Have you ever noticed that if a car with a horn blowing is moving past you rapidly that the sound waves emitted by the horn seems to change frequency? In 1842 an Austrian physicist, Hans Christian Doppler, observed and analyzed the same phenomenon for sound emitted by a passing train. Hence the phenomenon is known as the Doppler Effect.

A similar effect is found for the propagation of light and other electromagnetic waves from moving sources. In fact highway patrol officers use radar to measure Doppler shifts in radio waves so they can determine how fast vehicles are moving.

In this activity, you will work with movies of a honking car moving fairly rapidly on a straight level road past a stationary microphone.



In this activity, you will

  • Verify that the Doppler Equations can be used to predict the ratio (fF / fB) of the apparent car horn frequencies before and after the car passes the microphone.