How much energy is stored in a evacuated tube? So in this video they have an evacuated tube with a golfball at one end, they quickly open one end and the golf ball shoots out the other, hitting a target. Resulting in a rapid unplanned disassembly of the golf ball.
This got me wondering how much energy is 'stored' in an evacuated tube; and how you would calculate it?
 A: No energy is stored in the tube, but a lot of energy is stored in the atmosphere.
Consider a piston at the end of an evacuated tube. Across this piston, there is a pressure differential $p$ equal to exactly 1atm (assuming a perfect vacuum). Multiply this pressure by the area $A$ of the piston, and you get a force working on the piston.
Work is defined as the integral of force over displacement. If we slowly (quasi-statically) move the piston, we can note that the pressure $p$ across the piston never changes, so the force is constant over time. Thus, we can simply say that the total work is simply the force multiplied by the displacement, i.e., the length $l$ of the tube. The maximum amount of work that the atmosphere can perform on the piston is then $$W = pAl$$
For most practical points and purposes, one could say that the maximum work that the atmosphere can do on the piston is the 'energy stored in the vacuum'. We can safely replace the piston by the golf ball and not change the physics much. Note that the 'energy stored in the vacuum' will not be equal to the potential energy of the golf ball, because the golf ball cannon cannot be 100% efficient, for the simple reason that air friction makes this an irreversible process.
