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Sound
Physics
Spring 2002
Sound waves
Longitudinal or compressional waves Sound waves move through a medium Sound waves move faster through a
solid than a liquid and slowest through gases
Pitch is related to frequency Loudness is amplitude
Pitch
The frequency of sound is called a note. Two notes with frequencies of 2:1 are
one octave apart. – 220 Hz is one octave away from 440 Hz
and two octaves away from 880 Hz “C” has a frequency of 262 Hz
Loudness Loudness is measured in decibels
– Decibels are a ratio of the intensity of a sound to the intensity of the most faintly heard sound.
– A sound with ten times the intensity will only sound twice as loud.
The loudest intensity we can bear without pain is 1012 times greater than the faintest whisper we can hear. – Approximately 160 dB
The Ear
Outer ear: Fleshy visible part that collects sound, ear canal, and ear drum
Middle ear: Three tiny bones in an air filled space which transmit sound from the ear drum to the inner ear
Inner ear: Transmits sound through a watery liquid to the tiny hair cells in the cochlea.
Doppler effect
Frequency seems higher if sound is coming toward you.
Frequency seems lower if sound is moving away from you.
Frequency from the source does not change.