1. The problem statement, all variables and given/known data I am doing a project where I will be using a pressurized PVC pipe to lob a beanbag over a barrier and onto a ground target. Like a potato cannon, 1 chamber will have ~ 6.5 atm absolute pressure and when a valve is released, gas will flow along the pressure gradient into a second chamber holding the beanbag. I am having trouble describing the system's energy state when the PVC pipe is at 6.5 atm just prior to launch. 3. The attempt at a solution At t = 0 just prior to launch, the beanbag has no kinetic energy and has a small amount of gravitational potential energy. Is there a way to describe the compressed gas in the lower pipe as a potential energy source? I know I could do that if there was a compressed spring under the beanbag, so I am wondering if compressed gas can similarly be considered a potential energy source. I'm very rusty on my basic physics and the only other way I can think of describing the state at t = 0 is to calculate the velocity of the compressed gas as it moves along the pressure gradient, and treat it like a collision when it contacts the beanbag. Any hints or pointers would be greatly appreciated!