39is the resistance that occurs when a round object such as a ball or tire rolls on a flat surface. It is caused by the deformation of the object, the deformation of the surface, or both. Additional contributing sources include surface adhesion and relative micro-sliding between the surface of contact. It depends very much on the material of the wheel or tire and the sort of ground. Additional factors include wheel radius, and forward speed.[1]
For example, rubber will give a bigger rolling resistance than steel. Also, sand on the ground will give more rolling resistance than concrete. A vehicle rolling will gradually slow down due to rolling resistance, but a train with steel wheels running on steel rails will roll much farther than a car or truck with rubber tires running on pavement. The coefficient of rolling resistance is generally much smaller for tires or balls than the coefficient of sliding friction.[2]
The primary cause of rolling resistance is hysteresis:
A characteristic of a deformable material such that the energy of deformation is greater than the energy of recovery. The rubber compound in a tire exhibits hysteresis. As the tire rotates under the weight of the vehicle, it experiences repeated cycles of deformation and recovery, and it dissipates the hysteresis energy loss as heat. Hysteresis is the main cause of energy loss associated with rolling resistance and is attributed to the viscoelastic characteristics of the rubber.
