The Doppler Effect is the change in frequency of a wave that results from an object’s changing position relative to an observer. A well-known example of the Doppler Effect is when an ambulance zooms by you and makes a “wheee-yow” sound. The high-pitched “whee” is caused by sound waves that are bunched together because the ambulance is moving in the same direction as the emitting sound waves. The bunching together of sound waves creates an increase in the frequency and results in a higher-pitch sound. The low-pitched “yow” sound occurs when the vehicle moves away from the propagation of the sound wave. Since the ambulance moves away from the sound wave, the spacing between successive waves becomes greater. This decrease in the frequency of the sound wave results in a lower pitch.