the ear enablesyou to hear.

The nature of sound affects howyou hear and interpret sounds.

Review Vocabularyvibration: rhythmic back-and-forthmotion

New Vocabulary

• eardrum

• cochlea

Compression

Rarefaction

When the speaker vibrates inward,the molecules spread apart to forma rarefaction.

When the speaker vibrates out-ward, molecules in the air next to it are pushed together to form a compression.

Figure 1 The vibration of aspeaker produces compressionalwaves.

SECTION 1 The Nature of Sound 323

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.

The Speed Of SoundMost 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 in Different Materials The speedof a sound wave through a medium depends on the substancethe medium is made of and whether it is solid, liquid, or gas. Forexample, Table 1 shows that at room temperature, sound travelsat 347 m/s through air, at 1,498 m/s through water, and at4,877 m/s through aluminum. In general, sound travels theslowest through gases, faster through liq-uids, and even faster through solids.

What are two thingsthat affect the speedof sound?

Sound travels faster in liquids andsolids than in gases because the individualmolecules in a liquid or solid are closertogether 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.

Listening to SoundThrough DifferentMaterialsProcedure1. Tie the middle of a length of

string onto a metal object,such as a wire hanger or aspoon, so that the string hastwo long ends.

2. Wrap each string endaround a finger on each hand.

3. Gently placing your fingersin your ears, swing theobject 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 whenyour fingers are and arenot in your ears.

2. Do sounds travel betterthrough air or the string?

Table 1 Speed of Soundin Different Mediums

Medium Speed of Sound (in m/s)

Air 347

Cork 500

Water 1,498

Brick 3,650

Aluminum 4,877

A Model for Transmitting Sound You canunderstand why solids and liquids transmitsound well by picturing a large group of peo-ple standing in a line. Imagine that they arepassing a bucket of water from person to per-son. If everyone stands far apart, each personhas to walk a long distance to transfer thebucket, as in the top photo of Figure 2.However, if everyone stands close together, asin the bottom photo of Figure 2, the bucketquickly moves 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 tempera-ture is 0°C, sound travels through the air atonly 331 m/s, but at a temperature of 20°C, itspeeds up to 343 m/s.

Human HearingThink of the last conversation you had.Vocal cords and mouths move in many

different ways to produce various kinds of compressional waves,but you were somehow able to make sense of these differentsound waves. Your ears and brain work together to turn thecompressional waves caused by speech, music, and other sourcesinto something that has meaning. Making sense of these wavesinvolves four stages. First, the ear gathers the compressionalwaves. Next, the ear amplifies the waves. In the ear, the amplifiedwaves are converted to nerve impulses that travel to the brain.Finally, the brain decodes and interprets the nerve impulses.


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

When the people are far away from each other, like themolecules in a gas, it takes longer to transfer the bucketof water from person to person.

The bucket travels quickly down the line when the peo-ple stand close together. Explain why sound would travel more slowly in corkthan in steel.

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 sound wavesinto 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 about0.1 mm 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.

Figure 3 The ear has threeregions that perform specificfunctions in hearing.

Audiology Some types ofhearing loss involve dam-age to the inner ear. Theuse of a hearing aid oftencan improve hearing.Audiologists diagnoseand treat people withhearing loss. Researchthe field of audiology.Find out what educationis required for people togain certification as audi-ologists, and the settingsin which they work.

Outer EarGathers sound waves

Middle EarAmplifies waves

Hammer

Inner EarConverts waves

to nerve impulses

Anvil

Stirrup

Cochlea

EardrumEar canal

SECTION 1 The Nature of Sound 325


Self Check1. Explain how sound travels from your vocal cords to

your friend’s ears when you talk.

2. Summarize the physical reasons that sound wavestravel at different speeds through liquids and gases.

3. Explain why sound speeds up when the temperaturerises.

4. Describe in detail each section of the human ear and itsrole in hearing.

5. Think Critically Some people hear ringing in their ears,called tinnitus, even in the absence of sound. Form ahypothesis to explain why this occurs.

Summary

Sound Waves and Their Causes

• Sound results from compressional wavesemanating from vibrating objects.

• The compressions and rarefactions of soundwaves transfer energy.

Moving Through Materials

• Sound waves can travel through any matter.

• Sound travels fastest through solids, slowerthrough liquids, and slowest through gases.

• Sound travels faster in warmer mediums.

Human Hearing

• The outer ear gathers sound waves anddirects them to the eardrum.

• The middle ear contains three tiny bones thatmultiply the force and pressure of the vibrat-ing eardrum.

• The inner ear’s cochlea converts sound wavesto nerve impulses.

6. Calculate Time How long would it take a sound wavefrom a car alarm to travel 1 km if the temperaturewere 0°C?

7. Calculate Time How long would it take the same wave to travel 1 km if the temperature were 20°C?

gpscience.com/self_check_quiz

Converting Sound Waves—The Inner Ear When themembrane in the oval window vibrates, the sound vibrations aretransmitted 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.

