Static friction phenomenology

Kinetic friction differs phenomenologically from static friction in that rather than being in a state of impending or beginning motion, the sliding body is moving overtly with respect to the stationary body. Me write the following expression for the coefficient of kinetic friction... 

N (7-6) where is the negative of the tangential force required to keep the slider moving at constant velocity. Equation 7-6 is a formal statement defining the coefficient of kinetic friction and also the expression of a phenomenological fact. Its counterpart for the coefficient of static friction is... 

In terms of the behavior that actually would be observed with a simple apparatus of the kind described above, there is a direct and obvious phenomenological difference between static and kinetic friction. Close inquiry has revealed that in addition to theoretical considerations, the experimental methods and the instrumentation used to study and measure friction are an important aspect of the behavioristic manifestation of this difference. Therefore an examination of some-7 of the more refined methods for the investigation of friction is in order. 

---