Figure 5.

Summary of shear force F_s versus surface separation D based on traces as in Fig. 4 (different symbols refer to different contact points). (Inset) The variation of the shear stress σ, defined as σ = F_s/A, where A is the Hertzian contact area, as a function of the shear rate $\dot{\gamma }$, where $\dot{\gamma }$ = v_s/D, v_s is the shear velocity and D is the separation between the two opposing surfaces; symbols correspond to contact points in the main figure.