The Doppler effect

Have you ever been standing by the side of the road as a speeding ambulance approached, siren wailing? You may have experienced the Doppler Effect. As you stood still, you heard the wail of the siren, a high- pitched noise. As the ambulance came up beside you, the sound of the siren changed to a much lower pitch. Then, as the ambulance sped by, the sound of the siren became high-pitched again. In this example, the course of the sound waves was moving and the observer was stationary.
Christian Johann Doppler, an Austrian physicist, defined the Doppler Effect. He was born in Salzburg, Austria. He graduated from the Polytechnic Institute of Vienna, and his primary interests were mathematics and physics. In 1842 he presented his paper describing the Doppler Effect, at a meeting of the Royal Bohemian Society of Sciences, in Prague. Doppler’s main intent of this experiment was to figure out why a sound coming towards you seems to get louder than a sound that is moving away from you....