Doppler EffectSound 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 movingtowardyou, the sound will behigherin pitch.

If the source is movingaway fromyou, the sound will belowerin 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, v

_{obs}is the speed of the observer, and v_{source}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

(c) 2002, Doug Davis; all rights reserved

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