Question

How does the Doppler effect explain the sound you hear when a race car comes toward and then passes a camera?

Answer 1

when an object is moving the waves in front of it (sound, light, whatever) get compressed and the waves behind it are stretched apart. so in a race cars case, the compressed waves make a higher pitched noise and vice versa

Answer 2

The pitch is higher as it approaches and then becomes lower the moment it passes.