# Rolling friction

Rolling friction is defined as the phenomenon of resistance to motion due to the rolling between the surfaces of two material bodies in contact. The resistance produced by rolling friction is, in general, much lower than that generated by sliding friction.

### Laws of the rolling friction of Charles-Augustin de Coulomb

1. law: the rolling friction is proportional to the normal component on the contact surface (for example in the case of horizontal surfaces we have the weight force);
2. law: rolling friction depends on the nature and state of the bodies in contact. This occurs similarly to sliding friction; an example of how this affects the friction force is that it is much easier to drive a car on asphalt than on dirt;
3. law: the rolling friction is inversely proportional to the radius of the rolling body (therefore its width): this is because the greater width of the contact surface causes a lower sinking of the body, as the unit pressure of the weight is lower; besides, the increase in the radius of the body results in an increase in the lever arm and the moment of rotation.
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