chapter 17 mechanical waves and sound 17.1 mechanical waves

Chapter 17 Chapter 17 Mechanical Waves and Mechanical Waves and SoundSound

17.1 Mechanical 17.1 Mechanical WavesWaves

What Are Mechanical Waves?

A A mechanical wavemechanical wave is is created when a source of created when a source of energy causes a vibration energy causes a vibration to travel through a to travel through a medium.medium.

A A mechanical wavemechanical wave is a is a disturbance in matter that disturbance in matter that carries energy from one place to carries energy from one place to another.another.

•The material through which a The material through which a wave travels is called a wave travels is called a mediummedium..

•Mechanical waves require a Mechanical waves require a medium to travel through. medium to travel through.

•A A vibrationvibration is a repeating back- is a repeating back-and-forth motion. and-forth motion.

What Are Mechanical Waves?

Types of Mechanical Waves

3 main types of mechanical waves transverse waveslongitudinal wavessurface wavesMechanical waves are classified by the way they move through a medium.

A A transverse wavetransverse wave is a wave is a wave that causes the medium to that causes the medium to vibrate at right angles to the vibrate at right angles to the direction in which the wave direction in which the wave travels.travels.

The wave carries energy The wave carries energy from left to right, in a from left to right, in a direction perpendicular to direction perpendicular to the up-and-down motion of the up-and-down motion of the rope. the rope.

Types of Mechanical Waves

Transverse WavesTransverse Waves•The highest point of the wave is The highest point of the wave is

the the crestcrest..•The lowest point of the wave is The lowest point of the wave is

the the troughtrough..

Types of Mechanical Waves

Transverse WavesTransverse Waves

Types of Mechanical Waves

CrestDirection of wave

Rest position

Direction of vibration

Trough

Longitudinal WavesLongitudinal Waves

A A longitudinal wavelongitudinal wave is a wave is a wave in which the vibration of the in which the vibration of the medium is parallel to the medium is parallel to the direction the wave travels.direction the wave travels.

Types of Mechanical Waves

Longitudinal WavesLongitudinal Waves

•An area where the particles An area where the particles in a medium are spaced close in a medium are spaced close together is called a together is called a compressioncompression. .

•An area where the particles An area where the particles in a medium are spread out is in a medium are spread out is called a called a rarefactionrarefaction..

Types of Mechanical Waves

Longitudinal WavesLongitudinal Waves

Types of Mechanical Waves

Push

Pull

Compression

Direction of wave

Rarefaction

Compression

Rest position

As compressions and As compressions and rarefactions travel along the rarefactions travel along the spring, each coil vibrates spring, each coil vibrates back and forth around its back and forth around its rest position. rest position.

Types of Mechanical Waves

Surface WavesSurface Waves

A A surface wavesurface wave is a is a wave that travels along wave that travels along a surface separating a surface separating two media.two media.

Ocean waves are the Ocean waves are the most familiar kind of most familiar kind of surface waves. surface waves.

Types of Mechanical Waves

Surface WavesSurface Waves

As the ocean As the ocean wave moves to wave moves to the right, the the right, the bobber moves in a bobber moves in a circle, returning circle, returning to its original to its original position.position.

Types of Mechanical WavesWave direction

Assessment Questions

1.1. A mechanical wave carries energy A mechanical wave carries energy from one place to another through from one place to another through the the

a.a.physical transfer of matter.physical transfer of matter.

b.b.interaction of electromagnetic interaction of electromagnetic fields.fields.

c.c. phase changes of a medium.phase changes of a medium.

d.d.vibration of a medium.vibration of a medium.

Assessment Questions

1.1. A mechanical wave carries energy A mechanical wave carries energy from one place to another through from one place to another through the the

a.a.physical transfer of matter.physical transfer of matter.

b.b.interaction of electromagnetic interaction of electromagnetic fields.fields.

c.c. phase changes of a medium.phase changes of a medium.

d.d.vibration of a medium.vibration of a medium.

