When you hear a police siren, the sound seems to rise and fall. What is most likely responsible for this perceptual experience?

Question

Quizplus · Accepted Answer

This perceptual experience is due to the Doppler effect, which is a change in frequency (and wavelength) of a wave in relation to an observer who is moving relative to the wave source. As the police siren moves towards you, the sound waves are compressed, leading to a higher pitch (frequency), and as it moves away, the waves are stretched, leading to a lower pitch.

When You Hear a Police Siren, the Sound Seems to Rise