Chapter 15 Sound

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Chapter 15 Sound
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15.1 Properties of SoundSound Waves

• longitudinal wave
• mechanical wave
• has properties similar to water
• reflection
• refraction
• diffraction
• interference

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• Produced by vibrating matter that cause the
  medium to have high pressure (compressions) and
  low pressure (rarefactions)
• speed depends upon ????
• Speed of sound in air depends on the temperature
  of the air

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• 331 m/s at 0o C
• for every 1o C the speed changes by 0.6 m/s
• goes up if temperature goes up and down if
  temperature goes down

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Detection of Pressure Waves

• Sound detectors convert the KE of the vibrating
  matter into other forms of energy.
• Microphone- Sound KE into electrical energy
• Human ear- Sound pressure waves into electrical
  impulses

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Perceiving SoundPitch Loudness

• Physical characteristics of sound waves are
• frequency
• amplitude

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• Humans detect sound with our ears. Sound
  characteristics are defined in terms of what is
  perceived
• frequency is pitch
• amplitude is loudness

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• Marin Mersenne Robert Hooke
• connected pitch with frequency
• Pythagoras
• musical scales are based on his work

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• Most people hear sound in the range of 20 Hz to
  16,000 Hz
• Older people lose the ability to hear the higher
  ranges above 8,000 Hz

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Amplitude

• Sound waves amplitude would cause a pressure on
  the ear drum
• human can detect amplitudes of less than one
  billionth of an atmosphere

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• At the top end of the audible range the pressure
  can cause pain a million times greater than the
  lower end but still one one-thousandths less than
  one atmosphere

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• Because of the wide range in pressure variations,
  sound pressures and measured by a quantity called
  sound level
• Sound level is measured in decibels
• Barely audible 10 dB
• Jet Engine 140 dB

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• Loudness is the human perception and depends
  upon both sound frequency and sound level

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The Doppler Effect

• The change in pitch of a source because of the
  motion of either the source, the receiver, or both

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• If the source and receiver are moving closer
  together then the frequency would be higher
• frequency would be lower if they are moving apart

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• Applications of Doppler Effect
• radar detectors
• baseballs, cars, tennis balls
• astronomers
• determine speeds and distances of distant
  galaxies
• physicians
• ultrasound
• bats catch flying insects