Assessment Questions

2.2. In what type of wave is the In what type of wave is the vibration of the medium parallel vibration of the medium parallel to the direction in which the wave to the direction in which the wave travels?travels?a.a.transverse wavetransverse waveb.b.longitudinal wavelongitudinal wavec.c. surface wavesurface waved.d.rarefactionrarefaction

Assessment Questions

2.2. In what type of wave is the In what type of wave is the vibration of the medium parallel vibration of the medium parallel to the direction in which the wave to the direction in which the wave travels?travels?a.a.transverse wavetransverse waveb.b.longitudinal wavelongitudinal wavec.c. surface wavesurface waved.d.rarefactionrarefaction

Assessment Questions

3.3. As a surface wave travels across As a surface wave travels across water, molecules of water move in water, molecules of water move in a circular pattern. a circular pattern.

TrueTrueFalseFalse

Assessment Questions

3.3. As a surface wave travels across As a surface wave travels across water, molecules of water move in water, molecules of water move in a circular pattern. a circular pattern.

TrueTrueFalseFalse

Chapter 17: Chapter 17: Mechanical Waves Mechanical Waves and Soundand Sound

17.2 Properties of 17.2 Properties of Mechanical WavesMechanical Waves

Any motion that repeats at Any motion that repeats at regular time intervals is called regular time intervals is called periodic motionperiodic motion. .

•The time required for one The time required for one cycle is called the cycle is called the periodperiod. .

•FrequencyFrequency is the number of is the number of complete cycles in a given complete cycles in a given time.time.

•Frequency is measured in Frequency is measured in cycles per second, or cycles per second, or hertzhertz (Hz).(Hz).

Frequency and Period

A.A. A wave vibrating at one cycle per second has a frequency of 1.0 Hz.

B. A wave vibrating at two cycles per second has a frequency of 2.0 Hz.

Frequency and PeriodFrequency = 1.0 hertzOne cycle per second

Frequency = 2.0 hertzTwo cycles per second

Wavelength

Wavelength is the distance between a point on one wave and the same point on the next cycle of the wave.

Increasing the frequency of a Increasing the frequency of a wave decreases its wave decreases its wavelength.wavelength.

Transverse wavelength is measured between adjacent crests or between adjacent troughs. Longitudinal wavelength is the distance between adjacent compressions or rarefactions.

Wavelength

Wavelength can be measured from Wavelength can be measured from any point on a wave to the same any point on a wave to the same point on the next cycle of the wave. point on the next cycle of the wave.

Wavelength

Long wavelength Short wavelength

Rest position

Wave ReviewWave Review

1.1. If the horizontal distance If the horizontal distance from a crest to trough is 1.0 from a crest to trough is 1.0 m, what is the wavelength?m, what is the wavelength?

2.2. If 20 waves pass a point in 5 If 20 waves pass a point in 5 s, what is the frequency? s, what is the frequency?

Wave ReviewWave Review1.1. If the horizontal distance If the horizontal distance

from a crest to trough is 1.0 from a crest to trough is 1.0 m, what is the wavelength? m, what is the wavelength? 1.0 m1.0 m

2.2. If 20 waves pass a point in 5 If 20 waves pass a point in 5 s, what is the frequency? s, what is the frequency?

20 waves / 5 seconds = 20 waves / 5 seconds = 4 waves per second = 4Hz 4 waves per second = 4Hz

Wave Speed

How are frequency, wavelength, and speed related?

If you assume that waves If you assume that waves are traveling at a are traveling at a constant speed, then constant speed, then wavelength is inversely wavelength is inversely proportional to frequency. proportional to frequency.

When the wavelength is in meters, When the wavelength is in meters, and the frequency is in hertz, the and the frequency is in hertz, the units for speed are meters per units for speed are meters per second. second.

The speed of a wave is also The speed of a wave is also calculated by dividing its calculated by dividing its wavelength by its period. wavelength by its period.

Wave Speed

Speed of Mechanical WavesSpeed of Mechanical Waves

One end of a rope is One end of a rope is vibrated to produce a wave vibrated to produce a wave with a wavelength of 0.25 with a wavelength of 0.25 meter. The frequency of meter. The frequency of the wave is 3.0 hertz. What the wave is 3.0 hertz. What is the speed of the wave?is the speed of the wave?

Wave Speed

Speed of Mechanical WavesSpeed of Mechanical Waves

One end of a rope is vibrated to One end of a rope is vibrated to produce a wave with a produce a wave with a wavelength of 0.25 meter. The wavelength of 0.25 meter. The frequency of the wave is 3.0 frequency of the wave is 3.0 hertz. What is the speed of the hertz. What is the speed of the wave?wave?

