FearOfPhysics.com: What is the Doppler Effect for Sound

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What is the Doppler Effect for Sound

To start, let's borrow an idea from the pages about sound: what a wave is. But instead of all of the fancy graphics, we'll draw the waves like this:

Here, the blue "waves" that go out are the pushes in the air that your ears respond to. The red dot at the center is a speaker pushing the air (producing the sound).

Ok? So to proceed with the Doppler Effect, look at the above animation and ask yourself:

"What would happen if the red dot was moving towards or away from my ear?"

This is a perfectly legitimate question. The red dot could be a police car moving with its siren on, or a person who is running while blowing a whistle.

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