Young's law and the effects of interfacial energy on the pressure at the solid-fluid interface
In a recent paper [R. Finn, Phys. Fluids 18, 047102 (2006)] the attention has been drawn on the tension component perpendicular to the solid surface that results from Young's law. Considering the problem of a solid sphere floating in zero gravity, it has been argued that this component yields a spurious net vertical force acting on the sphere, which remains unbalanced. Therefore, the validity of Young's law has been questioned in favor of an energy argument. The scope of this Brief Communication is to restate the equivalence between the energy and the force descriptions of the problem. It is shown that there is no contradiction in Young's law if one accounts for the different stress acting on the solid surface in the two fluids. The net force resulting from the latter balances the force resultant associated with the tension component perpendicular to the solid. (C) 2007 American Institute of Physics.