Friction is a necessary evil. Without friction, we cannot walk, hold articles, the brakes of automobiles do not work, and the power of a motor cannot be transferred to a grinding machine.
However, friction is undesirable in certain areas and we need to reduce it. Friction between the sliding surfaces of two objects can be reduced by making the surfaces in contact smooth by polishing the surfaces. Sliding friction between the moving parts of vehicles can be reduced by using oil, grease or graphite. In electrical plugs, graphite is used to reduce friction between the plug pins and the corresponding socket. In certain machines, like the drill used by a dentist, a layer of air is used as a lubricant to reduce friction between the moving parts.