The authors present two geometric descriptions of the frictional properties of a rigid body sliding on a planar surface. The limit surface 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 function is the frictional moment as a function of the instantaneous center of rotation's location. Both of these descriptions implicitly contain the full relationship between slip motion and frictional load for an object that makes contact governed by a useful class of friction laws that 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.>