coefficient of friction

The coefficient of friction is a number characterizing the force necessary to slide or roll one material along the surface of another. If Fs = the frictional resistance when a body is on the point of sliding along a specified surface, Fk = the frictional resistance when steady sliding has been attained, and R = the perpendicular force between the surfaces in contact, the static coefficient of friction = Fs/R; the kinetic friction = Fk/R.