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