Why does the pitch of an airplane sound like it goes from high to low when it flies overhead?

Question

Why does the pitch of an airplane sound like it goes from high to low when it flies overhead?

In: Physics

Answer 1

Doppler effect. As the waves are emitted from a different distance to the observer every time (since the source is moving) this creates an apparent change in wavelength to the observer, shorter as it’s moving towards you (high pitch) and longer as it moves away from you (lower pitch)