Fig. 3. Shear and normal forces in isolated gecko setal arrays on a glass surface. Motion in normal and shear axes was controlled at 50 µm s^-1. (A) Setal array during load (1), drag (2) and pull (3) (LDP) against the curvature of the setal shafts exhibits Coulomb friction. Negative F_|| represents the reaction forces during a drag to the left. However, no difference between static and kinetic friction was evident. Compression force F was approx. 3.2 times shear force F_||. (B) Setal array during LDP with the curvature of the setal shafts compressed initially, and then was pulled into tension as the setal tips adhered. Positive F_|| represents the reaction forces during a drag to the right. Adhesion was sustained during the 100 µm drag step (2). (C) Normal vs shear force during LDP against curvature of the setal shafts. F and F_|| followed a path along the Coulomb friction cone (red broken line of slope 1/µ). (D) Normal vs shear force during LDP with curvature of the setal shafts. F and F_|| followed a path that began initially along the Coulomb friction cone (red broken line of slope 1/µ). As adhesion developed, the forces converged on F=-F_||tan^*, where ^*30° (blue broken line).