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Why does the Doppler effect have different expressions for a moving source and a moving observer if movement is relative? Shouldn't the expressions for a source coming closer to the observer and the observer coming closer to the source, for example, be the same?

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    $\begingroup$ The medium is moving in one case and not the other... $\endgroup$
    – Floris
    Oct 5, 2017 at 19:12
  • $\begingroup$ The medium is moving? What do you mean? Isn't it the source that is moving and observer? $\endgroup$
    – Gabu
    Oct 5, 2017 at 19:15
  • $\begingroup$ In the reference frame of the observer, it's the medium that's moving. $\endgroup$
    – stafusa
    Oct 5, 2017 at 19:20
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    $\begingroup$ It might help to clarify that the Doppler shift for waves that propagate in a medium depends on the motion of both source and observer relative the medium. The Doppler shift for light (which does not propagate in a medium) depends only on the relative motion of the source and observer, and so it agrees with your intuition. $\endgroup$ Oct 5, 2017 at 19:44

1 Answer 1

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Why does the Doppler effect have different expressions for a moving source and a moving observer

It does not, simplifications of the effect may have such expressions. The full form requires the velocity of the source and observer relative to the medium.

I am sure you have seen this in "real life". You have heard the sound of a siren as it passes you. Have you heard that same thing in a strong wind?

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    $\begingroup$ I think this answer would be stronger if you actually showed the equations you are referring to. $\endgroup$
    – Floris
    Oct 5, 2017 at 21:43
  • $\begingroup$ I would like to see them too. A possible link to a derivation would be nice too. Thank you. $\endgroup$
    – Gabu
    Oct 6, 2017 at 22:57

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