Asperity deformation plays a fundamental role in wear and friction yet it is largely hidden from view during dynamic contact. The obscurity of asperity deformation impedes understanding the underlying mechanism involved and is a major experimental problem in tribology. In order to provide some experimental simulation of asperity deformation in a manner amenable to observation, a special apparatus to model asperity deformation was devised where a hard wedge was drawn over a soft slab [106]. Deformation of surface material in the worn slab was viewed in cross-section while tangential and normal contact forces can simultaneously be measured. Deformation of a body causes linear and angular displacements relative to the initial position of the body. The complete linear displacement, δ, can be expressed in its projections on the coordinate axes, where u is the displacement in the direction of the x-axis, v is the displacement in the direction of the y-axis, and w is the displacement in the direction of the z-axis.