As for the Doppler effect, there is only one change in pitch. The pitch changes because the sound waves get "squeezed together" when the source of the sound is approaching, so when something that makes a sound approaches you, the pitch of the sound is higher. Then when it recedes from you, the sound waves get "stretched out", and the pitch is lower. The echo itself has nothing to do with the Doppler effect. An echo is an echo... anyone care to explain what an echo really is, scientifically speaking? Eh... I think Elisabeth just did.
And Sue!!! You don't like my government conspiracy theory???? WHAT??? Okay, I'll stick with a previous theory, then. It's the Bermuda Triangle! I mean, it's the Nevada triangle!
Ann
