Air molecules stuck inside an inflated balloon collide continuously with the inner surface of the balloon. Each collision provides a little push outward on the balloon. All the many collisions working together keep the balloon inflated. To get a “feel” for what’s happening here, add about a tablespoon of tiny beads to a large balloon (pellets, beans, BBs, or grains of rice also work). Inflate the balloon to its full size and tie it shut. Hold the balloon in the palms of both hands and shake rapidly. Can you feel the collisions? As you shake the balloon wildly, the flying beads represent the gaseous phase. How should you move the balloon so that the beads represent the liquid phase? The solid phase?