The Doppler Effect

The shift in a wave's observed frequency is due to the relative motion between the source of the wave and an observer. As a car beeps its horn while traveling, it has a constant frequency and as the velocity increases, the sound waves from the observer have lower amplitudes and are less frequent. This is known as the Doppler effect. As sound waves come toward the observer they have higher frequencies than the sound waves moving away from the observer. Not only does frequency help explain the Doppler effect but it also explains how the police are able to find the speed of cars on a highway. A radar gun can be used to determine the speed of a car by measuring the different frequencies between emitted and reflected radar waves!