Figure 4 These hair cells in thehuman ear send nerve impulses tothe brain when sound waves causethem to vibrate. In this photo thehair cells are magnified 3,900 times.

http://gpscience.com/self_check_quiz

SECTION 2 Properties of Sound 327

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

might have to turn down the volume on the stereo to be able tohear the person on the phone. What happens to the sound wavesfrom your radio when you adjust the volume? The notes soundthe same as when the volume was higher, but something aboutthe sound changes. The difference is that quieter sound wavesdo not carry as 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. For a sound wave that carries less energyand has a lower amplitude, particles in the medium are lesscompressed in the compressions and lessspread out in the rarefactions. For asound wave that has a higher amplitude,particles in the medium are closertogether, or more compressed, in thecompressions and more spread out in therarefactions.

To produce a wave that carries moreenergy, more energy is transferred fromthe vibrating object to the medium. Moreenergy is transferred to the mediumwhen the particles of the medium areforced closer together in the compres-sions and spread farther apart in the rar-efractions.

Properties of SoundReading Guide

■ 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.

Each property of a sound waveaffects how things sound to you—from your blaring CD player tosomeone’s whisper.

Review Vocabularypotential energy: energy that isstored in an object’s position

New Vocabulary

• intensity • pitch

• loudness • ultrasonic

• decibel • Doppler effect

Compression Rarefaction

Compression Rarefaction

Low-amplitude sound wave

High-amplitude sound wave

Figure 5 The amplitude of asound wave depends on howtightly packed molecules are in thecompressions and rarefactions.


Intensity Imagine sound waves moving through the airfrom your radio to your ear. If you held a square loop betweenyou and the radio, as in Figure 6, and could measure how muchenergy passed through the loop in 1 s, you would measure inten-sity. Intensity is the amount of energy that flows through a cer-tain area in a specific amount of time. When you turn down thevolume 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 Decreases With Distance Intensity influenceshow far a wave will travel because some of a wave’s energy is con-verted to other forms of energy when it is passed from particle toparticle. Think about what happens when you drop a basketball.The ball has potential energy as you hold it above the ground. Thispotential energy is converted into energy of motion as the ball falls.When the ball hits the ground and bounces up, a small amount ofthat energy has been transferred to the ground. The ball no longerhas enough energy to bounce back to the original level. The balltransfers a small amount of energy with each bounce, until finallythe ball has no more energy. If you held the ball higher above theground, it would have more energy and would bounce for a longertime before it came to a stop. In a similar way, a sound wave of lowintensity loses its energy more quickly, and travels a shorter distancethan a sound wave of higher intensity.

Figure 6 The intensity of thesound waves from the CD player isrelated to the amount of energythat passes through the loop in acertain amount of time.Describe how the intensitywould change if the loop were 10 m away from the radio.

Michael Newman/PhotoEdit, Inc.


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 intensityreach your ear, they cause your eardrum to move back and fortha 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?

The Decibel Scale It’s hard to say how loud too loud is. Twopeople are unlikely to agree on what is too loud, because peo-ple 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(DE suh 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.During some rock concerts, sounds reach this damaging inten-sity level. Wearing ear protection, such as earplugs, around loudsounds can help protect against hearing loss. Figure 7 showssome sounds and their intensity levels in decibels.

Figure 7 The decibel scalemeasures the intensity of sound. Identify where a normal speakingvoice would fall on the scale.

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

Topic: Sound Intensity Visit gpscience.com for Web linksto information about sound aswell as a list of sounds and theirintensities in decibels.

Activity Make a table that listssome sounds you heard today, inorder from loudest to quietest. Inanother column, write the intensitylevel of each sound.

(l to r)Mark A. Schneider/Visuals Unlimited, Ian O'Leary/Stone/Getty Images, Rafael Macia/Photo Researchers, David Young-Wolff/PhotoEdit, Inc., SuperStock



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 would heara change in pitch, which is how high or low asound seems to be. The pitch of a sound isrelated 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 sensi-tive to 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 8 Every note has a differ-ent frequency, which gives it adistinct pitch. Describe how pitch changes whenfrequency increases.

C

do

262Hz

D

re

294Hz

E

mi

330Hz

F

fa

349Hz

G

so

393Hz

A

la

440Hz

B

ti

494Hz

C

do

524Hz

Simulating HearingLossProcedure1. Tune a radio to a news

station. Turn the volumedown to the lowest levelyou can hear and under-stand.

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

3. Observe which sounds arehardest and easiest to hear.

Analysis1. Are high or low pitches

harder to hear? Are vowelor consonant soundsharder to hear?

