Static friction fs is a constraint force because it prevents

Last updated: 6/25/2023

Static friction fs is a constraint force because it prevents relative sliding between contacting surfaces It acts tangentially to the surfaces in contact Hence we call it tangential contact force It is a macroscopic effect of intermolecular forces between the molecules of the surface in contact Static friction basically is an interlocking of the microscopic surface irregularities projection When the surfaces tend to slide fs comes into play The tendency of relative sliding is characterised by a relative acceleration in the absence of friction We can find the relative acceleration a12 and a21 of each surface by as usual process by drawing FBD and writing force equations excluding frictional forces between the surfaces under consideration If the surface 1 has acceleration a12 relative to surface 2 static friction s acts on surface 1 in opposite direction of 12 Similarly 52 acts on surface 2 opposite to 21 Thus static friction opposes the tendency of relative sliding for 1 7