Doppler effect of sound waves I am looking for interesting ways to introduce the Doppler effect to students. I want some situations in nature or every day life, where a student is possibly surprised and may ask "how could it be"?
The common example for Doppler effect of sound waves is the siren of a moving emergency vehicle. Clearly the siren example is one way to introduce it starting from a phenomenon. However are there other interesting, perhaps astonishing phenomena in nature or in every day life which can explained by Doppler effect of sound waves?
In this question I am only interested in Doppler effect of sound waves, not that one of light.
 A: There is a list on Wikipedia.
Radar guns use an optical Doppler effect to measure speed.  Their acoustic equivalent is used in medicine, where it's called Doppler ultrasound and used to measure blood flow or other sorts of motion in the body.
Animals that use echolocation can use the Doppler shift to gain information about the motion of their surroundings.
A sonic boom occurs when the Doppler shift shifts a frequency to infinity.
I guess one can continue to concoct scenarios.  I wonder whether, when you drop a cat off a cliff, you can hear the pitch of its screaming drop as  it accelerates.  (It's not all that cruel - cats can usually survive a fall at terminal velocity.)  
You could use it to determine which way a whale is swimming if you have two boats, both listening to the same whalesong.  You could even use the Doppler shift to gain information about the position of the whale because both the whale's position and its velocity contribute to the observed Doppler shift at any given place.  (I don't have any information about this actually being done, but it might be an interesting problem to work out the locus of possible whale locations for an observed Doppler shift.)
I was also curious about whether the Doppler effect gives us information on the motion of the crust that moves during an earthquake.  I found this reference which suggests it does.
A: Two suggestions from experience:


*

*Let your students stay near a highway for 10 minutes (car engine works just like siren, but many sound changes challenge their mind)

*I also notice that talking, while yawning causes me to here my own voice if lower frequencies.   

A: As a piano player, I sometimes shake my head back and forth to give myself the sensation of hearing vibrato.
A: Ship's use doppler logs to tell them how fast they are moving through the water. They are used to calculate forwards/backwards speed as well as sideways speed. Very large ships, such as super tankers, would not be able to dock safely without this equipment.
