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Speed of sound 
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#1
Nov1610, 08:05 PM

P: 10

Why does sound travel faster through warm air then cold air????
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#2
Nov1610, 08:15 PM

P: 292

If they are moving faster, then they cover a greater distance, and so are more likely to collide, which allows sound to travel quicker, as all sound is, is an increase and decrease of the local pressure. 


#3
Nov1610, 09:22 PM

P: 328

Err... I'm pretty sure sound travels faster in cold air.
For the same reason sound travels faster in iron; cold air is denser than hot air. 


#4
Nov1610, 09:31 PM

P: 3,387

Speed of sound
For every 1 degree celsius the temperature increases, the speed of sound increases by 0.6m/s.



#5
Nov1610, 10:02 PM

P: 328

I stand corrected. I suppose I should have done a little googling before posting.
But I think this is a more complicated problem than we're giving it credit. The speed of sound through a medium is directly proportional to the density and temperature of the medium, but density and temperature are inversely proportional to each other. But, if what I'm hearing is right, the increase in molecular velocity outweighs the decrease in speed. 


#6
Nov1710, 09:06 AM

P: 1,969

The speed of sound decreases when the density increases.
This is generally true for all kind of media, gas, liquid, solid. The speed increases with increased stiffness of the medium. For fluids this stiffness is usually measured by the bulk modulus; for solids by Young's modulus. The reason sound propagates faster through metals even though they are denser than gases is that they can support larger restoring forces (they are stiffer). 


#7
Nov1710, 12:28 PM

P: 10

Thanks ppl!!!!!!!!!!!!!!!



#8
Nov1710, 02:25 PM

Sci Advisor
P: 2,510




#9
Nov1710, 02:54 PM

P: 328

EDIT: Ok, I got it. Check this out. 


#10
Nov1710, 07:26 PM

P: 1,008




#11
Nov1810, 06:01 AM

Sci Advisor
PF Gold
P: 11,919

Furthermore, for solids, the speed of sound depends upon the stiffness (modulus) and the density. Faster for stiffer, slower for more dense. For two substances with the same stiffness, the more dense one will transmit sound slower. If this is counterintuitive, it's because our experience is that more dense materials are usually / often more stiff. 


#12
Apr2112, 10:24 AM

P: 4

Hey guys just did some algebraic calculation and got a strange conclusion.
since speed of sound is related to speed of molecule, we can assume they are proportional to each others. Then, according to kinetic theory equation, pV = 1/3 NMc ........(1) where c is the rms speed of air molecules, N is number of air molecules, M is mass of each air molecule. i.e. NM = total mass of the gas please notice that density of air = mass/volume, i.e. ρ = NM/V , where ρ is density therefore, by rearranging the equation, c = 3p/ρ which basically means that the speed of molecule is inversely proportional to density, assuming change in pressure is negligible, which is against most of the arguments above. 


#13
Apr2112, 11:58 AM

Mentor
P: 11,589

If you increase the density with constant pressure, you cool the gas (or replace it by a gas with heavier molecules). A lower temperature gives a lower speed of sound. Where is the problem?



#14
Apr2112, 12:31 PM

P: 4,663




#15
Apr2112, 04:06 PM

Mentor
P: 11,589

As long as all instruments in the concert are roughly at the same temperature, this shouldn't be a big problem. A (large!) temperature difference of 5°C would be a relative change of ~1.5% of the absolute temperature, while the halfsteps are about +6% at the frequency.



#16
Apr2112, 04:59 PM

Sci Advisor
PF Gold
P: 11,919

But strings don't behave like wind instruments.



#17
Apr2212, 04:07 AM

P: 1,008




#18
Apr2212, 04:11 AM

P: 1,008




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