The dynamics of the deformations of a moving contact line is studied assumi
ng two different dissipation mechanisms. It is shown that the characteristi
c relaxation time for a deformation of wavelength 2 pi/\k\ of a contact lin
e moving with velocity nu is given as tau (-1)(k) = c(nu)\k\. The velocity
dependence of c(nu) is shown to depend drastically on the dissipation mecha
nism: we find c(nu)=c(nu =0)-2 nu for the case in which the dynamics is gov
erned by microscopic jumps of single molecules at the tip (Blake mechanism)
, and c(nu) similar or equal toc(nu =0)-4 nu when viscous hydrodynamic loss
es inside the moving liquid wedge dominate (de Gennes mechanism). We thus s
uggest that the debated dominant dissipation mechanism can be experimentall
y determined using relaxation measurements similar to the Ondarcuhu-Veyssie
experiment [T Ondarcuhu and M. Veyssie, Nature 352, 418 (1991)].