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# Ballistics Question?

#8
04-23-2008, 11:19 PM
 Platinum Member Join Date: Sep 2004 Location: on the rifle range in Utah Posts: 2,723
As Jwp pointed out, the speed of sound changes with temperature regardless of the medium. Sound actually travels faster in water than air (nitrogen, oxygen mix) and it will be faster in warm air than cold air.

So here's a brain teaser, if the temperature at 12,000 feet is 70 degrees and the temperature at sea level is 70 degrees, what will be the speed of sound at both elevations??
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#9
04-23-2008, 11:36 PM
 Platinum Member Join Date: Mar 2007 Location: MN Posts: 1,218
GG, according to JBM calc, the speed of sound is the same at both altitudes and 70 degrees. To be honest, at first I found that hard to believe, but upon reflection, the only difference in altitudes would be the force of gravity causing compression on the molocules (very very little difference). The biggest change (for the elevation that you mentioned) is going to be temp which affects the distance between molocules which has a direct affect on the time it takes for vibrations to travel from one molocule to another. Air has very little mass, so gravity will play a smaller role as long as we are talking only a few thousand feet.

Thats a good question though, 14.7 PSI is standard atmosphere at sea level and it takes how many feet of air to create that much pressure??? how high is the atmosphere anyway??? So actually the higher we go, the slower the speed of sound would be because as the air gets thinner it will be less "packed down". Sound doesn't travel at zero gravity so basically the higher we get, the lower the speed of sound will be with all other factos being equal.

OR AT LEAST I THINK ;) This one's kinda like the saturday night live skit "deep thoughts"
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#10
04-23-2008, 11:38 PM
 Gold Member Join Date: Dec 2001 Location: Southwest Desert Posts: 721
I'll take a crack at it, it would be about the same at both elevations.
Guess I was a little slow on figuring it out, britz beat me to it.

Last edited by WAMBO; 04-23-2008 at 11:41 PM..
#11
04-25-2008, 04:27 PM
 Platinum Member Join Date: Sep 2004 Location: on the rifle range in Utah Posts: 2,723
Well, actually it was a trick question because there is debate among scientist on this very subject. Some literature says there will be no difference between the two elevations because the sound waves are solely influenced by temp alone. But then there is another side that says gases under varying pressures will also contribute to the sum of the velocity in addition to the temperature. But for the purposes of trajectories, the difference in pressure is so minute that it wouldn't show up on any ballistic program that I know of.
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#12
04-26-2008, 09:35 AM
 Platinum Member Join Date: Mar 2007 Location: MN Posts: 1,218
Quote:
 Originally Posted by goodgrouper Well, actually it was a trick question because there is debate among scientist on this very subject. Some literature says there will be no difference between the two elevations because the sound waves are solely influenced by temp alone. But then there is another side that says gases under varying pressures will also contribute to the sum of the velocity in addition to the temperature. But for the purposes of trajectories, the difference in pressure is so minute that it wouldn't show up on any ballistic program that I know of.
Sound has to have matter to travel through. The more dense the matter is, the quicker the sound will "jump" from molocule to molocule. That is why sound travels very quickly and reliably through water for Sonar to work so well for submarine navigation. That is also why you can put your ear to a railroad rail and hear a train from many miles away. This is very interesting since higher temp is caused by compacted molocules as well. Compacted molocules will transmit sound faster. Space is very cold because there is nothing to heat in a vaccume.

I started to type my response to argue with you, but after thinking it through again I can see your side with this one ;)
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#13
04-26-2008, 10:45 AM
 Gold Member Join Date: Mar 2008 Location: N. Central Indiana Posts: 539
The knowledge base of the members here never ceases to amaze me. Maybe that's why I like this place over others that I've participated in.
#14
04-26-2008, 11:43 PM
 Bronze Member Join Date: Jun 2007 Location: Wyoming Posts: 38
"A bullet fired at double the normal speed will encounter double the air resistance." My understanding was squared resistance when doubling speed, but my memory isn't as good as it used to be. I forgot which law it was as well.

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