A sprocket is a wheel with teeth around its edge that fits into the links of a chain, making the chain move when the wheel turns. If you flip your bicycle upside down and look at the gears near the pedals or back wheel, you're looking at sprockets. When you pedal, the front sprocket turns, pulling the chain, which then turns the rear sprocket and makes the wheels spin.

Sprockets are simple but crucial inventions. They appear in bicycles, motorcycles, conveyor belts in factories, and even old film projectors. The teeth on a sprocket catch onto the chain links, so nothing slips. Without sprockets, we couldn't efficiently transfer rotating power from one place to another.

The size of a sprocket matters too. On a bike, switching to a larger front sprocket or smaller rear sprocket makes pedaling harder but lets you go faster, like shifting into a higher gear. Mechanics and engineers carefully choose sprocket sizes to get exactly the speed and power they need for different jobs.