The source of a sound is moving away from an observer who is standing still. How do the sound waves received by the observer compare with those emitted by the source?

Question

Quizplus · Accepted Answer

Because the sound is moving away from the observer, it takes longer for each sound wave to reach them, increasing the distance between each wave. Since increasing the wavelength of a sound decreases its frequency, the observer will perceive the source of sound as having a lower and lower frequency over time. This phenomenon is called the Doppler effect, and can occur any time the source of a sound moves closer to or further away from an observer.

The Source of a Sound Is Moving Away from an Observer