Chapter 21 sound
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Chapter 21: Sound. Pages 532 - 557. Sound is a form of energy produced by the vibration of matter. Sound is a compressional or longitudinal wave Ex. Spring Sound is transmitted through solids, liquids, and gases. Sound is transmitted better through solids and liquids. Why? More dense

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Chapter 21: Sound

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Chapter 21 sound

Chapter 21: Sound

Pages 532 - 557


Chapter 21 sound

  • Sound is a form of energy produced by the vibration of matter.

  • Sound is a compressional or longitudinal wave

    • Ex. Spring

  • Sound is transmitted through solids, liquids, and gases.


Chapter 21 sound

  • Sound is transmitted better through solids and liquids. Why?

    • More dense

  • Gases transmits sound a lot farther than a solid and liquid. Why?

    • Less dense; not as many particles to interfere.


Sound

Sound

  • So what causes sounds to travel better through some substances and not others?

    • The greater the elasticity, the greater the speed.

    • The greater the density, the slower the speed.

    • The best conductors of sound are elastic substances.


Chapter 21 sound

  • Sound can not be transmitted through a vacuum.

    • Sound needs a medium in order for it to be transmitted.

  • Radio waves can travel through a vacuum; no medium is needed.

    • This is why astronauts can use radio signals to talk in space.


Speed of sound

Speed of Sound

  • 344 m/s in air at 20°C

  • Depends on:

    • Type of medium

      • travels better through liquids and solids

      • can’t travel through a vacuum

    • Temperature of medium

      • travels faster at higher temps


Parts of the ear

Parts of the ear

  • Outer ear: pinna

  • Ear canal

  • Ear drum: tympanum

    • Vibrates the ear drum


Chapter 21 sound

  • Middle ear: three small bones

    • Anvil

    • Hammer

    • Stirrup

  • Inner ear

    • Cochlea: filled with fluid

      • Hair-like nerve endings

      • Auditory nerves


Brain

Brain

  • Damage done to the hairs causes permanent hearing loss. The hairs never grow back.


B human hearing

B. Human Hearing

sound wave

vibrates ear drum

amplified by bones

converted to nerve impulses in cochlea


Human hearing

Human Hearing

  • Pitch

    • highness or lowness of a sound

    • depends on frequency of sound wave

    • human range: 20 - 20,000 Hz

ultrasonic waves

subsonic waves


Frequencies you cannot hear

Ultrasonic: higher than 20,000 Hz

Uses: clean jewelry, medical applications

Infrasonic: lower than 20 Hz

Found: in the atmosphere and in the crust when plates move; also an indication motion sickness

Frequencies you cannot hear


Human hearing1

Human Hearing

  • Intensity

    • volume of sound

    • depends on energy (amplitude) of sound wave

    • measured in decibels (dB)


Sound is measured in what

Sound is measured in what?

  • Above 120 dB can cause hearing loss.


Human hearing2

Human Hearing

DECIBEL SCALE

120

110

100

80

70

40

18

10

0


Doppler effect

Doppler Effect

  • Doppler Effect

    • change in wave frequency caused by a moving wave source

  • moving toward you - pitch sounds higher

  • moving away from you - pitch sounds lower


Reflection of sound waves

Reflection of Sound Waves

  • Echoes

  • Echolocation: process using reflected sound waves to find objects

    • Bats

    • Whales

    • SONAR

    • Ultrasonography


Seeing with sound

Medical Imaging

SONAR

“Sound Navigation and Ranging”

Seeing with Sound

  • Ultrasonic waves - above 20,000 Hz


Diffraction

Diffraction

  • Bends of waves around or through a barrier

    Examples:

  • Thunder

  • Someone in the hallway on the other side and we

    can hear them.


D interference

Constructive - louder

Destructive - softer

D. Interference

  • Interference

    • the ability of 2 or more waves to combine to form a new wave


D interference1

D. Interference

  • Beats

    • variations in sound intensity produced by 2 slightly different frequencies

    • both constructive and destructive interference occur


Interference

Interference

  • The effects caused by 2 or more waves.

    • Ex. Several instruments produce interference in a band.


Cool interference examples

Cool Interference Examples:

  • The Sound Barrier: the point at which the source of a sound accelerates to the speed of sound

  • Sonic Booms: the explosive sound heard when a shock wave reaches your ears

  • 1st time sound barrier broken: Oct. 14, 1947 by Chuck Yeager (speed of sound is called Mach 1); so Mach 6 is going 6 times the speed of sound


Sound barrier and sonic booms

Sound Barrier and Sonic Booms


Movie clip of breaking the sound barrier

Movie Clip of Breaking the sound barrier


Resonance

Resonance

  • Forced Vibration

    • when one vibrating object forces another object to vibrate at the same frequency

    • results in a louder sound because a greater surface area is vibrating

    • used in guitars, pianos, etc.


Resonance1

Resonance

  • Resonance

    • special case of forced vibration

    • object is induced to vibrate at its natural frequency


Harmonics

Harmonics

  • Fundamental

    • the lowest natural frequency of an object

  • Overtones

    • multiples of the fundamental frequency


Chapter 21 sound

  • Examples

    • Fundamental – 100 Hz

    • 1st Overtone – 200 Hz

    • 2nd Overtone – 300 Hz


Music vs noise

Music vs. Noise

  • Music

    • specific pitches and sound quality

    • regular pattern

  • Noise

    • no definite pitch

    • no set pattern


Interference1

Interference

  • Beats

    • variations in sound intensity produced by 2 slightly different frequencies

    • both constructive and destructive interference occur


Acoustics

Anechoic chamber - designed to eliminate reverberation.

Acoustics

  • Acoustics

    • the study of sound

  • Reverberation

    • echo effect produced by the reflection of sound


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