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Joint Friction and Lubrication

Discussion

(see also synovial fluid)

  • coefficient of friction for two surfaces can be thought of as degree of roughness that exists between two surfaces;
  • where as solid friction is relatively independent of velocity of motion, fluid friction forces are sensitive to velocity & to lubricant film thickness;
  • increase in joint velocity is not accompanied by an increase in joint friction;

effects of strain rates

  • at low strain rates, synovial fluid behaves as a viscous fluid;
  • at high strain rates, the hyaluronic molecules becomes entangled which causes them to behave more like an elastic solid;

3 basic modes of lubrication

  • fluid film;
    • occurs when the two surfaces are separated by a layer of fluid so that opposing surfaces do not contact each other;
    • friction is governed by fluid hydrodynamics (like a car hydroplanning on a wet road);
  • boundary layer
  • mixed

Additional Information