Classroom Balloon Rocket Race

When you blow air into a balloon, you're doing work. You're forcing air into a stretchy, elastic container that really wants to spring back to its original shape. All that pent-up pressure is stored as potential energy: energy that exists but isn't moving yet.

The moment you let go, that potential energy converts instantly into kinetic energy, the energy of motion. Air rushes out of the open end of the balloon in one direction, and by Newton's Third Law of Motion, the balloon shoots forward in the equal and opposite direction.

That's the same basic principle that powers real rockets: exhaust blasts out the back, and the rocket surges forward. As the balloon travels along the string, it gradually runs out of air and slows down, a reminder that the balloon can only release as much energy as was stored inside it.

Friction between the straw and the string also plays a role, adding resistance that eventually brings the rocket to a stop. The tighter the string, the less friction, and the farther your balloon rocket will fly.

Pro tip: Want to race? Set up two parallel tracks side by side and have two students launch at the same time. Try varying the amount of air in each balloon to see how it affects speed and distance — that's Newton's Third Law in action.