Wave Speed

Speed = 0.25m x 3.0Hz = 0.75m/s

Wave Speed Wave Speed ExampleExample

The string of a piano that The string of a piano that produces the note middle C produces the note middle C vibrates with a frequency of vibrates with a frequency of 264 Hz. If the sound waves in 264 Hz. If the sound waves in air have a wavelength of 1.3 air have a wavelength of 1.3 m, what is the speed of sound m, what is the speed of sound in air?in air?

Wave Speed Wave Speed ExampleExample

The string of a piano that produces the The string of a piano that produces the note middle C vibrates with a note middle C vibrates with a frequency of 264 Hz. If the sound frequency of 264 Hz. If the sound waves in air have a wavelength of 1.3 waves in air have a wavelength of 1.3 m, what is the speed of sound in air?m, what is the speed of sound in air?

Speed = 1.3m x 264Hz = 363.2m/sSpeed = 1.3m x 264Hz = 363.2m/s

Wave Speed PracticeWave Speed Practice1.1. If wavelength is 15.0 m and the If wavelength is 15.0 m and the

frequency is 0.100 Hz, what is frequency is 0.100 Hz, what is the speed?the speed?

2.2. The speed of sound is 340 m/s. The speed of sound is 340 m/s. What is the wavelength of a What is the wavelength of a sound wave with a frequency of sound wave with a frequency of 220 Hz?220 Hz?

Wave Speed PracticeWave Speed Practice1.1. If wavelength is 15.0 m and the If wavelength is 15.0 m and the

frequency is 0.100 Hz, what is the frequency is 0.100 Hz, what is the speed?speed?

Speed = 15.0m x .1Hz = 1.5 m/sSpeed = 15.0m x .1Hz = 1.5 m/s2.2. The speed of sound is 340 m/s. What The speed of sound is 340 m/s. What

is the wavelength of a sound wave is the wavelength of a sound wave with a frequency of 220 Hz?with a frequency of 220 Hz?

340 m/s = m x 220Hz = 340/220 = 340 m/s = m x 220Hz = 340/220 = 1.545m1.545m

Wave speed practiceWave speed practice3. A wave has a frequency of 10 Hz 3. A wave has a frequency of 10 Hz

and a wavelength of 30 m, what and a wavelength of 30 m, what is the speed?is the speed?

4. At 254. At 25°C the speed of sound is °C the speed of sound is 346 m/s, but at 0°C it is 332 m/s. 346 m/s, but at 0°C it is 332 m/s. Why?Why?

Wave speed practiceWave speed practice3. A wave has a frequency of 10 Hz 3. A wave has a frequency of 10 Hz

and a wavelength of 30 m, what is and a wavelength of 30 m, what is the speed?the speed?

Speed = 30m x 10Hz = 300m/sSpeed = 30m x 10Hz = 300m/s4. At 254. At 25°C the speed of sound is 346 °C the speed of sound is 346

m/s, but at 0°C it is 332 m/s. Why?m/s, but at 0°C it is 332 m/s. Why?Slower moving and closer together Slower moving and closer together

molecules in the medium (air) slow molecules in the medium (air) slow the ability of the wave to movethe ability of the wave to move

Amplitude

The amplitude of a wave is the maximum displacement of the medium from its rest position.

The more energy a wave has, The more energy a wave has, the greater is its amplitude. the greater is its amplitude.

The The amplitudeamplitude of a transverse of a transverse wave is the distance from the wave is the distance from the rest position to a crest or a rest position to a crest or a trough. trough.

It takes more energy to produce It takes more energy to produce a wave with higher crests and a wave with higher crests and deeper troughs. deeper troughs.

Amplitude

The more energy a wave The more energy a wave has, the greater is its has, the greater is its amplitude.amplitude.

Amplitude

Rest position

High amplitude

Low amplitude

The The amplitudeamplitude of a of a longitudinal wave is the longitudinal wave is the maximum displacement of a maximum displacement of a point from its rest position. point from its rest position.

The more energy the wave The more energy the wave has, the more the medium has, the more the medium will be compressed or will be compressed or displaced. displaced.

