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 |