2. How could you help aperson with hearingloss understandwhat you say?

Compression A

Compression B

Compression A


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 Doppler effect.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 closer togetherthan they would be if the car had stayed still. Because the com-pressions are closer together, more compressions pass by the flag-ger each second than if the car were at rest. As a result, the flaggerhears a higher pitch. You also can see from Figure 9B that thecompressions behind the moving car are farther apart, resultingin a lower frequency and a lower pitch after the car passes andmoves away from the flagger.

Figure 9 The Doppler effect occurs whenthe source of a sound wave is moving relativeto a listener.

The race car creates compression A.

The car is closer to the flagger when itcreates compression B. Compressions A and Bare closer together in front of the car, so theflagger hears a higher-pitched sound.

Red Shift The Dopplereffect can also be observedin light waves emanatingfrom moving sources—although the sources mustbe moving at tremendousspeeds. Astronomers havelearned that the universeis expanding by observingthe Doppler effect inlight waves. Researchthe phenomenon knownas red shift and explainin your Science Journalhow it relates to theDoppler effect.


Self Check1. Determine which will change if you turn up a radio’s

volume: wave velocity, intensity, pitch, amplitude,frequency, wavelength, or loudness.

2. Describe the range of human hearing in decibels, andthe level at which sound can damage human ears.

3. Contrast frequency and pitch.

4. Draw and label a diagram that explains the Dopplereffect.

5. Think Critically Why would a passing race car displaymore Doppler effect than a passing police siren?

SummaryIntensity and Loudness

• Tight, dense compressions in a sound wavemean high intensity, loudness, and moreenergy.

• Sound intensity is measured in decibels.

Pitch

• High frequency sound waves have closer com-pressions and rarefactions and higher pitchthan those of low frequency.

• Ultrasonic waves are too high for people tohear, but are useful for medical purposes.

The Doppler Effect

• The Doppler effect occurs when a movingobject emits sounds that change pitch as theobject moves past you.

• Police radar uses the Doppler effect to detectspeeding cars.

6. Make a Table Using the musical scale in Figure 8,make a table that shows how many wavelengths willpass you in 1 min for each musical note. What is therelationship between frequency and the number of wavelengths that pass you in 1 min?

A Moving Observer You also can observe the Doppler effectwhen you are moving past a sound source that is standing still.Suppose you were riding in a school bus and passed a buildingwith a ringing bell. The pitch would sound higher as youapproached the building and lower as you rode away from it.The Doppler effect happens any time the source of a sound ischanging position compared with the observer. It occurs nomatter whether it is the sound source or the observer that ismoving. The faster the change in position, the greater thechange 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.

Figure 10 Doppler radar canshow the movement of winds instorms, and, in some cases, candetect the wind rotation that leadsto the formation of tornadoes, likethe one shown here. This can helpprovide early warning and reducethe injuries and loss of life causedby tornadoes.

gpscience.com/self_check_quizNOAA/OAR/ERL/National Severe Storms Laboratory (NSSL)


SECTION 3 Music 333

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. Noisehas random patterns and pitches. Music is made of sounds thatare deliberately used in a regular pattern.

Natural Frequencies Every material or object has a particularset of frequencies at which it vibrates. This set of frequencies are itsnatural frequencies. When you pluck a guitar string the pitch youhear depends on the string’s natural frequencies. Each stringon a guitar has a different set of natural frequencies. The nat-ural frequencies of a guitar string depend on the string’sthickness, its length, the material it is made from, and howtightly it is stretched. Musical instruments containstrings, membranes, or columns of air that vibrate attheir natural frequencies to produce notes with differ-ent pitches.

Resonance The sound produced by musical instru-ments is amplified by resonance. Recall that resonanceoccurs when a material or an object is made to vibrate atits natural frequencies by absorbing energy from some-thing that is also vibrating at those frequencies. The vibra-tions of the mouthpiece or the reed in a wind instrumentcause the air inside the instrument to absorb energy andvibrate at its natural frequencies. The vibrating air makesthe sound of the instrument louder.

Music

Figure 11 These wave patternsrepresent the sound waves createdby the piano and the scrapingfingernails. Determine which of these has aregularly repeating pattern.

Reading Guide

■ Distinguish between noise andmusic.

■ Describe why different instrumentshave different sound qualities.

■ Explain how string, wind, andpercussion instruments producemusic.

■ Describe the formation of beats.

Music makes life more enjoyable,but noise pollution is unpleasant.

Review Vocabularyfrequency: the number of vibrationsoccurring in 1 s

New Vocabulary

• music

• sound quality

• overtone

• resonator

Scraping fingernails

Piano

(t)Jean Miele/The Stock Market/CORBIS, (b)Mark Burnett


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. Sound qualitydescribes 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 isit created?

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 kettledrums aremusical instruments that you might have seen and heard in yourschool orchestra. These familiar examples are just a small sample

of the diverse assortment of instrumentspeople play throughout the world. Forexample, 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 12 A guitar string canvibrate at more than one fre-quency at the same time. Here theguitar string vibrations producethe fundamental frequency, andfirst and second overtones areshown. Infer how the string would vibrateto produce the third overtone.

