Final answer:
The pitch of a car's whine changes due to the Doppler effect as it passes by. The greater the pitch shift, the faster the car is moving. Estimating speed based on pitch is not as accurate as radar or speedometers.
Step-by-step explanation:
The change in pitch of a car's whine as it passes you is caused by the Doppler effect. The Doppler effect refers to the change in frequency (and therefore pitch) of a sound wave as the source of the wave moves relative to an observer. When the car is approaching you, the pitch of the whine will be higher because the sound waves are compressed. As the car passes you and moves away, the pitch of the whine will be lower because the sound waves are stretched.
The speed of the car can be estimated based on the change in the pitch of the whine. The greater the pitch shift, the faster the car is moving. This is because the pitch shift is directly proportional to the speed of the car. For example, if the pitch of the whine increases by a small amount, the car is moving at a slower speed. If the pitch increases by a larger amount, the car is moving at a faster speed.
It's important to note that estimating the speed of a car based on the pitch of its whine is not as accurate as using more precise methods such as radar or speedometers. However, it can give you a rough estimate of the car's speed.