No expert here, my physics is plenty rusty but here is what I was taught;
F=MA
Acceleration has to be taken into account as does mass in computing force. How to measure the acceleration on the case escapes me. In theory, Newton's third law tells us the rearward force on the rifle is equal to the forward force acting on the projectile. Much of that, however, is acting on the mass of the rifle as a whole. What is the fraction acting on the case head? My instincts tell me it's irrelivent. Measuring pressure empirically factors everyting into account. All that's needed to understand the implications is the area of the case head.
A better question might be, what is pressure? For our purposes it is determined through experimentation with sensors. Most of us can understand crusher testing devices. It doesnt matter how fast or how slow- the copper crusher cylinder will be deformed a certain amount. You can deform it slow with a hydrolic press or fast with a hammer; if it's deformed the same amount, the "pressure" is equal.
I think the bottom line is we are confusing two different vectors. Force might best be visualized as the anvil dropped from ten feet high which hits a bridge- which would normally support it's weight- and crashes through. The acceleration of gravity over distance has acted on the anvil's mass, increasing the force.
Pressure is the amount the anvil deforms whatever it hits; like the copper crusher, it's acceleration is already taken into account.
Is there a engineer/physics professor in the house?
Best,
C.
Last edited by C. Kofoed; 02/28/09 10:05 PM.
