<P> Rubbing dissimilar materials against one another can cause a build - up of electrostatic charge, which can be hazardous if flammable gases or vapours are present . When the static build - up discharges, explosions can be caused by ignition of the flammable mixture . </P> <P> Belt friction is a physical property observed from the forces acting on a belt wrapped around a pulley, when one end is being pulled . The resulting tension, which acts on both ends of the belt, can be modeled by the belt friction equation . </P> <P> In practice, the theoretical tension acting on the belt or rope calculated by the belt friction equation can be compared to the maximum tension the belt can support . This helps a designer of such a rig to know how many times the belt or rope must be wrapped around the pulley to prevent it from slipping . Mountain climbers and sailing crews demonstrate a standard knowledge of belt friction when accomplishing basic tasks . </P> <P> Devices such as wheels, ball bearings, roller bearings, and air cushion or other types of fluid bearings can change sliding friction into a much smaller type of rolling friction . </P>

How many different types of friction are there