How do engines work?

Pop open the hood of a car and you'll see a lump of metal the size of a small suitcase, bolted down and wrapped in hoses. It just sits there. But when you turn the key, that lump wakes up and starts exploding — thousands of tiny, controlled explosions every minute — and those explosions are what push the car down the road.
An engine is a machine that turns fuel into motion. The fuel — usually gasoline — is a liquid packed with energy, like a bottle of lightning. The engine's job is to unlock that energy and use it to spin a shaft, which eventually turns the wheels. The trick is doing it in a way that's powerful, smooth, and doesn't blow the whole car apart.