Amplitude

Assessment Questions

1.1. While wading in shallow waters, While wading in shallow waters, six waves crash into your legs in a six waves crash into your legs in a 24-second span. What is the 24-second span. What is the frequency of the waves? frequency of the waves?

a.a.4 Hz4 Hz

b.b.18 Hz18 Hz

c.c. 0.25 Hz0.25 Hz

d.d.2 Hz2 Hz

Assessment Questions

1.1. While wading in shallow waters, While wading in shallow waters, six waves crash into your legs in a six waves crash into your legs in a 24-second span. What is the 24-second span. What is the frequency of the waves? frequency of the waves?

a.a.4 Hz4 Hz

b.b.18 Hz18 Hz

c.c. 0.25 Hz0.25 Hz = 6 waves / 24 = 6 waves / 24 secondsseconds

d.d.2 Hz2 Hz

Assessment Questions

2.2. What is the speed of an What is the speed of an earthquake wave if it has a earthquake wave if it has a wavelength of 2.3 km and a wavelength of 2.3 km and a frequency of 3 Hz?frequency of 3 Hz?a.a.6.9 km/s6.9 km/sb.b.5.3 km/s5.3 km/sc.c. 6.0 km/s6.0 km/sd.d.1.3 km/s1.3 km/s

Assessment Questions

2.2. What is the speed of an What is the speed of an earthquake wave if it has a earthquake wave if it has a wavelength of 2.3 km and a wavelength of 2.3 km and a frequency of 3 Hz?frequency of 3 Hz?a.a.6.9 km/s = 2.3km x 3Hz6.9 km/s = 2.3km x 3Hzb.b.5.3 km/s5.3 km/sc.c. 6.0 km/s6.0 km/sd.d.1.3 km/s1.3 km/s

Chapter 17: Chapter 17: Mechanical Waves Mechanical Waves and Soundand Sound

17.3 Behavior of 17.3 Behavior of WavesWaves

Reflection occurs when a wave bounces off a surface that it cannot pass through.

Reflection

Reflection does not change the Reflection does not change the speed or frequency of a wave, speed or frequency of a wave, but the wave can be flipped but the wave can be flipped upside down.upside down.

Refraction is the bending of a wave as it enters a new medium at an angle.

Refraction

When a wave enters a medium at an When a wave enters a medium at an angle, refraction occurs because one angle, refraction occurs because one side of the wave moves more slowly side of the wave moves more slowly than the other side.than the other side.

A lawnmower turns when it is pushed at an angle from the grass onto the gravel. The wheel on the gravel slows down, but the other wheel is still moving at a faster speed on the grass.

Refraction Grass Gravel

Left wheel is still rolling faster on grass.

Direction changes.

Mower pivots because the right wheel moves more slowly when it reaches gravel.

As an ocean As an ocean wave wave approaches approaches the shore at the shore at an angle, the an angle, the wave bends, wave bends, or refracts, or refracts, because one because one side of each side of each wave front wave front slows down slows down before the before the other side other side does. does.

Refraction

Diffraction is the bending of a wave as it moves around an obstacle or passes through a narrow opening.

Diffraction

A wave diffracts more if its A wave diffracts more if its wavelength is large compared to wavelength is large compared to the size of an opening or the size of an opening or obstacle.obstacle.

A.A. This wave diffracts, or spreads out, This wave diffracts, or spreads out, after it passes through a narrow after it passes through a narrow opening. opening.

B.B. Diffraction also occurs when a wave Diffraction also occurs when a wave encounters an obstacle. encounters an obstacle.

Diffraction

Interference occurs when two or more waves overlap and combine together.

Interference

Two types of interference are Two types of interference are constructive interferenceconstructive interference and and destructive interferencedestructive interference. .

When waves collide, they can occupy When waves collide, they can occupy the same region of space and then the same region of space and then continue on.continue on.

•Constructive interferenceConstructive interference : : when two or more waves when two or more waves combine to produce a wave combine to produce a wave with a larger displacement.with a larger displacement.

•Destructive interferenceDestructive interference : : when two or more waves when two or more waves combine to produce a wave combine to produce a wave with a smaller displacement.with a smaller displacement.

Interference

Constructive Constructive InterferenceInterference

Two waves with Two waves with equal frequencies equal frequencies travel in opposite travel in opposite directions. directions.

