
21Introduction
observations about friction force and equations to calculate such force.
Despite that, for centuries friction remained an ad hoc force that was intro-
duced to solve various problems. Unlike the rest of the entire building of
the science of mechanics, it was not embedded into the texture of mechani-
cal concepts or deduced from any fundamental principle. Furthermore, the
very compatibility of friction with the rest of mechanics was questionable
due to the existence of so-called paradoxes (logical contradictions) discov-
ered in the 1890s by French mathematician (and prime minister of the Third
Republic!) Paul Painlevé (1863–1933