Lubrication

Lubrication reduces friction between contacting surfaces through naturally produced or externally supplied substances. It can also limit wear and heat generation.

Boundary lubrication: A lubrication regime in which adsorbed molecules or surface films reduce friction while much of the load remains supported by surface contact. This regime operates when a full fluid film cannot separate the contacting surfaces.
Friction: Resistance to relative motion between surfaces in contact. Lubrication reduces this resistance at interacting surfaces.
Joint lubrication: The processes that reduce friction between tissues within movable joints. It is the biological form of lubrication described here.
Dry friction: Friction between surfaces without an intentionally supplied lubricant film. It contrasts with friction reduction through a lubricant.
Hydrodynamic lubrication: A regime in which motion draws viscous fluid into a converging gap, creating pressure that separates surfaces. It shows how relative motion can generate a load-bearing lubricant film.
Wear: The progressive loss or deformation of material caused by contact and relative motion. Lubrication often reduces the surface damage associated with friction.
Tribology: The study of friction, wear, and lubrication between interacting surfaces. It provides the engineering framework for analyzing lubrication.
Adhesion: The attraction between unlike surfaces or materials in contact. Lubrication can reduce adhesive interactions that contribute to friction and wear.
Elastohydrodynamic lubrication: A lubrication regime in which high pressure deforms surfaces and increases lubricant viscosity within a thin film. It describes film formation at highly loaded, curved contacts such as gears and joints.
Synovial fluid: A viscous fluid within synovial joints that lubricates cartilage and supports joint function. It is the principal natural lubricant in freely movable joints.

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