In the field of friction, pull-off force (rupture or unbinding force) required to break a bond has been thought to be independent of the necessary time, which is termed the bond lifetime, to dissociate the bond. However, the author presents here that friction forces are equal to pull-off forces and that they are revealed as an exponential function of the bond lifetime through rupture dynamics. The result of rupture dynamics that expresses essentially stochastic behavior was employed here as a tool to connect the atomic friction theory of Tomlinson and a modified adhesion model of Israelachvili that was first developed by Bowden and Tabor.