Topic: Noise Pollution Visit gpscience.com for Web linksto information about noisepollution.

Activity Identify sources of noisepollution that you can help elimi-nate. Write your findings in yourScience Journal.

First overtone

Second overtone

Fundamental


SECTION 3 Music 335

Strings Soft violins, screaming electric gui-tars, and elegant harps are types of stringinstruments. In string instruments, sound isproduced by plucking, striking, or drawing abow across tightly stretched strings. Because thesound of a vibrating string is soft, string instru-ments usually have a resonator, like the violin inFigure 13. A resonator (RE zuh nay tur) is ahollow chamber filled with air that amplifiessound when the air inside of it vibrates. Forexample, if you pluck a guitar string that isstretched tightly between two nails on a board,the sound is much quieter than if the stringwere on a guitar. When the string is attached toa guitar, the guitar frame and the air inside theinstrument begin to vibrate as they absorbenergy from the vibrating string. The vibrationof the guitar body and the air inside the res-onator makes the sound of the string louderand also affects 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. Forexample, brass instruments have cone-shaped mouthpieces likethe one in Figure 14. This mouthpiece isinserted into metal tubing, which is the res-onator in a brass instrument. As the playerblows into the instrument, his or her lipsvibrate against the mouthpiece. The air in theresonator also starts to vibrate, producing apitch. On the other hand, to play a flute, amusician blows a stream of air against the edgeof the flute’s mouth hole. This causes the airinside the flute to vibrate.

In brass and wind instruments, the lengthof the vibrating tube of air determines thepitch of the sound produced. For example, influtes and trumpets, the musician changesthe length of the resonator by opening andclosing finger holes or valves. In a trombone,however, the tubing slides in and out tobecome shorter or longer.

Sound waves

Figure 14 Whenthe trumpeter makesthe mouthpiece vibrate,the air in the trumpetresonates to amplifythe sound.

Figure 13 The air insidethe violin’s resonatorvibrates when the stringis played. The vibratingair amplifies the string’ssound. Explain what causes theair to vibrate.

(t)Charles Gupton/Stone/Getty Images, (b)Will Hart/PhotoEdit, Inc.

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 pitchthat can be changed by tightening or loosening the 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 side ofa 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 of per-cussion instruments include cymbals, rattles, andeven old-fashioned washboards.

Figure 15 The air inside the res-onator of the drum amplifies thesound created when the musicianstrikes the membrane’s surface. Describe how the natural fre-quency of the air in the drumaffects the sound it creates.

Figure 16 Xylophones are madewith many wooden bars that eachhave their own resonator tubes. Explain why the resonators andbars on a xylophone are differentsizes.

Sound waves

(t)N

ick

Row

e/P

hoto

Dis

c, (

b)D

eric

k A

. Tho

mas

, D

at's

Jaz

z/C

OR

BIS

SECTION 3 Music 337

Self Check1. Compare and contrast music and noise.

2. Explain how an instrument’s overtones contribute to itssound quality.

3. Explain how a flute, violin, and kettledrum producesound.

4. Describe what occurs when two out-of-tune instru-ments play the same note.

5. Think Critically Why do musical instruments vary indifferent regions of the world?

SummaryNature of Music

• Music is sound used in regular patterns.

• Every material has a set of natural frequenciesat which it will vibrate.

• Resonance helps amplify the sound producedby musical instruments.

Sound Quality

• Quality of sound describes the differencesamong sounds of the same pitch and loudness.

• Sound quality results from specific combina-tions of frequencies produced in variousmusical instruments.

Beats

• The interference of two waves with differentfrequencies produces beats.

6. Calculate Frequencies A string on a guitar vibrateswith a frequency of 440 Hz. Two beats are heard whenthis string and a string on another guitar are played atthe same time. What are the possible frequencies of vibration of the second string?

Beats Have you ever heard two

flutes play the same note whenthey weren’t properly tuned?The sounds they produce haveslightly different frequencies.You may have heard a pulsingvariation in loudness, calledbeats.

When two instruments playat 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.

How are beats produced?

Figure 17 Beats can occur whensound waves of different frequen-cies, shown in the top two panels,combine. These sound waves inter-fere with each other, forming awave with a lower frequency,shown in the bottom panel. Thiswave causes a listener to hearbeats.



There are many different types of musicalinstruments. Early instruments were madefrom materials that were easily obtainedsuch as clay, shells, skins, wood, and reeds.These materials were fashioned into variousinstruments that produced pleasing sounds.In this lab, you are going to create a musicalinstrument using materials that are availableto you—just as your ancestors did.

Real-World QuestionHow can you make different tones using onlytest tubes and water?

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 a test tube.

