When a wheel rolls along the ground, friction causes the wheel to rotate and prevents it from sliding along the ground. This rolling friction is a combination of static and kinetic friction, caused by surface roughness and a molecular attraction between the materials. This lesson will try to answer those questions. There is a mini-quiz at the end of the lesson. Suppose you started a wheel rolling by giving it a push near the top of the wheel.
Static friction holds the bottom of the wheel, causing it to start rolling.
This action is similar to trying to tip over a rectangular block. The static friction holds the bottom until the block tips or the wheel rolls. Once wheel starts rolling, friction will slow it down. Automobiles and bicycles move forward by applying a torque to an axle on the wheel. If the torque is greater than the friction force, the wheel will slip or spin.