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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

Chapter 21: Sound

Pages 532 - 557

slide2
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.
slide3
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.
slide5
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
slide8
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
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
slide29
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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