Here's how it works:
* Moving towards you: As the sound source approaches, the sound waves are compressed, resulting in a higher frequency and a higher pitch.
* Moving away from you: As the sound source moves away, the sound waves are stretched out, resulting in a lower frequency and a lower pitch.
This phenomenon is why an ambulance siren sounds higher pitched as it approaches you and lower pitched as it moves away. The Doppler effect also applies to light waves, which is how astronomers can determine the movement of stars and galaxies.
