Doppler+Effect

  Doppler Effect

media type="file" key="Doppler.mov"

 
 * Definition**- A change in the observed frequency of a wave, as of sound or light, occurring when the source and observer are in motion relative to each other, or when just the source is in motion while the observer is stationary.

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 Here are some small clips that help explain the definition of Doppler Effect.

Stationary Sound Source


The movie above shows a stationary sound source. Sound waves are produced at a constant frequency //f//0, and the wavefronts propagate symmetrically away from the source at a constant speed //v//, which is the speed of sound in the medium. The distance between wavefronts is the wavelength. All observers will hear the same frequency, which will be equal to the actual frequency of the source.

Source moving with vsource < vsound ( Mach 0.7 )
In the movie above the same sound source is radiating sound waves at a constant frequency in the same medium. However, now the sound source is moving to the right with a speed //vs// = 0.7 //v// (Mach 0.7). The wavefronts are produced with the same frequency as before. However, since the source is moving, the center of each new wavefront is now slightly displaced to the right. As a result, the wavefronts begin to bunch up on the right side (in front of) and spread further apart on the left side (behind) of the source. An observer in front of the source will hear a higher frequency //f// ´ > //f//0, and an observer behind the source will hear a lower frequency //f// ´ < //f//0.


 * http://www.kettering.edu/~drussell/Demos/doppler/doppler.html** Credit to Professor Dan Russell



