Brakes increase the amount of friction on the wheel, allowing the rider to slow or stop.
A person can use the brakes by pulling on levers which pull cables, forcing pads against the inner rim of the wheel. These pads cause a retarding force on the rim of the wheel, in the opposite direction that the wheel is turning. There is one lever on each handle bar, and each lever controls either the front or rear wheel. When bicycling, a person must be careful when applying the brakes, because his body has inertia and it still tends to go forward. This shifts his weight forward onto the front wheel.