Doppler effect: when a source of a sound and a listener are in motion relative to each other, the frequency of the sound heard by the listener is different from the source frequency.
Doppler Effect—moving listener, moving source
Doppler Effect—Electromagnetic waves
c is the speed of light, and v is the relative speed of the receiver to the source. v is positive when the source is moving towards to receiver.
If the source speed relative to the medium exceeds the speed of sound in the medium, the Doppler equation no longer applies. Shockwaves result. The half angle of the wavefront is given by,
is called the Mach number.
