It was recalled that, when reasoning in solid-state physics had been purely phenomenological, it had been usual to distinguish only so-called viscous or solid friction, in which the resistance to motion had been assumed to be proportional to the velocity, or independent of the velocity, respectively. It was stressed here, on the basis of specific examples, that such descriptions were insufficient when applied to the motion of lattice defects at the atomic scale.

Viscous and Solid Friction in the Motion of Crystal Defects. J.Friedel: Czechoslovak Journal of Physics, 1995, 45[11], 907-12