Limit surface and moment function descriptions of planar sliding

We present two geometric descriptions of the frictional properties of a rigid body sliding on a planar surface. The limit surface LS, from classical plasticity theory, is the boundary of the set of all possible frictional forces and moments that can be sustained by the frictional interface. Zhukovskii’s moment finction is the frictional moment as a function of the instantaneous center of rotation’s location. Both of these descriptions implicitly contain the full rela tion between slip motion and frictional load for an object which makes contact governed by a useful class of friction laws which includes Coulomb friction. These surfaces can be used to deduce results concerning the overall frictional motion behavior of rigid bodies such as the existence of characteristic final slip motion directions.