Science Questions

If wind has zero resistance, does it make a sound?

Sat, 16th Oct 2010

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Ken asked:

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.



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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.

Or maybe not, if you take light from a a laser and send it on a surface it will still make a sound, Awh sh :) Can't decide on that one. It's more or less what conducts the sound that will decide it, the medium as it is, that momentum can 'push' like light does will create a vibration in what it 'pushes' on, but that vibration will meet resistance in matter, and if there are no resistance meet, then it can't be matter as we ordinary define it, and then I expect that there won't be any sound to it either. So, I think my first response was correct.

The thing that I believe to make the sound is of course atoms and molecules etc in that medium, matter that is. You can get supra conducting in certain materials, when cooled down sufficiently, and then you are thinking of the electromagnetic force primary I guess, finding no resistance. But how that really work we don't really know as I understands it, we have theories to why electrons seems to meet no, or very little, resistance, but it is still matter being there, even though they get some properties that we normally only expect from bosons, and bosons are light like particles, so?

And The theory describes superconductivity as a microscopic effect caused by a "condensation" of pairs of electrons into a boson-like state 

Why I say they are still matter is very simple. If they weren't matter they shouldn't be there when closing of the cooling of the material. The conversion of matter to bosons is quite costly, but the conversion from bosons back to matter is even worse, and takes very high energies for a very small return in form of matter, mostly a few particles getting created. So? yor_on, Mon, 13th Sep 2010

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.

Simply, wind cause turbulence that you can hear... wind is a flow of particles of air...

If all particles of air are flowing in the same direction and they encounter no resistance (no ground, nothing...) there is no sound obviously... CPT ArkAngel, Mon, 13th Sep 2010

If the wind encounters no resistance then there's no microphone or ear there.
How could you know if it made a sound?
How could it matter? Bored chemist, Mon, 13th Sep 2010

Hmm, think I got it. Liked the answer there Bored chemist.
Kind'a Zen.

And now mine.
What is the sound of light?

O0ps :) yor_on, Mon, 13th Sep 2010

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