The Mobility of Drops, Pearls, and Marbles

At the scale of drops, water either sticks to inclined solids or moves, yet slowly-without the mobility we expect of a liquid of low viscosity. We first recall that the contact line that bounds a drop is responsible for these special adhesion and enhanced friction properties. Then, we discuss how inducing nonwetting states (pearls and marbles) minimizes the role of this line, restores mobility, and even boosts the liquid when it is viscous.