Friction

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Friction is both a name for the counter-force, the physical deformation and the heat buildup that occurs when two surfaces travel along each other whilst forced together.

The friction-force is a function of the force pressing the surfaces together and the friction coefficient of the material interface. The initial force needed to start movement is generally higher than the force needed to sustain a movement.

Physical deformation is a consequence of friction-force. Whereas this can be beneficial, as in polishing, it is often a problem, as the materials are worn away, and no longer holds the specified tolerances.

Heat buildup is yet a consequence of the energy invested in movement under friction. The work of movement will translate into deformation and heat that in the long run may affect the materials specification, and indeed the friction coefficient. Friction can become so intense that solid materials melt and assume liquid form.

Friction may occur between solids, gases and fluids or any combination thereof, see aerodynamics and hydrodynamics. Also, friction occurs inside deforming objects.

A common way to reduce friction is by using lubricant that is placed between the two surfaces, often radically lessening the percentage of the work that is turned into heat, which is the coefficient of friction.