1. Fluid Film or Thick film or Hydrodynamic lubrication:

• In this lubrication, the lubricant chosen should have the minimum viscosity under working condition & at the same time it should remain in place and separate the surfaces. In such system friction is independent of the load, but depends on the viscosity, thickness of film & relative velocity and area of surfaces.
• The Co-efficient of friction in such a case is as low as 0.001 to 0.03. This type of lubrication is used in delicate instruments and light machines like watches, clocks, guns, etc.
• Hydrocarbon oils are considered to the satisfactory lubricants for fluid-film lubrication. In order to maintain suitable viscosity of the oil in all season of a yare, ordinary hydrocarbon lubricants are blended with selected long chain polymers.