Doppler Effect

Sound from a moving source sounds different than from a stationary source.

If the source is moving toward you, the sound will be higher in pitch.

If the source is moving away from you, the sound will be lower in pitch.

This is known as the Doppler effect.

If the source is moving toward you, the sound will be higher in pitch.

If the source is moving away from you, the sound will be lower in pitch.

The details are given by the equation

where f' is the frequency that is heard with a moving source (or observer), f is the frequency heard with source and observer at rest, v is the speed of sound, vobs is the speed of the observer, and vsource is the speed of the source.

[ Be careful with the sign conventions!

For

A police "radar gun" uses the Doppler Effect to measure the speed of a moving vehicle by detecting the frequency of the waves reflected by the vehicle.

Beats

Sonic Boom
Return to ToC, Waves and Sound
(c) 2002, Doug Davis; all rights reserved