Materialstest tubestest-tube rack

Safety Precautions

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 noticein the tones that you hear from eachtest tube.

Conclude and Apply1. Describe how the tones change depending

on the amount of water in the test tube.

2. Explain why the pitch depends on theheight of the water.

3. Summarize why each test tube produces adifferent tone.

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

5. Explain how the natural frequencies of theair columns in each of the tubes differ.

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

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


Making Mu� ic

Doug Martin

SECTION 4 Using Sound 339

AcousticsWhen an orchestra stops playing, does it seem as if the sound

of its music lingers for a couple of seconds? 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).

During an orchestra performance, reverberation can ruinthe sound of the music. To prevent this problem, scientists andengineers who design concert halls must understand how thesize, shape, and furnishings of the room affect the reflection ofsound waves. These scientists and engineers specialize inacoustics (uh KEW stihks), which is the study of sound. Theyknow that soft, porous materials can reduce excess reverbera-tion, so they might recommend that the walls of concert halls belined with carpets and draperies. Figure 18 shows a concert hallthat has been designed to create a good listening environment.

EcholocationAt night, bats swoop around in darkness without bumping

into anything. They even manage to find insects and other prey inthe dark. Their senses of sight and smell help them navigate. Manyspecies of bats also depend on echolocation. Echolocation is theprocess of locating objects by emitting sounds and interpreting thesound waves that are reflected back. Look at Figure 19 to learn howecholocation works.

Using SoundReading Guide

■ Recognize some of the factorsthat determine how a concerthall or theater is designed.

■ Describe how some animalsuse sound waves to hunt andnavigate.

■ Discuss the uses of sonar.■ Explain how ultrasound is useful

in medicine.

Sound waves have many uses, fromdiscovering sunken treasures todiagnosing and treating diseases.

Review Vocabularyecho: the reflection of a soundfrom a surface

New Vocabulary

• acoustics

• echolocation

• sonar

Figure 18 This concert halluses cloth drapes to help reducereverberations.Explain how the drapes absorb orreflect sound waves.

Araldo de Luca/CORBIS

Figure 19

VISUALIZING BAT ECHOLOCATION


Many bats emit ultrasonic—very high-fre-quency—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 from a bat’s ultrasonic criesspread out 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 capturesits prey.

D

(tr)Merlin D. Tuttle, (bl)Gary W. Carter/CORBIS


SonarMore 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 MedicineHigh-frequency sound waves are used in more than just

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

Figure 20 Sonar uses soundwaves to find objects that areunderwater.Describe how sonar is likeecholocation.

Sonarsignal

Reflectedsignal

Hydrophone


Ultrasound Imaging Like X rays, ultrasound can be used toproduce images of internal structures. A medical ultrasoundtechnician directs the ultrasound waves toward a target area ofa patient’s body. The sound waves reflect off the targetedorgans or tissues, and the reflected waves are used to produceelectrical signals. A computer program converts these electri-cal signals into video images, called sonograms. Physicianstrained to interpret sonograms can use them to detect a vari-ety of medical problems.

How does ultrasound imaging use reflected waves?

Medical professionals use ultrasound to examine many partsof the body, including the heart, liver, gallbladder, pancreas,spleen, kidneys, breast, and eye. Ultrasound also is used to mon-itor the development of a fetus, as shown in Figure 21. However,ultrasound does not produce good images of the bones andlungs, because hard tissues and air absorb the ultrasonic wavesinstead of reflecting them.

Figure 21 Ultrasonic waves aredirected into a pregnant woman’suterus to form images of her fetus.

USING SONAR A sonar pulse returns in 3 s from a sunken ship directly below. Find the depth

of the ship if the speed of the pulse is 1,439 m/s. Hint: the sonar pulse travels a distance

equal to twice the depth of the ship, so use the equation d = st/2 to find the depth.

known values and the unknown value

Identify the known values:

speed of sound in water v � 1,439 m/s

time for round trip t � 3 s

Identify the unknown value:

The depth of the ship d � ? m

the problem

Substitute the known values, t � 3 s and s = 1,439 m/s, into the equation for the depth:

d � �s2t� ��

(1,439 m2

/s)(3 s)��

12

� 4,317 m � 2,158.5 m

your answer

Divide the distance by the time and multiply by 2. You should get the same speed of sound.

CHECK

SOLVE

means

means

means

IDENTIFY

Solve a Simple Equation

Find the speed of a sonar pulse that returns in 2.0 s from a sunken ship at 1,500 m depth.

For more practice problems go to page 834, and visit gpscience.com/extra_problems.

Doug Martin

http://gpscience.com/extra_problems


Self Check1. Describe some differences between a gym and a concert

hall that might affect the amount of reverberation in each.

