The Universe

Evolution of the Universe

How does the Doppler effect work for sound?

Named for the nineteenth-century physicist Christian Johann Doppler (1803–1853), the Doppler effect occurs when a source of sound is moving toward or away from a listener. If the source is moving toward the listener, the sound wave’s wavelength decreases, and the frequency increases, making the sound higher-pitched. Conversely, if the source is moving away from the listener, the sound wave’s wavelength increases, and the frequency decreases, making the sound lower-pitched. The next time a car or train passes by you on the street, listen to the sound it is making as it approaches and then moves away.


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