  We calculate the normal capillary retention force that anchors a drop to a
solid surface in the direction perpendicular to the surface, and study the
relationship between such force and the Young-Dupre work of adhesion. We also
calculate the work necessary to create or destroy a patch of solid-liquid
interface by moving the triple line on a solid substrate. We argue that when
the capillary number is small and a drop is sliding on a surface at constant
speed, the lateral retention force is the major source of energy dissipation,
whereas viscous dissipation plays a minor role.
