ABSTRACT
Friction is a remarkable phenomenon. As pervasive as friction is in daily experience, there is still much to learn about its nature, how it changes under different circumstances, and how it can be predicted and controlled. Its effects on the behavior of machines and materials have been the source of study and contemplation for hundreds and even thousands of years, reaching back at least as far as Aristotle (384-322 BC).1 In fact, it could be argued that the undocumented rst use of a log or rounded rock to move a heavy object was an engineering solution to a prehistoric friction problem.
