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Which one governs, and under what conditions?","posed_since":"","precise":"Determine whether the dynamic angle $\\theta_d$ as a function of capillary number $Ca = \\eta U / \\gamma$ follows the hydrodynamic Cox-Voinov relation $\\theta_d^3 - \\theta_e^3 = 9 Ca \\ln(L/L_{\\mathrm{micro}})$, the molecular-kinetic relation $U = 2 \\kappa_0 \\lambda \\sinh(\\gamma (\\cos \\theta_e - \\cos \\theta_d) \\lambda^2 / (2 k_B T))$ with hopping frequency $\\kappa_0$ and site spacing $\\lambda$, or a combination, for advancing and receding lines. An answer is a law whose parameters are measured independently rather than fitted, valid for Ca from $10^{-6}$ to $10^{-1}$ across viscosity and wettability.","problem_ref":"0c51800ba644c3c86fb91379308c08c9654e29a164698e35d0024b8cf4cb6c7d","references":"","settled_by":"A data set over five decades of $\\mathrm{Ca}\\ (10^{-6}\\text{ to }10^{-1})$ for liquids of widely varying viscosity on well-characterized surfaces, with $L_{\\mathrm{micro}}$, $\\kappa_{0}$ and $\\lambda$ determined from independent measurements.","status_note":"","title":"Is there a predictive law for dynamic contact angle versus 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