A fire engine is rapidly approaching the corner. Explain what happens to the frequency of the sound wave as the fire engine draws closer. What do you hear?
You
will observe a higher apparent frequency because as the source moves
closer relative to the observer the wavefront emitted will be closer to
the wavefront previously emitted therefore shorter wavelength (in front
of the source only) and since the speed of sound in air is assumed
constant the frequency must increase.
