La fuerza de fricción o la fuerza de rozamiento es la fuerza que existe entre dos superficies en contacto, que se opone al movimiento relativo entre ambas superficies (fuerza de fricción dinámica) o a la fuerza que se opone al inicio del deslizamiento (fuerza de fricción estática). Se genera debido a las imperfecciones, mayormente microscópicas, entre las superficies en contacto. Estas imperfecciones hacen que la fuerza perpendicular R entre ambas superficies no lo sea perfectamente, sino que forme un ángulo con la normal N (el ángulo de rozamiento). Por tanto, la fuerza resultante se compone de la fuerza normal N (perpendicular a las superficies en contacto) y de la fuerza de rozamiento F, paralela a las superficies en contacto.

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Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: \n* Dry friction resists relative lateral motion of two solid surfaces in contact. Dry friction is subdivided into static friction ("stiction") between non-moving surfaces, and kinetic friction between moving surfaces. \n* Fluid friction describes the friction between layers of a viscous fluid that are moving relative to each other. \n* Lubricated friction is a case of fluid friction where a lubricant fluid separates two solid surfaces. \n* Skin friction is a component of drag, the force resisting the motion of a fluid across the surface of a body. \n* Internal friction is the force resisting motion between the elements making up a solid material while it undergoes deformation. When surfaces in contact move relative to each other, the friction between the two surfaces converts kinetic energy into thermal energy (that is, it converts work to heat). This property can have dramatic consequences, as illustrated by the use of friction created by rubbing pieces of wood together to start a fire. Kinetic energy is converted to thermal energy whenever motion with friction occurs, for example when a viscous fluid is stirred. Another important consequence of many types of friction can be wear, which may lead to performance degradation and/or damage to components. Friction is a component of the science of tribology. Friction is not itself a fundamental force. Dry friction arises from a combination of inter-surface adhesion, surface roughness, surface deformation, and surface contamination. The complexity of these interactions makes the calculation of friction from first principles impractical and necessitates the use of empirical methods for analysis and the development of theory. Friction is a non-conservative force - work done against friction is path dependent. In the presence of friction, some energy is always lost in the form of heat. Thus mechanical energy is not conserved.

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