The Awesome Power of Sound - Railroad Safety, the Doppler Effect, and the Speed of Sound
Channel: AndyMedia
Date: 2014-03-30

This video demonstrates a variation of the Doppler effect - how a freight train can be almost silent until it comes extremely close. This is because trains and other moving objects bunch up the sound waves in front of them. It can be dangerous when this happens, since you may be approaching a train and be unable to hear it. This is why you should always stop, look and listen at railway grade crossings. For more information, see Operation Lifesaver: http://oli.org/