Surface tension is the tendency of the surface of a liquid to behave like a stretched elastic membrane. There is a natural tendency for liquids to minimize their surface area. The obvious case is that of a liquid droplet on a horizontal surface that is not wetted by the liquid—mercury on glass or water on a surface that also has a thin film of oil on it. All liquid molecules exhibit cohesive forces binding them with each other. This cohesive bond exhibits a tensile strength for the surface layer and this is known as surface tension.
Surface tension may also be defined as the work (in Nm/m2 or N/m) required to create unit surface area of the liquid. The work is actually required for pulling up the molecules with lower energy from below, to form the surface. Another definition for surface tension is the force required to keep unit length of the surface film in equilibrium (N/m). The formation of bubbles, droplets, and free jets are due to the surface tension of the liquid.
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