Surface Tension Effects

Surface tension is a cause of the fact that small water drops in air and small gas bubbles in water take up a spherical form. Surface tension is a consequence of intermolecular cohesive forces. When one of two media in contact is a liquid phase, work must be done on a molecule approaching the interface from the interior of the liquid because this molecule experiences an unbalanced cohesive force directed away from the interface. This results in a higher potential energy for the molecules at the interface and a tendency for all molecules of the liquid near the interface to move inward. The interface therefore tends to contract as if it were in a state of tension like a stretched membrane. Since, in a state of equilibrium, the interface energy must be a minimum, for a given volume, the sphere is the shape with the least surface area. A water drop in air and an air bubble in water are therefore spherical.