A common example of the Doppler Effect occurs when a car, or any object emitting a sound, passes by, then there is a change in the pitch of the sound coming from the sound source. As the sound source approaches you, the sound heard has a higher pitch (higher frequency) and as the sound source moves away from you, the sound heard has a lower pitch (lower frequency). This phenomenon is known as the Doppler Effect
IMPORTANT FACTS CONCERNING DOPPLER EFFECT