Where Does Friction Come From?

Mark Robbins
Johns Hopkins University

Hardly anything is more important in designing mechanical systems than friction. Not surprisingly, the study of friction and use of lubricants
dates back as far as recorded history. The "laws" for static and dynamic friction we teach today date from empirical relationships observed by da Vinci and Amontons centuries ago. However, the microscopic origins of these laws has remained a mystery. New experimental techniques and computer simulations allow us to measure and visualize the molecular interactions and motions that give rise to friction. They also reveal some counterintuitive behavior at the molecular scale. For example, solids may slide over each other with less friction than fluids, and fluid films may behave like solids. These studies are beginning to answer the question of where friction comes from. In particular, we show that the presence of adsorbed surface films and other "third bodies" between two surfaces naturally explains Amontons' 300 year old laws of friction and many other experimental observations.

©Copyright 1999 KSU Department of Physics