Thread: Cheap chrono
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Old August 6th, 2006, 13:20   #11
Luckyorwhat's Avatar
Join Date: Aug 2005
Location: calgar
Originally Posted by Shotgun-MAn
you don't need 2 mics, one will work fine, just mesure your shooting distance, and the amount of time between the sound of the gun firing, and the sound of the projectile hitting your target and do some math, and you then have your average velocity for that shooting range, but you won't have the actual muzzle velocity.

If you want to be really precise you would have to factor in the placement of your microphone, and the speed of sound at your locations altitude.
You know what's wierd? I've always understood that sound is faster at higher altitudes, too. Because that's why skydiver's couldn't break the sound barrier, not even NASA guys testing high-altitude ejections, because they'd fall fast being in the thin air, but sound was even faster because of the thin air.

But I checked Wikipedia just now to confirm, and it says altitude has no effect on Vsound, per se. Pressure and density are irrelevant, all that matters is temperature (which will be lower higher up).

Anyone else heard this, or have independent confirmation, Wiki is good, but not infallible.
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