The maximum force of static friction fsM between any pair of dry unlubricated surface follows these two empirical laws (1)It is approximately independent of the area of contact surfaces 2)It is proportional to the normal force s Max (57) Where N the magnitude of the normal force, us the coefficient of static friction s Max the maximum force of static friction f≤∫ S MaxThe maximum force of static friction between any pair of dry unlubricated surface follows these two empirical laws : (1) It is approximately independent of the area of contact surfaces. (2) It is proportional to the normal force (5-7) where N the magnitude of the normal force, the coefficient of static friction, the maximum force of static friction. s s s Max f N =  sMax f sMax f s sMax f f 