Author's Homepage:   Kurt M. Marshek
Chapter 18: Clutches and Brakes
"With the sliding surfaces encountered in most machine components - in bearings, gears, cams, and many others - it is desirable to minimize interface friction in order to reduce energy loss and wear. In contrast, clutches and brakes depend on friction in order to function. With these members, one objective is to maximize the friction coefficient, and keep it uniform over a wide range of operating conditions, and at the same time to minimize wear."