ABSTRACT

Friction, the resistance to relative motion between a solid body and another solid body or substance, is so common an everyday experience that it has been the source of philosophical contemplation and experimental investigation throughout history. Friction broadly encompasses not only ¨uid friction in pipes, aerodynamic friction, and the friction between dry or wet sliding surfaces in mechanical parts like seals, brakes, bearings, gears, but also friction in natural phenomena, ranging from human joints to tectonic plates. Because friction takes so many forms, no universal, overarching theory or model successfully explains it.