What is Friction? A brief and biased primer

Friction is an ubiquitous phenomenon we encounter every day. A mundane effect at first glance, the term friction covers a surprising wide variety of micro- and macroscopic phenomena, including such exotic members as friction between single molecules or ani- sotropic friction within biopolymers. Moreover, the reduction of friction and associated wear is of large importance in a wide range of technological applications.

In this lecture, I will detail on the origin of a selected set of friction types, and outline how to calculate quantitative parameters describing friction. Furthermore, I will discuss how friction emerges in many-body dynamics as well as its relation to fluctuations. Last, I will demonstrate that friction is not necessarily a nuisance, but can become a key to tech- nical applications, e.g., in friction welding or rocket science.