The formula for the Doppler effect is presented in the window below. The animation on the right illustrates how the frequency of sound waves in front of a moving sound source increases and the frequency behind a moving sound source decreases.
The Doppler effect demonstration is shown in the window below. The physics student is directed to select the speed of a train and a police car which are moving towards each other. The student then may listen to the sound produced by either the train or the police car. The distinct frequency shift conveys the Doppler effect phenomena.
To listen to the doppler effect created by a passing train, press the sound button for the appropriate audion format.