Computer-Vision Velocity Tracking Provides More Precise and Accurate Measurements of Kinetic Friction than the Traditional Angle-of-Slip Method

Abstract

Measuring the kinetic friction coefficient μₖ via the traditional incline-plane method relies on visually judging when a block slides at constant velocity. This judgment is subjective and introduces significant, hard-to-quantify uncertainty. In this study, we replace visual judgment with computer-vision velocity tracking: a wooden block was slid down six different surfaces inclined between 25°–65°, recorded at 60 fps, and analyzed with Tracker to extract acceleration from a linear v–t fit. We derive μₖ = tan θ − a/(g cos θ) from the v–t fit and use v²–x plots as a consistency diagnostic. The Tracker-based method yielded μₖ values that agreed closely with published engineering reference ranges [6] for wood and sandpaper (μₖ = 0.807 ± 0.039, literature range 0.60–1.00), and moderately for glass, while rubber and cloth showed larger deviations attributable to the specific materials tested. Across all six surfaces, the traditional visual method produced higher μₖ values than the Tracker method, by factors of roughly 1.5–6× over the angles examined here, consistent with tan θ at a visually-judged constant-velocity angle approximating the static friction coefficient μₛ rather than μₖ. We conclude that video-tracking analysis offers a more objective and reproducible alternative to the traditional angle-of-slip method, and one that aligns more closely with independent reference values, for measuring kinetic friction coefficients in the undergraduate physics laboratory.