The most common methods used to reduce friction between moving surfaces include polishing the surfaces that come into contact, lubricating the surfaces, using ball or roller bearings and streamlining. Friction is defined as the force that resists one surface from sliding or rolling against another surface. This means that friction is only present when one or both of the surfaces that are in contact are in motion.
Several factors affect the force of friction generated, also called the friction coefficient, between surfaces. These factors include the surface finish, temperature, operational load, lubricant characteristics and the nature of the relative motion between the surfaces.
Polishing the surfaces will smooth out the irregularities and the roughness between the surfaces, which in turn will reduce the coefficient of friction that the surfaces will generate. Lubrication provides a thin layer of liquid between two surfaces, which fills up the small gaps and irregularities on the surfaces, thus lessening the coefficient of friction.
The use of ball bearings and rollers greatly reduces friction between surfaces, as it changes the nature of the relative motion between the surfaces from sliding to rolling. Streamlining applies to the friction generated by the wind and liquids. By adopting a more streamlined shape, the flow of air or liquid will be smoother and easier against the surface of a particular object.