or can take the microscopic roughness as the starting point. The latter class of models shall have a greater predictive power, and potentially can be used for a large spectrum of applications. However, because of the strong non-linearity of the contact/friction mechanisms and extreme complexity of surface roughness, construction of a reliable analytical micro-mechanical model presents a serious challenge. Moreover, the scale separation which would allow to separate the macroscopic shape of contacting solids and the accompanying roughness cannot be always ensured.

Admittedly, all the aforementioned phenomena are strongly related to the surface roughness. (1) The compression of contacting asperities as well as their interlocking contributes to the interfacial stiffness. (2) According to the adhesive theory of friction the frictional resistance of contacting spots is pressure independent and thus the total frictional resistance of the interface is proportional to the true contact area. In general, this area may depend on the hold-time or sliding velocity manifesting itself as a velocity-dependent friction coefficient. (3) In case of adhesive wear, the removed volume depends on the characteristics and number of contact spots forming the true contact area. (4) The overall thermal conductivity of the interface is determined by heat (phonons and, if 