high School⏱ 4 min

Doppler Effect

Why a passing siren changes pitch

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ahead: 1.71×fbehind: 0.71×f

Parameters (c = wave speed)

f′=f \ raccc∓vzf' = f\,\ rac{c}{c \mp v_z}

• Ahead of the source the wavefronts bunch up -> higher frequency • Behind they stretch out -> lower frequency • That is why a passing siren changes pitch