Microscopic Friction

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Tribology (from the Greek word “tribos”, which means “to rub”) is the study of friction, lubrication, and wear, an inherently challenging field requiring much interdisciplinary cooperation. By most recent estimates, improved attention to tribology would save developed countries up to 1.6% of their gross national product, or over $100 billion annually in the United States alone. The magnitude of the financial loss associated with friction and wear arises from the fact that entire mechanical systems, be they coffee makers or automobiles, are frequently scrapped when only a few of their parts are badly worn. In the case of an automobile, the cost of the energy consumed in its manufacture is equivalent to that required to operate it for 100,000 miles.

Macroscopic tribological behavior is known to be highly sensitive to the details of interfacial contact at the atomic scale. For example, it is well known that adsorption of molecularly thin coatings on contacting surfaces can reduce their macroscopic friction coefficients by orders of magnitude. Investigations of the origins of such macroscopic tribological behavior should ideally performed at both atomic length scales (10-9 m) and time scales (10-12 to 10-9 s). Such studies, however, have proven to be extremely challenging, as they are performed on buried interfaces that are extremely difficult to experimentally probe.

When an object moves along a surface or through a viscous liquid or gas, the Forces resisting its motion are referred to as friction. Frictional forces are nonconservative, converting the kinetic energy of materials in sliding contact to internal energy

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