2. Explain how echolocation helps bats to find food andavoid obstacles.

3. Explain how sound waves can be used to find underwaterobjects.

4. Describe at least three uses of ultrasonic technology inmedicine.

5. Think Critically How is sonar technology useful inlocating deposits of oil and minerals?

6. Calculate Distance Sound travels at about 1,500 m/sin seawater. How far will a sonar pulse travel in 45 s?

7. Calculate Time How long will it take for an underseasonar pulse to travel 3 km?

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 must have surgery.

Figure 22 Ultrasonic waves canbe used to break up kidney stones.Explain why ultrasound therapy isbeneficial for treating kidney stones.


Doppler Waves Physicianscan measure blood flowby studying the Dopplereffect in ultrasonic waves.Brainstorm how theDoppler-shifted wavescould help doctors diagnosediseases of the arteries andmonitor their healing.

SummaryAcoustics

• Acoustics is a field in which scientists andengineers work to control the quality of soundin spaces.

Echolocation

• Bats locate objects by emitting sounds andthen interpreting their reflected sound waves.

Sonar

• Humans using sonar can interpret reflectedsound to locate objects underwater.

Ultrasound in Medicine

• High-frequency sound waves are useful fordetecting and monitoring certain medicalconditions.

• Medical ultrasound is also used to cure prob-lems like kidney stones and gallstones.


Design Your OwnDesign Your Own

Real-World QuestionWhat loud noises do you enjoy, and which ones do you find annoying?Most people enjoy a music concert performed by their favorite artist,booming displays of fireworks on the Fourth of July, and the roar of acrowd when their team scores a goal or touchdown. Although theseare loud noises, most people enjoy them for short periods of time.Most people find certain loud noises, such as traffic, sirens, and loudtalking, annoying. Constant, annoying noises are called noise pollu-tion. What can be done to reduce noise pollution? What types ofbarriers best block out loud noises? What types of barriers will bestblock out noise pollution?

Form a HypothesisBased on your experiences with loud noises, form a hypothesis thatpredicts the effectiveness of different types of barriers at blocking outnoise pollution.

Test HypothesisMake a Plan1. Decide what type of barriers or materials you will test.

2. Describe exactly how you will use these materials.

Goals■ Design an experiment

that tests the effective-ness of various types ofbarriers and materialsfor blocking out noisepollution.

■ Test different types ofmaterials and barriersto determine the bestnoise blockers.

Possible Materialsradio, CD player, horn,

drum, or other loudnoise source

shrubs, trees, concretewalls, brick walls, stonewalls, wooden fences,parked cars, or hanginglaundry

sound metermeterstick or metric tape

measure

Blocking NfisePollution

344

John

Wan

g/P

hoto

Dis

c

3. Identify the controls and variables you will use in yourexperiment.

4. List the steps you will use and describe each step precisely.

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

6. Organize the steps of your experiment in logical order.

Follow Your Plan1. Ask your teacher to approve your plan and data table before

you start.

2. Conduct your experiment as planned.

3. Test each barrier two or three times.

4. Record your test results in your data table in your ScienceJournal.

Analyze Your Data 11. Identify the barriers that most effectively reduced noise pollution.

2. Identify the barriers that least effectively reduced noise pollution.

3. Compare the effective barriers and identify common characteristics that mightexplain why they reduced noise pollution.

4. Compare the natural barriers you tested with the artificial barriers. Which typeof barrier best reduced noise pollution?

5. Compare the different types of materials the barriers were made of. Whichtype of material best reduced noise pollution?

Conclude and Apply1. Evaluate whether your results support your hypothesis.

2. Predict how your results would differ if you use a louder source of noise suchas a siren.

3. Infer from your results how people living near a busy street could reduce noise pollution.

4. Identify major sources of noise pollution in ornear your home. How could this be reduced?

5. Research how noise pollution can beunhealthy.

LAB 345

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

David Young-Wolff/PhotoEdit, Inc.

Now hear this: More than 28 millionAmericans have hearing loss. Twelvemillion more people have a condition

called tinnitus (TIN uh tus), or ringing in theears. In at least 10 million of the 28 millioncases mentioned above, hearing loss couldhave been prevented, because it was caused bynoise pollution.

People take their music very seriously in theUnited States. And a lot of people like it loud. Soloud, in fact, that it can damage their hearing.The medical term is auditory overstimulation.You may have experienced a high-pitched ring-ing in your ears for days after standing too closeto a loudspeaker at a concert. That’s how hearingloss starts.

Music isn’t the only cause of hearing losscaused by noise pollution. Other kinds of environ-mental noise can be strong enough to damage theears, too. Intense, short-duration noise, like thesound of a gunshot or even a thunderclap, can

cause some hearing loss. Allof the structures

of the innerear can bedamagedthis way.

A less intense but longer durationnoise, like the sound of a lawn mower, alow-flying plane, or a drill blasting awayat 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 thecochlea. When vibrations reach these hair cells,electrical impulses are triggered.

