Drop retention force as a function of rested time

The force, f, required to slide a drop past a surface is shown to be a growing function of the time, t, the drop waited resting on the surface prior to the commencement of sliding along it. In this first report on the ``rest time'' effect we demonstrate the existence of this phenomenon in different systems, which suggests that this phenomenon is general. We show that df/dt is never negative. The shorter the resting times, the higher df/dt is. As the resting time increases df/dt decreases towards zero (plateau) as t tends to infinity. We attribute this phenomenon to the corrugation of the surface by the drop due to the unsatisfied normal component of the Young equation.