How do pedals turn a wheel?

Have you ever ridden a bike, or watched someone ride one? Maybe you felt the wind on your cheeks. Your feet go round and round, and the bike rolls along.

Your feet only touch the pedals. They never touch the wheels at all. So how do pedals turn a wheel? Let's look closely and find out.

Each pedal sits on the end of a short metal arm. This arm is a crank, which means the bar that swings the pedal round. When your foot pushes the pedal down, the crank swings round in a circle.

In the middle of the bike, the two cranks join together and hold on to a big round plate. This plate is a gear, which means a round piece with little teeth all around its edge. When the cranks swing, the gear turns round with them.

A long metal chain loops around the gear. The gear's teeth poke into little gaps in the chain. As the gear turns, its teeth grab the chain and pull it along. The chain stretches all the way back, so what do you think it pulls on next?

Back by the rear wheel, the chain loops around a second gear. This one is small. The chain tugs on its teeth, so the small gear spins too.

That small gear sits tight in the middle of the back wheel. When the small gear spins, the back wheel has to spin with it. Whoosh, the wheel turns!

Crank, gear. Your feet turn the cranks, and the gear pulls the chain that turns the wheel.

Sweet dreams, little rider, and may your next bike ride roll along happily.