A piston is a solid cylinder that moves up and down inside a tube, converting pressure into motion or motion into pressure. Think of pushing a bicycle pump: the rod you press down is connected to a piston that squeezes air through the tube and into your tire.

In car engines, pistons are the workhorses that make vehicles move. When fuel burns in the engine, it pushes pistons down with tremendous force. The pistons connect to a crankshaft (a rotating shaft), converting that up-and-down motion into the spinning power that turns the wheels. A typical car has four, six, or eight pistons firing in sequence, like a drummer playing a rapid beat. Each piston might move up and down thousands of times per minute.

Pistons appear in many machines beyond cars: steam locomotives, hydraulic lifts, air compressors, and even some brass musical instruments, where piston valves or sliding tubes change the sound. The piston is one of the most important inventions in mechanical engineering. For centuries, pistons have been turning various kinds of energy into useful motion, powering everything from factory equipment to spacecraft life support systems.