ABSTRACT
Friction force is proportional to the normal load as stated by Amontons-Coulomb’s law. For microloads less than 1 mN, which are often found in mechanisms such as microelectromechanical systems (MEMS), Amontons-Coulomb’s law is not valid due to the effect of the adhesion force between the contacting surfaces [1]. Studies show that, at such microloads, either the attraction force (adhesion force) caused by the surface tension of water condensed on the surface or the van der Waals force dominates the friction force, and that the friction force is proportional to the sum of the adhesion force (pull-off force) and the normal load [2, 3].
