Why does the Doppler Effect vary depending on if it is the source or the observer moving

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We were doing some physics problems with sound and the Doppler effect today. One problem had two scenarios where one was source moving away and the other was the listener moving away. The math gave two answers that were close but not the same. I don’t understand how they can be different when speed is relative.

In: Physics

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Anonymous 0 Comments

The basic notion of a doppler effect is that when a source and observer move towards one another, each successive wave crest/trough is generated closer so the frequency rises. The same principle applies for moving further away. In this case, it doesn’t matter whether the source or observer is moving. Indeed, they are fundamentally the same thing because all you have is a relative velocity between the two.

This gets muddied when you add a medium because you have two relative velocities instead of one. You have the relative velocity of the observer to the medium and the relative velocity of the source to the medium. So you have a doppler effect from source to medium, multiplied by a doppler effect from medium to observer.

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