Surface tension is a property of the surface of aliquid. It is what causes the surface portion of liquid to be attracted to another surface, such as that of another portion of liquid (as in connecting bits of water or as in a drop of mercury that forms a cohesive ball).
Surface tension is caused by cohesion (the attraction of molecules to like molecules). Since the molecules on the surface of the liquid are not surrounded by like molecules on all sides, they aremore attracted to their neighbors on the surface.
Applying Newtonian physics to the forces that arise due to surface tension accurately predicts many liquid behaviors that are so commonplace that most people take them for granted. Applyingthermodynamics to those same forces further predicts other more subtle liquid behaviors.
Surface tension has the dimension of force per unit length, or of energy per unit area. The two are equivalent—but when referring to energy per unit of area, people use the term surface energy—which is a more general term in the sense that it applies also to solids and not just liquids.
In materials science, surface tension is used for either surface stress or surface free energy.
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