Physics
Advanced

Doppler Effect

Observed frequency shift due to relative motion.

Formula

f′=fv±vov∓vsf' = f\frac{v \pm v_o}{v \mp v_s}

Variables

fSource frequency
vWave speed
v_o,v_sObserver/source speeds

Example

An ambulance siren rises in pitch as it approaches, then drops as it passes — the Doppler effect.

Did You Know?

The Doppler effect — the drop in a passing siren's pitch — also lets astronomers measure the universe's expansion.

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