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Sound

Chapter 16

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Nature of Sound

Sound is a disturbance that travels through a medium as a longitudinal wave.

Sound is a mechanical wave because it requires a medium

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Speed of Sound

The speed of sound is 346 m/s at room temperature.

The speed of sound depends on elasticity, density, and temperature of the medium.

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Speed of Sound

Elasticity is the ability of a material to bounce back after being disturbed.

Density is the amount of matter in a given volume.

Temperature is a measure of the average kinetic energy.

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Speed of Sound

Sound travels more quickly in mediums that have a high degree of elasticity.

Sound travels more slowly in denser materials.

Sound travels more slowly at a lower temperature and faster at higher temperature.

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Energy is required to create a sound wave. Sound energy is also known as . . .

A. B. C. D.

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A. Elastic potential energy

B. Radiant energy

C. Acoustic energy

D. Thermal energy

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Properties of Sound

Intensity of a sound wave is the amount of energy that a wave carries per second through a unit area.

Loudness describes what you actually hear.

A sound wave of greater intensity generally sound louder.

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Sound Loudness

The loudness of sound is measured in decibels.

Threshold of hearing is at 0 decibels.

Sound louder than 120 decibels can cause pain and permanent damage.

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Frequency & Pitch

Frequency is the number of sound waves that pass a given point in a given amount of time.

Human hearing is between 20 Hz and 20,000 Hz.

Ultrasound is sound waves above the normal human hearing range.

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Frequency & Pitch

Infrasound are sound waves that are below the normal range of human hearing.

Pitch of a sound is a description of how high or low the sound seems to a person.

Pitch of a sound that you hear depends on the frequency of the sound wave.

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As the frequency of a sound wave increases . . . .

A. B. C. D.

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A. Pitch increases.

B. Pitch decreases.

C. Pitch stays the same.

D. HELP! I don’t get it!

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Resonance

Resonance occurs when the frequency of the sound waves and the natural frequency of the objects are the same.

If resonance occurs in an object that is not flexible, the object will break (shattering of a glass).

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The Doppler Effect

The apparent change in frequency as a wave source moves in relation to the listener is called the Doppler Effect.

As sound source moves toward the listener, the waves reach the listener with a higher frequency.

The pitch appears to increase because of the Doppler effect.

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Combining Sound Waves

Timbre describes the quality of the sound you hear.

The blending of the fundamental tone and the overtones makes up the characteristic sound quality, or timbre, of a particular sound.

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Music

Music is a set of tones combined in ways that are pleasing to the ear.

Types of instruments:– Strings– Brass– Woodwinds– Percussion

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Noise

Noise has no pleasing timbre and no identifiable pitch.

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Interference of Sound Waves

Interference occurs when two or more sound waves interact.

Acoustics describe how well sound can be heard in a particular room or hall.

Repeated change in loudness are called beats.

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Hearing Sound

The outer ear funnels sound waves, the middle ear transmits the waves inward, and the inner ear converts the sound waves into a form that your brain can understand.

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Outer Ear

The outer ear funnels the sound waves to the ear canal.

The sound travels down the ear canal and vibrates the eardrum.

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Middle Ear

The middle ear contains three small bones: hammer, anvil and stirrup.

The vibrations travel from the eardrum to the hammer, then the anvil and finally the stirrup.

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Inner Ear

The stirrup vibrates the cochlea.

The cochlea contains fluid and tiny hairs that are stimulated by the vibrations.

The stimulations of the tiny hairs send messages to the brain.

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Hearing Loss

Hearing loss is caused by:

– Injury– Infection– Aging (like me?)

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Facts:

More than 40 million Americans have hearing loss. Approximately 40% of the hearing-impaired are

under age 65. About 2 million children under age 18 are hearing-

impaired in the U.S. Minor decreases in hearing, especially of higher

frequencies, are normal after age 20. Some form of hearing loss affects 1 out of 5 people

by age 55.

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Facts:

One-third of Americans between the ages of 65 and 74 - and one-half of those age 85 and older - have some form of hearing loss.

Hearing loss is the third leading chronic disability, following arthritis and high blood pressure.

Between 7 and 10 million people in American industry have noise-induced hearing loss, virtually all of which was preventable.

About 15% of college graduates have a level of hearing loss equal to or greater than their parents; a significant cause is listening to loud music.

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Facts:

In the U.S., 12 million people have hearing aids. Of the 12 million with hearing aids, only 6 million

actually wear them eight hours a day, seven days a week.

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Application of Sound

An echo is a reflected sound wave.

Some surfaces absorb sound waves.

Other surfaces reflect sound waves

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Sonar

Sonar is a system of detecting reflected sound waves.

Sonar stands for sound navigation and ranging.

A sonar device measures the time it takes to detect the reflected sound waves.

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Ultrasound

Ultrasonic frequency is sound waves above 20,000 Hz.

Echolocation is the use of sound waves to determine distance or to locate objects.

Bats use echolocation to navigate and to find food.

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Ultrasound (continue)

Ultrasound produce pictures called sonogram.

Doctors use ultrasound to look inside the human body and to diagnose and treat medical conditions.

Ultrasound is used for focusing cameras, brushing teeth and cleaning jewelry.

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Test

This Tuesday/Wednesday, March 3rd/4th. Covers all of sound waves in chapter 16.

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Review Questions

What type of wave is sound? (longitudinal) What are three factors that affect the speed of

sound? (elasticity, density & temperature) What are the three bones in the middle ear? (hammer, anvil & stirrup) Is sound faster in warmer or cooler temperatures? (warmer)

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Review Questions

Is sound faster in elastic material or material that is not elastic?

(elastic) Is sound faster in less dense or more dense

medium? (less dense) What does the stirrup shake in the middle ear? (cochlea) What does sonar stand for? (sound navigating and ranging)

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Review Questions

How do bats navigate? (echolocation) What effect describes an increasing pitch as a loud noise

is approaching and decreasing pitch as a loud noise is moving away?

(Doppler Effect) What is the property of sound that is described as the

amount of energy that passes by a point each second? (intensity) How loud or soft noise is appears to be is known as

___________. (pitch)

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Review Questions

What you hear is known as _______________. (loudness) Sound is measured in ________________. (decibels) Sound waves with frequencies below the human

range of hearing is known as _______________. (infrasound) Sound waves with frequencies above the human

range of hearing is known as _______________. (ultrasound)

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Review Questions

When the frequency of an object and the natural frequency are the same, it is known as _______________.

(resonance) _______________ describes the quality of sound. (timbre) What group of instrument vibrates the lips to produce sound? (brass) What group of instruments vibrates a reed to produce sound? (wood-wind)

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Review Questions

What group of instruments produces sound by rubbing, plucking or striking a string?

(string) What group of instruments produces sound by being struck? (percussions) Sound with no identifiable pitch and unpleasing to the ear is

known as _______________. (noise) Sound pleasing to the ear with an identifiable pitch is known as

_______________. (music)

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Review Questions

_______________ describes how well sound can be heard in a particular room.

(acoustics).