The impulses send messages to the auditorycenter of the brain. But the human ear was notmade to withstand all the very loud sounds ofthe modern world. Once hair cells are damaged,they don’t grow back.

What can you do to avoid hearing damage?Well, the first thing is to turn the volume downon the stereo and TV. And keep the volume lowwhen you’ve got your earphones on, no matterhow tempting it is to blast it. Also, if you go to arock concert, you can wear earplugs to mufflethe sound. You’ll still hear everything, but youwon’t damage your ears. And earplugs are nowsmall enough that they’re pretty much unde-tectable. So enjoy all that music and the streetsounds of urban life, but mind your ears.

SCIENCEANDSocietySCIENCE ISSUES

THAT AFFECTYOU!

Noise Pollutionand Hearing Loss

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

For more information, visitgpscience.com/time

(tl)Australian Picture Library/CORBIS, (tr)Zig Leszczynski/Earth Scenes, (bl)David Sacks

http://gpscience.com/time

The Nature of Sound

1. Sound is a compressional wave created bysomething that is vibrating.

2. Sound travels fastest through solids andslowest through gases. You see the flash oflightning before you hear the clap of thunderbecause light travels faster than sound.

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.

Properties of Sound

1. Intensity is a measure of how much energya 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.

Music

1. Music is made ofsounds used deliber-ately in a regularpattern.

2. Instruments, suchas this flute, use avariety of methodsto produce andamplify sound waves.

3. When sound wavesof similar frequenciesoverlap, they interferewith each other toform beats.

Using Sound

1. Acoustics is thestudy of sound.This gym is greatfor playing basket-ball, but the soundquality would bepoor for a concert.

2. Sonar usesreflected soundwaves to detectobjects.

3. Ultrasound wavescan be used for imaging body tissues ortreating medical conditions.

CHAPTER STUDY GUIDE 347gpscience.com/interactive_tutor

Use the Foldable that you made at the begin-ning of this chapter to help you review sound.

(tl)Planet Earth Pictures/FPG/Getty Images, (tr)CMCD/PhotoDisc, (br)Robert Brenner/PhotoEdit, Inc.

http://gpscience.com/interactive_tutor

Fill in the blanks with the correct vocabularyword or words.

1. The _________ is filled with fluid and con-tains tiny hair cells that vibrate.

2. _________ is the study of sound.

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

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

5. Differences among sounds of the samepitch and loudness are described as_________.

6. _________ is how humans perceive theintensity of sound.

7. _________ is a scale for sound intensity.

Choose the word or phrase that best answers thequestion.

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

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

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

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

12. What is the term for variations inthe loudness of sound caused by waveinterference?A) beatsB) standing wavesC) pitchD) forced vibrations

13. What does the outer ear do to soundwaves?A) scatter them C) gather themB) amplify them D) convert them

14. 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.

15. Sounds with the same pitch and loudnesstraveling in the same medium may differin which of these properties?A) frequency C) qualityB) amplitude D) wavelength

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

17. What is the name of the method used tofind objects that are underwater?A) sonogramB) ultrasonic bathC) sonarD) percussion

348 CHAPTER REVIEW

acoustics p. 339cochlea p. 326decibel p. 329Doppler effect p. 331eardrum p. 325echolocation p. 339intensity p. 328loudness p. 329

music p. 333overtone p. 334pitch p. 330resonator p. 335sonar p. 341sound quality p. 334ultrasonic p. 330

gpscience.com/vocabulary_puzzlemaker

http://gpscience.com/vocabulary_puzzlemaker

CHAPTER REVIEW 349gpscience.com/chapter_review

18. Copy and complete the following table onmusical instruments.

Use the table below to answer question 19.

19. You use a lawn mower with a sound levelof 100 dB. Using the table above, deter-mine the maximum number of hours aweek you can safely work mowing lawnswithout ear protection.

20. Infer A car comes to a railroad crossing.The driver hears a train’s whistle and itspitch becomes lower. What can beassumed about how the train is moving?

21. Form Hypotheses Sound travels slower in airat high altitudes than at low altitudes.Form a hypothesis to explain this.

22. Apply Acoustic scientists sometimes doresearch in rooms that absorb all soundwaves. How could such a room be used tostudy how bats find their food?

23. Explain why windows might begin to rattlewhen an airplane flies overhead.

24. Communicate Some people enjoy usingsnowmobiles. Others object to the noisethat they make. Write a proposal for apolicy that seems fair to both groups forthe use of snowmobiles in a state park.

Use the wave speed equation v = f λ to answerquestions 25–27.

25. Calculate Frequency A sonar pulse has awavelength of 3.0 cm. If the pulse has aspeed in water of 1,500 m/s, calculateits frequency.

26. Calculate Wavelength What is the wave-length of a sound wave with a frequencyof 440 Hz if the speed of sound in air is340 m/s?

27. Calculate Wave Speed An earthquake pro-duces a seismic wave that has a wave-length of 650 m and a frequency of10 Hz. How fast does the wave travel?

