# SpaceShipOne in outer space video

The math is straight forward, but it's still hard to conceptualize. The atmosphere has many components and each component can vary. So regardless of the percentages of gasses in the atmosphere, like CO, CO2, O2, O3, and regardless of the dissolved water, the speed of sound remains constant. These constituents change the density, but do not change the speed of sound.
Likewise, the speed of sound is the same at the north pole at sea level at -60F, as it is on top of mount Everest at -60F. Although the air is much denser at the north pole, the math says that the speed of sound is the same.
Right?
At Smoke Creek we used to fly mach rockets over our heads so we could "feel the boom". Perhaps that strategy could be used to get more proximate reading of shock velocities.
Jerry
Safety is purely optional.
Humm, I smell a science project that measures the speed of sound at 72 degrees in both 10% and 97% humididy at 800 feet about sea level.
hmmmm did not know this.
I never bothered to see what it was in the same medium (IE air at different temps)
they why is sound faster in steel than air even at the same temp ?
Chris Taylor
"David Weinshenker" wrote in message > No, you have it backwards.
Computations
At pressures or temperatures where air does not behave as an ideal gas there'll be nobody alive to argue the point.
Do you have a hard time with the concept of "exact"?
Steven P. McNicoll wrote:
Nope. Why do you have such a hard time with the concept of "irrelevant"?
I understand quite well that (1) irrelevant discrepancies do not render a relationship exact, and (2) your idea of irrelevant may be quite different from someone else's, particularly someone capable of precision measurements.
Steven P. McNicoll wrote:
I don't think you do.
Chris, I too was taught in my physics class many decades ago that SOS in air was based on density. This same teacher and I got into an issue of fatter tires on cars not providing more traction. I.e. he said that fat tires did not provide anything other then looks. I guess all the race car engineers are wrong.
he used the standard fish scale pulling a red brick on both the fat and the skinny side accross a wooden lab table showing the same about of force required.
If he had used a block of tire rubber weighted down on an asphalt surface, he might have seen the difference.
anyway, I found this that explained it to me as Steven just know woke me up to this most interesting fact.
BTW, thanks Steven for sparking the info exchange.
So, what you're saying is that atmospheric pressure is constant from 36K to 70K feet?
Doug I'll never correct Tod again....
I ran the numbers for dry air at 20 deg. C and found that the ideal gas law differs from the accepted speed of sound in dry air at that temperature by about 0.02 percent (0.0002). Because the molecular weight of water and the gamma differ significantly from dry air, it is important to specify dry air. I read one place
that water vapor has a speed of sound of 402 m/s at 35 C where dry air should be 352.1 m/s.
Steven P. McNicoll wrote:
thankyou for the info. no time right now to read it but I saved it locally and will read it (now I am deadly curious about it :-)
Chris Taylor

does not pressure effectively deal with density in this scenario ? (I am trying to understand this :-)
IE squeeze more air in a fixed amount of space and that space IS more "dense" than the same volume with less atmosphere in it ?
Chris Taylor

That's where I was going with 100% vs 0% humidity and smog. (I'm not the argumentitive type.)
He is correct, for a STATIC friction surface. The weight of the car or brick remains the same, thus the force on the surface remains the same. The smaller surface has a higher force per square unit area and the larger surface has a smaller force per unit area. The two different forces are canceled out by the relationship of the unit area to the friction. In other words, the smaller surface area has less friction, but more force per square inch and is exactly equal to the larger surface having more friction but less force per square inch.
However, care tires are dynamic. The friction changes as the tires heat up but more importantly, the torque imparted to the tire causes a higher load in the front of the tire. (ever see the tires on a dragster "wrinkle?) A small tire must have higher pressure. Higher pressures "stiffen" the tire, not allowing it to transfer the torque to the friction area.
That's only part of the reason. The Bowden/Tabor model of friction applies to most things, but doesn't really apply very well to elastomers.
I realize I'm getting old when I can recall attending lectures from both Bowden and Tabor. Tabor was my lab intructor in freshman physics.
J
yep, thanks for that explanation. I figured out years ago something different , but similar.
It's nice to hear the true reason.
he just didn't like Race Cars BTW.

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