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~ Sound ~. The Nature of Sound Speed of Sound Human hearing Doppler effect “Seeing” with 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

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sound
~ Sound ~

The Nature of Sound

  • Speed of Sound
  • Human hearing
  • Doppler effect
  • “Seeing” with sound
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
human hearing
Human Hearing

sound wave

vibrates ear drum

amplified by bones

converted to nerve impulses in cochlea

human hearing1
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

human hearing2
Human Hearing
  • Intensity
    • volume of sound
    • depends on energy (amplitude) of sound wave
    • measured in decibels (dB)
human hearing3
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
seeing with sound

Medical Imaging

SONAR

“SoundNavigationRanging”

“Seeing” with Sound
  • Ultrasonic waves - above 20,000 Hz
sound problems
Sound Problems
  • vs = D ÷ T

where vs = speed of sound 344 m/s

D = distance in m

T = time in s

  • vs = f x λ, just like a wave problem!
ex 1 find the wavelength of a 200 hz sound
Ex #1:Find the wavelength of a 200 Hz sound.

GIVEN:

vs = 344 m/s

f = 200 Hz

λ = ?

WORK:

vs = f x λ

λ = vs ÷ f

λ = 344 m/s ÷ 200 Hz

λ =1.7 m

ex 2 if you hear a sound 3 s after you see the motion how far away is it
Ex #2: If you hear a sound 3 s after you see the motion, how far away is it?

GIVEN:

vs = 344 m/s

T = 3 s

D = ?

WORK:

vs = D ÷ T

D = vs x T

D = 344 m/s x 3 s

D =1032 m

music
~ Music `

Music vs. Noise

Resonance

Harmonics

Interference

Acoustics

music vs noise
~ Music vs. Noise `
  • Music
    • specific pitches and sound quality
    • regular pattern
  • Noise
    • no definite pitch
    • no set pattern
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
resonance2
= Resonance =

“Galloping Gertie”

The Tacoma Narrows Bridge Disaster

Wind through a narrow waterway caused the bridge to vibrate until it reached its natural frequency.

harmonics
} Harmonics }
  • Fundamental
    • the lowest natural frequency of an object
  • Overtones
    • multiples of the fundamental frequency
interference

Constructive - louder

Destructive - softer

| Interference |
  • Interference
    • the ability of 2 or more waves to combine to form a new wave
resonance3
= Resonance =
  • 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