The discussion centers on the significance of relative velocity in the Doppler effect, specifically addressing the confusion surrounding frequency changes when a sound source moves towards a listener. The correct Doppler formula for an approaching source is given as f' = (v / (v - v_s)) f, where v_s is the speed of the source. The participants clarify that the relative velocity of the source and observer does not directly factor into the Doppler formula, as the speeds are relative to the medium (air) rather than each other. Understanding this distinction is crucial for accurately applying the Doppler effect in practical scenarios.
PREREQUISITESPhysics students, educators, and anyone interested in understanding wave behavior and the Doppler effect in sound and other mediums.
What does the Doppler formula give you for the observed frequency when the source is moving? Not sure what you mean by "total velocity"--realize that the source is moving towards the listener.PsychonautQQ said:I don't understand how it increases it's frequency by a factor of 10, I mean the total velocity goes from 1 to 1.9, therefore It seems like it should increase from 1kHz to 1.9kHz. Why is my 'common sense' wrong?
No.PsychonautQQ said:frequency receiver = (velocity sound + velocity sender) * frequency sender
with velocity of sound = c and velocity of sender = .9c, It seems the frequency received is 1.9 the original frequency. No?
Note that relative velocity (of source and observer) doesn't enter into the Doppler formula (at least for sound). The speeds are relative to the air. And that a moving source differs from a moving observer. (Compare the two cases, even for the same speed.)PsychonautQQ said:Okay so the correct Doppler effect the source is in the denominator, I don't understand qualitatively why it matters though. Whether it's the receiver or sender that's movie, the relative velocity between them is going to be the same?