Bicycles are easy to understand. Modern bikes have only about 1,500 parts!
In the last century or so, gears and hand-operated brakes have made bikes much better. But the basic bicycle design hasn’t changed a lot since the 1880s. Every bike has a foot-powered cog-and-chain system (the rear cog is also called the sprocket). The chain moves energy from the pedals to the back wheel. This is what makes bicycles the most efficient human-powered transportation. It’s more efficient than walking and running, or even riding scooters and skateboards.
