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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

Chapter 21 sound

Chapter 21 sound

Sound matter.

  • 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. matter.

    • 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 matter.

  • 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 matter.

  • Outer ear: pinna

  • Ear canal

  • Ear drum: tympanum

    • Vibrates the ear drum

Chapter 21 sound

Brain matter.

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

B human hearing
B. Human Hearing matter.

sound wave

vibrates ear drum

amplified by bones

converted to nerve impulses in cochlea

Human hearing
Human Hearing matter.

  • 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 matter.

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 matter.

  • 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? matter.

  • Above 120 dB can cause hearing loss.

Human hearing2
Human Hearing matter.











Doppler effect
Doppler Effect matter.

  • 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 matter.

  • Echoes

  • Echolocation: process using reflected sound waves to find objects

    • Bats

    • Whales

    • SONAR

    • Ultrasonography

Seeing with sound

Medical Imaging matter.


“Sound Navigation and Ranging”

Seeing with Sound

  • Ultrasonic waves - above 20,000 Hz

Diffraction matter.

  • Bends of waves around or through a barrier


  • Thunder

  • Someone in the hallway on the other side and we

    can hear them.

D interference

Constructive matter. - louder

Destructive - softer

D. Interference

  • Interference

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

D interference1
D. Interference matter.

  • Beats

    • variations in sound intensity produced by 2 slightly different frequencies

    • both constructive and destructive interference occur

Interference matter.

  • The effects caused by 2 or more waves.

    • Ex. Several instruments produce interference in a band.

Cool interference examples
Cool Interference Examples: matter.

  • 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 matter.

  • 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.

Resonance matter.

  • Resonance

    • special case of forced vibration

    • object is induced to vibrate at its natural frequency

Harmonics matter.

  • Fundamental

    • the lowest natural frequency of an object

  • Overtones

    • multiples of the fundamental frequency

Chapter 21 sound

  • Examples matter.

    • Fundamental – 100 Hz

    • 1st Overtone – 200 Hz

    • 2nd Overtone – 300 Hz

Music vs noise
Music vs. Noise matter.

  • Music

    • specific pitches and sound quality

    • regular pattern

  • Noise

    • no definite pitch

    • no set pattern

Interference matter.

  • Beats

    • variations in sound intensity produced by 2 slightly different frequencies

    • both constructive and destructive interference occur


Anechoic chamber - designed to eliminate reverberation. matter.


  • Acoustics

    • the study of sound

  • Reverberation

    • echo effect produced by the reflection of sound