Measured friction coefficients obtained from the bridge force signals. The plots at the top show the measured friction coefficients, while the ones at the bottom represent the second-order polynomial fits to the measured friction coefficients using equation (5). (a) Static friction coefficient μ_s. (b) Dynamic friction coefficient at the first slip μ_d1. (c) Averaged “dynamic” friction coefficient μ_d, computed by taking the ratio of the average bridge force on the bowing plane and the average bridge force on the perpendicular plane over a 0.1 s time window.