Rolling resistance

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Rolling resistance is the component of normal force between two surfaces in contact that, due to microscopic surface deformations, acts in the direction along the tangent plane to the point of contact, in a direction that opposes the motion of the two bodies against each other.

Rolling resistance occurs both when two bodies are sliding against each other and in the case of pure rolling of one body (a cylinder or sphere) against the other (a flat surface). However, in the case of sliding or slipping motion, rolling resistance is negligible compared to kinetic friction, and can be ignored. In the case of rolling, since kinetic friction does not act and static friction does not oppose the rolling tendency, rolling resistance becomes the primary force that opposes the rolling tendency and eventually brings the rolling to a halt.

The magnitude of rolling resistance depends on the nature of the surfaces in contact and the magnitude of the normal force. The constant of proportionality C_{RR} such that the rolling resistance is C_{RR} times the normal force is termed the rolling resistance coefficient, and its magnitude is generally less than 0.01.