Young's contact-angle equation (${\gamma }_{SV}-{\gamma }_{SL}={\gamma }_{LV}\cos \theta$)

The planar interfacial balance ${\gamma }_{SV}-{\gamma }_{SL}={\gamma }_{LV}\cos \theta$ for the equilibrium contact angle through the liquid, with interfacial free energies defined per actual area. Roughness and retained air require additional area accounting.