AP Physics 1

A Rolling Hoop

What type of friction is present in a rolling wheel?

In the below video and still pictures you will see a rolling hoop that has been marked on the edge. Notice that the marks on the bottom of the hoop are in focus, while the marks on the top are blurry. This tells us that the hoop is momentarily at rest at the bottom while the rest of the hoop pivots aroung that point. Thus we see that it is static friction that is at work here, which is why anti-lock brakes work that way that they do. The brakes are always trying to keep the rolling tire in the realm of static friction which is much greater than kinetic friction. 

Still Pictures of the same Rolling Hoop

Photo 1 of rolling Hoop

Photo 2 of rolling Hoop