When a crest When a crest meets a crest, the meets a crest, the result is a wave result is a wave with an increased with an increased amplitude.amplitude.

Interference

Destructive InterferenceDestructive Interference

Two waves with Two waves with equal frequencies equal frequencies travel in opposite travel in opposite directions. directions.

When a crest When a crest meets a trough, meets a trough, the result is a the result is a wave with a wave with a reduced reduced amplitude. amplitude.

Interference

A standing wave is a wave that appears to stay in one place—it does not seem to move through the medium.

Standing Waves

A standing wave forms only if A standing wave forms only if half a wavelength or a multiple half a wavelength or a multiple of half a wavelength fits exactly of half a wavelength fits exactly into the length of a vibrating into the length of a vibrating cord.cord.

Interference occurs as the Interference occurs as the incoming waves pass incoming waves pass through the reflected through the reflected waves. waves.

At certain frequencies, At certain frequencies, interference between a interference between a wave and its reflection can wave and its reflection can produce a standing wave. produce a standing wave.

Standing Waves

A A nodenode is a point on a standing is a point on a standing wave that has no displacement wave that has no displacement from the rest position. At the from the rest position. At the nodes, there is complete nodes, there is complete destructive interferencedestructive interference between between the incoming and reflected the incoming and reflected waves. waves.

An An antinodeantinode is a point where a is a point where a crest or trough occurs midway crest or trough occurs midway between two nodes.between two nodes.

Standing Waves

These photos show These photos show standing waves for standing waves for two different two different frequencies. frequencies.

A.A. One One wavelength wavelength equals the equals the length of the length of the cord. cord.

B.B. Two Two wavelengths wavelengths equal the length equal the length of the cord.of the cord.

Standing Waves

Assessment Questions

1.1. The property of waves The property of waves bending as they pass through bending as they pass through a narrow opening is called a narrow opening is called

a.a.reflection.reflection.

b.b.refraction.refraction.

c.c.diffraction.diffraction.

d.d.destructive interference.destructive interference.

Assessment Questions

1.1. The property of waves The property of waves bending as they pass through bending as they pass through a narrow opening is called a narrow opening is called

a.a.reflection.reflection.

b.b.refraction.refraction.

c.c.diffraction.diffraction.

d.d.destructive interference.destructive interference.

Assessment Questions

2.2. When does refraction of a wave When does refraction of a wave occur? occur? a.a.The wave cannot enter the new The wave cannot enter the new

medium.medium.b.b.The wave enters a new medium The wave enters a new medium

at any angle.at any angle.c.c. The wave enters a new medium The wave enters a new medium

at any angle except 90°.at any angle except 90°.d.d.Part of the wave enters a new Part of the wave enters a new

medium and part is reflected.medium and part is reflected.

Assessment Questions

2.2. When does refraction of a wave When does refraction of a wave occur? occur? a.a.The wave cannot enter the new The wave cannot enter the new

medium.medium.b.b.The wave enters a new medium The wave enters a new medium

at any angle.at any angle.c.c. The wave enters a new medium The wave enters a new medium

at any angle except 90°.at any angle except 90°.d.d.Part of the wave enters a new Part of the wave enters a new

medium and part is reflected.medium and part is reflected.

Assessment Questions

3.3. A 6-meter rope is tied to a hook in A 6-meter rope is tied to a hook in the wall. Which of the following the wall. Which of the following wavelengths can produce a wavelengths can produce a standing wave? standing wave?

a.a.1.5 m1.5 m

b.b.2.5 m2.5 m

c.c. 3.5 m3.5 m

d.d.4.5 m4.5 m

Assessment Questions

3.3. A 6-meter rope is tied to a hook in A 6-meter rope is tied to a hook in the wall. Which of the following the wall. Which of the following wavelengths can produce a wavelengths can produce a standing wave? standing wave?

a.a.1.5 m1.5 m

b.b.2.5 m2.5 m

c.c. 3.5 m3.5 m

d.d.4.5 m4.5 m

Assessment Questions

4.4. The amount of diffraction of a The amount of diffraction of a wave increases as the size of the wave increases as the size of the obstacle causing the diffraction obstacle causing the diffraction decreases. decreases.

