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Posted:

May 1, 2009

Bio:I do parkour. It's an obsession. The philosophy that follows is amazing. It's my religion almost! Whenever I'm resting, I'll either be in school or drafting a new project. I never really watch TV or p...read more »

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active| newest | oldestimpact, thats a totally different thing. :)Pressure= force / area

Force = mass * acceleration

Once you have a few missing variables, then it gets more complicated, friction, wind resistance, etc. You can read up more on it. Good luck.

_{Close, and helpful information, but I need to find the FPS of a certain projectile's mass with a certain PSI/force that is in a certain diameter of piping. Get it?}-PKT

F=MA orA=F/MAs an example 50 PSI on a 1" surface gives a

Force of 50Lb. If the projectile is 1/16Lb yourAcceleration is 50*16 (Diameter of pipe will give area through pi*r^{2})Final velocity = root(2

A*length of pipe travelled)L

Acceleration is the

rateat which speed changes, i.e. how fast it goes from zero to final muzzle velocity. SI is meters per second per second (ms^{-2})M is Mass (SI Kg)

The last is an equation of motion

L

Pounds perSquareInch, the amount of push (Force) depends upon how many square inches the compressed air is pushing against.If you think of your tube, and a simple projectile (like a wine-cork) the air pushes on the end of the cork, in this case a circle about

^{3}/_{4}of an inch across. The area of the circle (several burning questions Instructables on this) is given by pi x r^{2}which as an approximation is 3.1416 x (^{3}/_{8}x^{3}/_{8}) is about 0.44 square inches. "r" is the radius which is half the diameter (^{3}/_{4}inch)Multiply the PSI by the area calculated above and you have the force in pounds acting upon the projectile.

The force will cause the projectile to Accelerate, which can be quantified as the Force you calculate above divided by the mass of the projectile. More force = more acceleration, more mass means less.

The equation of motion is derived elsewhere (previous link), the speed at which the projectile leaves the tube is given by the square root (don't have symbol) of (2 x Accelleration x the length of pipe that the projectile travels)

Condensed:

Speed = sq root ( (2 x length of pipe x PSI x pi x r^{2}) / mass)(I think)

I'm probably not going to be able to do a better job than that, it's a bit tricky. But as I said earlier, experimental measurements may be better in real terms.

L

exactlywhat I was looking for!