Joint Friction and Lubrication


- Discussion: 
    - see 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

 An Introduction to Tribology




Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Friday, June 1, 2012 11:36 am