TrueTrueFalseFalse

Critical ThinkingCritical Thinking

If you drop a perfectly If you drop a perfectly transparent piece of glass transparent piece of glass into perfectly clear water, you into perfectly clear water, you can still see the glass. Why?can still see the glass. Why?

Chapter 17: Chapter 17: Mechanical Waves Mechanical Waves and Soundand Sound

17.4 Sound and 17.4 Sound and HearingHearing

Properties of Sound Waves

Many behaviors of sound can Many behaviors of sound can be explained using a few be explained using a few properties—speed, intensity properties—speed, intensity and loudness, and frequency and loudness, and frequency and pitch.and pitch.

Sound wavesSound waves are are longitudinal waves—longitudinal waves—compressions and compressions and rarefactions that travel rarefactions that travel through a medium. through a medium.

Properties of Sound Waves

SpeedSpeed

It takes time for sound to It takes time for sound to travel from place to place. travel from place to place.

The speed of sound varies The speed of sound varies in different media. In dry in different media. In dry air at 20°C, the speed of air at 20°C, the speed of sound is 342 meters per sound is 342 meters per second. second.

Properties of Sound Waves

Properties of Sound Waves

In general, sound waves travel In general, sound waves travel fastest in solids, slower in fastest in solids, slower in liquids, and slowest in gases.liquids, and slowest in gases.

•The speed of sound depends The speed of sound depends on many factors, including on many factors, including the density of the medium the density of the medium and how elastic the medium and how elastic the medium is.is.

Properties of Sound Waves

Intensity and LoudnessIntensity and Loudness

IntensityIntensity is the rate at which a is the rate at which a wave’s energy flows through a wave’s energy flows through a given area. given area.

•Sound intensity depends on Sound intensity depends on both the wave’s amplitude and both the wave’s amplitude and the distance from the sound the distance from the sound source.source.

•The The decibeldecibel (dB) is a unit that (dB) is a unit that compares the intensity of compares the intensity of different sounds.different sounds.

Properties of Sound Waves

Lengthy exposure to sounds Lengthy exposure to sounds more intense than 90 decibels more intense than 90 decibels can cause hearing damage. can cause hearing damage.

Properties of Sound Waves

LoudnessLoudness is a physical response is a physical response to the intensity of sound, to the intensity of sound, modified by physical factors.modified by physical factors.

•The loudness depends on The loudness depends on sound intensity. sound intensity.

•Loudness also depends on Loudness also depends on factors such as the health of factors such as the health of your ears and how your brain your ears and how your brain interprets sound waves.interprets sound waves.

Properties of Sound Waves

Frequency and PitchFrequency and Pitch

The frequency of a sound The frequency of a sound wave depends on how fast wave depends on how fast the source of the sound is the source of the sound is vibrating.vibrating.

Properties of Sound Waves

The air in the tubing of brass instruments forms a standing wave. Longer tubing makes a standing wave with a longer wavelength and a lower frequency.

The French horn can produce lower The French horn can produce lower notes than the trumpet because it can notes than the trumpet because it can make a longer tube for a standing make a longer tube for a standing wave.wave.

Properties of Sound Waves

French Horn

Trumpet

PitchPitch is the frequency of a is the frequency of a sound as you perceive it.sound as you perceive it.

•High-frequency sounds High-frequency sounds have a high pitch, and have a high pitch, and low-frequency sounds low-frequency sounds have a low pitch.have a low pitch.

Properties of Sound Waves

Ultrasound

Ultrasound is used in a Ultrasound is used in a variety of applications, variety of applications, including sonar and including sonar and ultrasound imaging.ultrasound imaging.

Most people hear sounds Most people hear sounds between 20 hertz and 20,000 between 20 hertz and 20,000 hertz.hertz.

•InfrasoundInfrasound : frequencies : frequencies lower than most people lower than most people can hear.can hear.

•UltrasoundUltrasound :frequencies :frequencies higher than most people higher than most people hearhear..

Ultrasound

SonarSonar is a technique for is a technique for determining the distance to an determining the distance to an object under water. object under water.

Ultrasound imaging is an Ultrasound imaging is an important medical technique. important medical technique. Computer software uses Computer software uses reflected pulses of ultrasound to reflected pulses of ultrasound to make a detailed map of make a detailed map of structures and organs insidestructures and organs inside the the body.body.

Ultrasound

Ultrasound can be used to make Ultrasound can be used to make images of the heart.images of the heart.

