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Formula Acoustic Doppler Effect Observer frequency    Emitter frequency    Emitter speed    Observer speed

Formula
Formula: Acoustic Doppler Effect
Doppler-Effekt - zulaufende & weglaufende Beobachter
Doppler-Effekt - zulaufende und weglaufende Beobachter

Observer frequency

Unit
Frequency perceived by an observer (who may hear a loud ambulance, for example).

Emitter frequency

Unit
Frequency emitted for example by the siren of an ambulance.

Speed of sound

Unit
Speed of sound at which sound waves propagate. In air, the speed of sound is: \( c ~\approx~ 340 \, \frac{\text m}{\text s} \) at 20°C.

Emitter speed

Unit
Speed at which the emitter (for example an ambulance) moves relative to the observer.

"\( c ~-~ v_{\text s} \)" is used when the emitter moves towards the observer. "\( c ~+~ v_{\text s} \)" when the emitter is moving away from the observer. If the emitter is stationary, then \( v_{\text s} = 0 \).

Observer speed

Unit
Speed at which the observer moves relative to the emitter.

Use "\( c ~+~ v \)" when the observer moves towards the emitter. "\( c ~-~ v \)" when the observer moves away from the emitter. If the observer is standing still, use \( v = 0 \).