The Nature of Static and Kinetic Friction

The introduction to the concept of static and kinetic friction in Chapter 7, Section 2 is admittedly simplistic. Familiarity with the experimental details of measuring friction leads to a more realistic view in behavioristic terms and also to some theoretical questions. In particular, the theory of stick-slip friction requires that be greater than and distinct from and indeed Fig. 7-5a shows a discontinuity between static and kinetic friction. But the model for the fundamental adhesive mechanism of friction does not predict such a discontinuity. 

Displacements corresponding to sliding in the macroscopic sense are outside the range of the apparatus. 

VI instead, allowing for the irregular character of the sustained slid- 

The factor that is least controllable in the deduction of static and kinetic friction values from stick-slip experiments is the condition of the contacting surfaces. This explains why Brockley and Davis [20] in their study of the influence of the time of contact on were unable to obtain repeatable results, as shown in Fig. 8-15a. For each series of determinations made with a single placement of the rider on the track, the plot of against the time of quiescent contact shows satisfactory self-consistency. But when the experiment is repeated with a fresh placement of the rider on the track, a different curve is obtained, self-consistent but not a duplicate of the previous experiment. This was traced to the variability of the surface with location on the rubbing track. Furthermore, it was demonstrated that a model of time-dependent junction growth could be made to yield the following expression  

Kato ei at. [21] found that the value of the coefficient of static friction depended on the duration of the stick portion of the cycle in lubricated stick-slip sliding of cast iron on cast iron according to the formula 

---