Static, kinetic, and stick-slip friction

In technical applications, stick-slip friction is detrimental in terms of wear, vibrations, and precision of movement. Stick-slip  

To avoid stick-slip, one should try to make the spring constant high enough (using stiff materials and stable constructions). It can be shown, that stick-slip may also arise from the velocity dependence of the friction coefficient [460], When the friction coefficient decreases with sliding velocity, stick-slip is amplified. When the friction coefficient increases with velocity, stick-slip is damped out. The former is usually the case at low speeds, certainly for the transition from static to dynamic friction, whereas the latter prevails usually at high velocity. 

Important examples of stick-slip are earthquakes that have long been recognized as resulting from a stick-slip frictional instability. The use of a full constitutive law of rock friction that takes into account the time dependence of /is and the dependence of /j k on speed and sliding distance can account for the rich variety of earthquake phenomena as seismogenesis and seismic coupling, pre- and post-seismic phenomena, and the insensitivity of earthquakes to stress transients [461], 

Macroscopic stick-slip motion described above applies to the center of mass movement of the bodies. However, even in situations where the movement of the overall mass is smooth and steady, there may occur local, microscopic stick-slip. This involves the movement of single atoms, molecular groups, or asperities. In fact, such stick-slip events form the basis of microscopic models of friction and are the explanation why the friction force is largely independent of speed (see Section 11.1.9). 

The simple concept of constant static and dynamic coefficients of friction does not assume anything on how the transition from stick to slip occurs. The transition from sticking to sliding between two transparent PMMA blocks was studied experimentally in detail by Rubinstein et al. [928] who found that the onset of friction is connected to the propagation of crack wave fronts, which lead to a rupture of the interface. 

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