Ultrasound

The Doppler Effect

As a source of sound As a source of sound approaches, an observer approaches, an observer hears a higher frequency. hears a higher frequency. When the sound source When the sound source moves away, the observer moves away, the observer hears a lower frequency.hears a lower frequency.

The The Doppler effectDoppler effect is a is a change in sound change in sound frequency caused by frequency caused by motion of the sound motion of the sound source, motion of the source, motion of the listener, or both. listener, or both.

The Doppler Effect

Observer A hears a lower-pitch Observer A hears a lower-pitch sound than observer B because the sound than observer B because the wave fronts are farther apart for wave fronts are farther apart for observer A. observer A.

The Doppler Effect

What are the functions of the What are the functions of the three main regions of the ear?three main regions of the ear?

Hearing and the Ear

The The outer earouter ear: gathers and : gathers and focuses sound focuses sound

middle earmiddle ear: receives and : receives and amplifies the vibrationsamplifies the vibrations

inner earinner ear: uses nerve endings to : uses nerve endings to sense vibrations and send sense vibrations and send signals to the brain.signals to the brain.

Your ear Your ear consists of consists of three main three main regions—regions—the outer the outer ear, the ear, the middle ear, middle ear, and the and the inner ear. inner ear.

Hearing and the Ear Outer Ear

Middle Ear

Inner Ear

HammerAnvil

Cochlea

Auditory

Nerve

StirrupEardru

mEar

canal

How is sound recorded?How is sound recorded? How Sound Is Reproduced

Sound is recorded by Sound is recorded by converting sound waves converting sound waves into electronic signals into electronic signals that can be processed and that can be processed and stored. Sound is stored. Sound is reproduced by converting reproduced by converting electronic signals back electronic signals back into sound waves.into sound waves.

How do musical How do musical instruments vary pitch?instruments vary pitch?

Music

Most musical instruments Most musical instruments vary pitch by changing the vary pitch by changing the frequency of standing waves.frequency of standing waves.

Resonance is the response of a Resonance is the response of a standing wave to another wave standing wave to another wave of the same frequency. Musical of the same frequency. Musical instruments often use instruments often use resonance to amplify sound.resonance to amplify sound.

•One wave can “push” One wave can “push” another wave to a higher another wave to a higher amplitude.amplitude.

•Resonance can produce a Resonance can produce a dramatic increase in dramatic increase in amplitude. amplitude.

Music

Sound-absorbing Sound-absorbing tiles in this tiles in this auditorium reduce auditorium reduce unwanted unwanted reflections. The reflections. The curved reflecting curved reflecting panels above the panels above the stage help gather stage help gather and direct sound and direct sound waves toward the waves toward the audience.audience.

Music

Sound QuestionSound Question

The speed of sound in The speed of sound in ocean water is 1530 m/s. If ocean water is 1530 m/s. If it takes 3 s for a sound it takes 3 s for a sound wave to make a round trip wave to make a round trip from a sonar device, what is from a sonar device, what is the distance to the the distance to the reflecting object?reflecting object?

Assessment Questions

1.1. The intensity of sound waves is The intensity of sound waves is measured in units of measured in units of

a.a.hertz (Hz).hertz (Hz).

b.b.decibels (dB).decibels (dB).

c.c. joules (J).joules (J).

d.d.meters (m).meters (m).

Assessment Questions

2.2. Most musical instruments vary Most musical instruments vary pitch by pitch by a.a.changing the amplitude of sound changing the amplitude of sound

waves.waves.b.b.reflecting sound from surfaces in reflecting sound from surfaces in

a room.a room.c.c. changing the frequency of a changing the frequency of a

standing wave.standing wave.d.d.using the Doppler effect.using the Doppler effect.

Assessment Questions3.3. The Doppler effect is The Doppler effect is

a.a. a change in sound frequency caused a change in sound frequency caused by motion of the sound source by motion of the sound source relative to the listener.relative to the listener.

b.b. used in a variety of applications used in a variety of applications including sonar and ultrasound including sonar and ultrasound imaging.imaging.

c.c. a technique for determining the a technique for determining the distance to an object under water.distance to an object under water.

d.d. the rate at which a wave’s energy the rate at which a wave’s energy flows through a given area.flows through a given area.