Rolling resistance

Rolling resistance, also called rolling friction and rolling drag is a force of resistance that slows down a rolling motion of one body against another. In other words, it is a force that opposes the tendency of one body to roll against each other.

Important facts about rolling friction

• For rolling resistance to operate, it is not necessary that the two bodies be rolling against each other. In fact, rolling resistance operates even when two bodies are sliding against each other. However, this is negligible compared to the (kinetic) friction acting between the bodies, so is usually ignored.
• Rolling friction operates primarily because of deformations at a microscopic level between the surfaces of contact.
• The amount of rolling friction between two bodies depends on a number of complicated factors, including the nature of the surfaces in contact, the normal force between the two surfaces, and the overall geometry of the bodies.

Rubber tires

For inflatable rubber tires (as used for automobiles and bicycles), the amount of rolling resistance is greater for underinflated tires, owing to the greater deformation when the air pressure inside the tire is reduced. Cars and bicycles will experience more rolling resistance on dirt roads or sand than on hard pavement, as there is additional deformation in the underlying surface in addition to that of the tires.