SCIENCE AT THE EDGE SEMINAR

                     Friday, November 9, 2001
          11:30 a.m., Room 224 Physics-Astronomy Building
                (Refreshments served at 11:15 a.m.)

                  "Where Does Friction Come From?"
              Mark Robbins, Johns Hopkins University

Abstract:

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.