I’m trying to understand the concept of relative velocity in the context of sound waves. When sound travels from a source to a receiver, I’m confused about how to calculate the wave’s velocity relative to the source (vwm). The equation Vfm = 80 m/s represents the velocity of the medium moving at a constant relative to the medium. Now, if I want to find the velocity of the medium moving from the source, why do I have to add up the velocity of the wave relative to the source and the velocity of the source relative to the medium? Also, when should I use the velocity of the medium relative to the source, and when should I use the velocity of the source relative to the medium?”
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I can’t tell if you understand this already, but when you’re thinking about the concept of relative velocity you’re asking about:
A sound wave is a wave of pressure moving through the air. If you were standing still, the sound wave from the source will pass by you in the air. The pitch that you hear the sound at is a result of the frequency of the wave, or technically how fast the air pressure is varying around your ears as the wave passes by. Now you can think of a sound wave behaving just like a wave in the ocean. If you’re just in the water floating, the wave passes over you quickly. If you were to swim in the direction of the wave you’ll be “in it” for a longer time. This is basically the Doppler effect – when you’re moving away from the source, as the sound wave is passing you you are moving along with it, so the pressure is changing a bit slower around your eardrums than if you were standing still and it drops the pitch.
I don’t know if you already understood that, sorry if you did, but it might help in understanding why those equations from the other great posts work.
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