28. Calculate Distance The sound of thundertravels at a speed of 340 m/s andreaches you in 2.6 s. How far away isthe storm?

29. Calculate Time The shipwrecked CentralAmerica was discovered lying beneath2,400 m of water. If the speed of soundin seawater is 1,500 m/s, how long willit take a sonar pulse to travel to theshipwreck and return?

Characteristics of Musical Instruments

Guitar Flute Bongo Drum

How Played plucked blown into

Role of Resonator amplifies amplifies sound sound

Type of Instrument wind percussion

Federally Recommended NoiseExposure Limits

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

90 8

95 4

100 2

105 1

110 0.5

http://gpscience.com/chapter_review

Record your answers on the answer sheetprovided by your teacher or on a sheet of paper.

1. What does a sound’s frequency determine?A. pitch C. intensityB. amplitude D. energy

2. Which medium does sound travel fastestthrough?A. empty space C. gasesB. liquids D. solids

Use the table below to answer questions 3 and 4.

3. Which of the following would sound theloudest?A. vacuum cleanerB. chain sawC. power mowerD. purring cat

4. Which of the following statements is trueabout a sound of 65 decibels?A. It causes intense pain.B. It can cause permanent hearing loss.C. It cannot be heard by anyone.D. It can be heard without discomfort or

damage.

5. To which group of instruments does aclarinet belong?A. electronic C. stringedB. percussion D. wind

6. Which of the following will lower the pitchof the sound made by a guitar string?A. shortening the vibrating stringB. tightening the stringC. plucking the string harderD. loosening the string

Use the illustration below to answer questions 7 and 8.

7. If the fundamental frequency of a guitarstring is 262 Hz, what is the frequency ofthe first overtone?A. 262 Hz C. 786 HzB. 524 Hz D. 1048 Hz

8. What is the frequency of the secondovertone if the fundamental frequencyis 294 Hz?A. 294 Hz C. 882 HzB. 588 Hz D. 1176 Hz

9. If you were on a moving train, whatwould happen to the pitch of the bell at acrossing as you approached and thenpassed by the crossing?A. pitch would increase and then decreaseB. pitch would remain the sameC. pitch would decrease and then increaseD. pitch would keep decreasing

10. On what does a guitar string’s naturalfrequency depend?A. thickness C. lengthB. tightness D. all of these

350 STANDARDIZED TEST PRACTICE

First overtone

Second overtone

Fundamental

Sound Loudness (dB)

Jet taking off 150

Pain threshold 120

Chain saw 115

Power mower 110

Vacuum cleaner 75

Average home 50

Purring cat 25

STANDARDIZED TEST PRACTICE 351

Record your answers on the answer sheetprovided by your teacher or on a sheet of paper.

Use the table below to answer questions 11–13.

11. A “fishfinder” sends out a pulse of ultra-sound and measures the time needed forthe sound to travel to a school of fish andback to the boat. If the fish are 16 m belowthe surface, how long would it take soundto make the round trip in the water?

12. Suppose you are sitting in the bleachers ata baseball game 150 m from home plate.How long after the batter hits the ball doyou hear the “crack” of the ball and bat?

13. Suppose a friend is 500 m away along arailroad track while you have your ear tothe track. He drops a stone on the tracks.How long will the sound take to reachyour ear?

14. Explain why placing your hand on a bellthat has just been rung will stop the soundimmediately.

15. Why do different musical instrumentshave different sound qualities?

Record your answers on a sheet of paper.

16. Explain why people who work on theground near jet runways wear big earmuffs filled with a sound insulator.

Use the illustration below to answer questions 17 and 18.

17. Describe the path of sound from the timeit enters the ear until a message reachesthe brain.

18. Would sound waves traveling through theouter ear travel faster or slower that thosetraveling through the inner ear? Explain.

19. Science-fiction movies often show battlesin space where an enemy spaceshipexplodes with a very loud sound. Explainwhether or not this scenario is accurate.

20. Compare the way a violin, a flute, anddrum produce sound waves. What acts asa resonator in each instrument?

21. How can interference produce a sound withdecreased loudness? How can interferenceproduce a sound with increased loudness?

22. Imagine you have been hired by a schoolto reduce the amount of reverberationthat occurs in the classrooms. Whatrecommendations would you make?

gpscience.com/standardized_test

Medium Speed of Sound (m/s)

Air 347

Water 1,498

Iron 5,103

Outer Ear

Middle Ear Inner Ear

Make Sure the Units Match Read carefully and make note ofthe units used in any measurement.

Question 11 Compare the units given in the table with those inthe problem. If the units do not match, you will have to do unitconversions.

http://gpscience.com/standardized_test

chapter 11: sound - core 8-2 sciencebkscience.weebly.com/uploads/1/6/3/2/16325492/chap11.pdf ·...

Documents