If wind has zero resistance, does it make a sound? Since we can't see wind, only the things it moves, I would think we could not hear wind, unless it his some kind of mater which causes turblence.
Dave - It certainly won't cause any sound if there's nothing to cause any turbulence, if thereís no vibrations because sound is just a vibration of air. So, if the wind is flowing past something and that thing makes it vibrate, like if you get some swirling when it blows across the edge of a surface or something, you get some turbulence or that turbulence can drive vibrations in a bottle or something when you blow across the top of a bottle, you produce very loud sounds. If you're in a middle of an air column, so if you're up high in the air where all the air is moving the same direction very fast, there is no relative movement, so you won't get any vibrations at all. It would be very quiet. So people hot air ballooning is very, very still, even if the wind is quite high because they're moving with the wind. However, thereís various interpretations of what he means by resistance. One of them is how gloopy it is, how viscous the fluid is.
Ben - So thatís sort of the internal resistance of the fluid itself, rather than it interacting with say, a wall. This is resistance inside the fluid.
Dave - Thatís right. Basically, how much friction there is inside the fluid itself and fluids which are very, very viscous, things like treacle will move very, very smoothly, and you won't get any vibrations and itíll essentially be very, very quiet. However, if thereís very, very low viscosity, it can't lose energy by viscous flow by friction. It can only lose it by turbulence. airflows being incredibly turbulent and very, very noisy.
Ben - So that goes back to what Fred was saying about how you have to put energy in to create turbulence and then it actually loses the energy back to this internal friction.
Dave - Thatís right and the more viscosity there is, the quicker the turbulence will die away, and if thereís enough it won't form in the first place.
Ken asked the Naked Scientists: If wind has zero resistance, does it make a sound? Since we can't see wind, only the things it moves, I would think we could not hear wind, unless it his some kind of mater which causes turbulence. What do you think? Ken, Sun, 12th Sep 2010
Anything without resistance should be soundless, just like I would expect space to be. But if it has no resistance it's not there, just like space. So what you are thinking of is two things that you mix, some property like space, but calling it air.
sound is variation of pressure in a medium, gas, liquid or solid. In order to hear it, the variation of the pressure in time (frequency) has to be within your hearing frequency range. http://en.wikipedia.org/wiki/Sound
If the wind encounters no resistance then there's no microphone or ear there.
Hmm, think I got it. Liked the answer there Bored chemist.