Pneumatics Think back to that balloon you blew up and let go. You used your lungs to blow inside it. Each breath you forced inside inflated the balloon a little bit more, pushing outward with some force against the (大气压力) and the stretchiness (elasticity) of the rubber pushing in from outside. So, in physics terms, you used a force (your breath) over a distance (the amount you inflated the balloon): you did what scientists call (功) on the balloon. You compressed the air and forced it into the balloon under pressure. Now (提示:动名词形式) a gas stores energy in it. It takes energy to do the work that squeezes a gas, and the energy you use isn't wasted—it's stored in the (压缩气体) as potential energy you can use later. In other words, inflating a balloon is a bit like filling up a small energy tank (or reservoir) made of rubber. When you let go of the balloon, the trapped gas is released: it expands, so its stored potential rapidly turns back to kinetic energy, making a jet of air that powers the balloon round the room—a very simple kind of .