Friction and Surface Area

If the equation for the force due to friction does not include surface area, why do drag racers have large tires that make contact with the ground over a large area. This should not give them an advantage since friction would be unrelated to the area in contact with the ground.
- Nick (age 26)
Cincinnati, OH

Good question. The usual rules that we teach about friction forces in beginning classes are just rules of thumb. The sliding friction force between two surfaces does turn out to depend mostly on the normal force between them, not on how much surface area it's spread over. The reasons for this approximate relation are very complicated and were still being actively explored, last I heard. So if under some conditions the rule breaks down, that's not exactly surprising.

Mike W.

(published on 07/26/2013)