Static and dry friction due to multiscale surface roughness.

It is shown on the basis of scaling arguments that a disordered interface between two elastic solids will quite generally exhibit static and dry friction (i.e., kinetic friction which does not vanish as the sliding velocity approaches zero) because of Tomlinson-model instabilities that occur for small-length-scale asperities. This provides a possible explanation for why static and dry friction are virtually always observed, and superlubricity almost never occurs.