How does the doppler effect work?

The Doppler Effect is an observed change in the frequency
of any wave when the source of the wave is moving. When the source of a wave moves
toward the observer, each disturbance reaches the observer in a time less than the
previous disturbance one. And when the source moves away from the observer the time
taken for each disturbance to reach the observer is more than the earlier one. This
causes an increase in the frequency of the wave when the object and source are moving
closer for a href="http://www.exploratorium.edu/hubble/tools/doppler.html">blueshift and
a decrease in the frequency when the object and source are moving away from each other
for a href="http://www.exploratorium.edu/hubble/tools/doppler.html">redshift. The
Doppler Effect can be observed in all types of waves like sound, light, etc. One popular
application of the Doppler Effect is in measuring the speed of
objects.