What Is the Doppler Effect?

By jamie

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4. Passing Traffic

You likely experience the Doppler effect in action quite regularly without even realizing it. For example, you will likely have noticed how, when stood by a roadside, the sound of speeding vehicles and/or sirens changes as they go past. As they approach, they will have a higher pitched sound and the pitch will drop once the car has passed. Nothing is changing about the sound being emitted from the car; if you were in the car yourself then you would notice no difference because there is no difference.

For the person standing on the side of the road, the difference in tone as the car passes is down to the way that soundwaves are pushed closer together as the car approaches, and then stretch out once the car has passed.

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