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.