Answer :

AL2006

That change in pitch can be described by the math
of the Doppler effect.    But that doesn't 'explain' it.

The correct answer is:

Doppler effect

Explanation:

The Doppler effect is the variation in wavelength or wavelength of a wave in relative to an observer who is moving to correspond to the wave source. It is described after the Austrian physicist Christian Doppler, who explained the phenomenon in 1842.


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