http://www.lon-capa.org/~mmp/applist/doppler/d.htm
http://falstad.com/mathphysics.html
Run the Ripple tank applet -
http://falstad.com/ripple/
The key in the Doppler effect is that motion makes the
"detected" or "perceived" frequencies higher or lower.
If the source is moving toward you, you detect/measure a
higher frequency - this is called a BLUE SHIFT.
If the source is moving away from you, you detect/measure a
lower frequency - this is called a RED SHIFT. Distant galaxies in the universe
are moving away from us, as determined by their red shifts. This indicates that
the universe is indeed expanding (first shown by E. Hubble). The 2011 Nobel
Prize in Physics went to local physicist Adam Riess (and 2 others) for the
discovery of the accelerating expansion of the universe. Awesome stuff!
http://www.nobelprize.org/nobel_prizes/physics/laureates/2011/
It's worth noting that the effect also works in reverse. If
you (the detector) move toward a sound-emitter, you'll detect a higher
frequency. If you move away from a detector move away from a sound-emitter,
you'll detect a lower frequency.
Mind you, these Doppler effects only happen WHILE there is
relative motion between source and detector (you).
And they also work for light. In fact, the terms red shift
and blue shift refer mainly to light (or other electromagnetic) phenomena.
