frequency than the source emitted. In the same way, if the source moves toward the
detector, the wavefronts pile up, and this results in the detector receiving waves
with shorter wavelengths and higher frequencies.
Note that when the detector moves and not the source, there is no change in
wavelength. Instead, there is a change to the speed with which the detector receives
wavefronts.
Conversely, if the detector is moving away from the source or if the source is
moving away from the detector