- #1
Soren4
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I would like to be sure about one case of the use of Doppler effect with sound waves.
If the medium (in the case of sound air) is moving, but there is no relative motion between the observer and the source there is no Doppler effect at all. (And the absence of relative motion is frame-indipendent)
So imagine we have source and observer steady relative to ground and air moving. The speed of sound in frame of reference of the ground changes, but this does not mean that frequency of the wave changes, just that it wavelenght is different. So in such case frequency does not change at all, but, ##v_{sound}## changes. And this imply that ##\lambda## changes too.
Is all of this correct, or is there something conceptually wrong?
I'm a bit confused because I found a similar situation in a exercise, which I write here.
A guitar player is playing in front of crowd. There is wind blowing at speed ##v## from the stage to the crowd. If the frequency of sound waves is ##f## what is the frequency perceived by the crowd?
If all I said is correct then there should not be any change in frequency, nevertheless in the solution of this exercise I found this $$f'=f(\frac{c+v}{v})$$ So it is interpreted as the crowd comes closer to the source.
I think this resolution is wrong, because it contradicts what said above.
I would really appreciate any suggestion
If the medium (in the case of sound air) is moving, but there is no relative motion between the observer and the source there is no Doppler effect at all. (And the absence of relative motion is frame-indipendent)
So imagine we have source and observer steady relative to ground and air moving. The speed of sound in frame of reference of the ground changes, but this does not mean that frequency of the wave changes, just that it wavelenght is different. So in such case frequency does not change at all, but, ##v_{sound}## changes. And this imply that ##\lambda## changes too.
Is all of this correct, or is there something conceptually wrong?
I'm a bit confused because I found a similar situation in a exercise, which I write here.
A guitar player is playing in front of crowd. There is wind blowing at speed ##v## from the stage to the crowd. If the frequency of sound waves is ##f## what is the frequency perceived by the crowd?
If all I said is correct then there should not be any change in frequency, nevertheless in the solution of this exercise I found this $$f'=f(\frac{c+v}{v})$$ So it is interpreted as the crowd comes closer to the source.
I think this resolution is wrong, because it contradicts what said above.
I would really appreciate any suggestion