My physics teacher is saying that: The friction force acting on a wheel that is spinning is = to the STATIC friction force of the rubber wheel material on the cement. That doesn't make any sense though because the static friction force is greater than the kinetic friction force so based on what he is saying it would be easier to slide the wheel across the ground sideways than roll it. The whole point of a wheel is to reduce friction isn't it?! Am I missing something here? Im not argueing that there are no static friction forces involved but it would not be the same force(mu) as a block of rubber laying on a cement block. I know rubber on cement isn't very accurate because they are not completely smooth surfaces. Yes but even so when you are trying roll a tire you are not trying to start the rubber sliding across the cement(where static friction force would come into play) you are simply trying to get it to roll. Yes there will be some friction acting between the rubber and the cement but it won't be the same as if you tried to start sliding it across the cement.