In short
Surface tension is the force acting along the surface of a liquid, per unit length, that makes the surface behave like a stretched elastic skin. It is measured in newtons per metre.
Molecules inside a liquid are pulled equally in all directions. A molecule at the surface is pulled mainly inwards by its neighbours, so the surface tries to become as small as possible. This is why drops and bubbles are round and why small insects can walk on water. Surface tension is also the surface energy per unit area, and it falls as the temperature rises.
Water has a surface tension of about at . A film pulling on a long wire exerts a force of , because it has two surfaces.
Also searched as: surface tension and surface energy.
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