Quote:
Actually, the speed of sound is neither a constant, nor is it just the "speed that sound can travel at". The speed of sound varies with the physical makeup of the medium and its temperature.

so does g 9.8m/s^2
but we use it as a constant --- ACTUALY---
whats your point other than nic picking.


As I mentioned earlier, my point was dishonestly cropped by you. But this point is worth revisiting, and as such here is a separate post...

The speed of sound in a given gas is determined by:
S = sqrt(C/d), where
S = speed of sound
C = elastic/bulk modulus of the gas/gas mixture,
1.42×10^5 Pa for air at STP
d = density

The density of a gas is dependent on pressure:
d = p/RT, where:
d = density
p = absolute pressure
R = specific gas constant, for dry air this is
287.058J kg−1 K−1
T = temperature, in kelvins

So at 100PSI, at room temp, the density of your gas is:
d100 = p/RT
d100 = 689,475Pa/(287.058J kg−1 K−1 * 293K)
d100 = 8.2 kg/m^2

and the speed of sound is:
S100 = sqrt(C/d)
S100 = sqrt(1.42×10^5 Pa/8.2 kg/m^2)
S100 = 131.61 m/s

At atmospheric pressure (14.7PSI):
d14 = 101,352Pa/(287.058J kg−1 K−1 * 293K)
d14 = 1.2 kg/m^2

thus the speed of sound is:
S14 = sqrt(1.42×10^5 Pa/1.2 kg/m^2)
S14 = 343.28 m/s
---------------------------------
At this point you're probably asking "WTF is the point?"

The point is simple, and two-fold:
1) Contrary to your claims, the speed of sound is not a constant. In fact, it will be roughly three times SLOWER in your pressurized tank than it will be in your pipe.

2) You've mistakenly tried to calculate the force generated by your system, using m*v where m is the mass of the air, and v is the speed. You're wrong two ways here - m*v in using your measures gives you momentum, not force. And on top of that not-so-insignificant foopah, your v is wrong - its restricted to the speed of sound of the gas, due to back pressure. In the case of your 100PSI tank, that's 131.61 m/s.

So two basic claims of yours - the second of which is te foundation of your "proof" my math is wrong - are in and of themselves 100% wrong.

Kinda like your whole argument, beginning to end...

Bryan

Last edited by ImagingGeek; 06/09/10 02:07 AM.

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