Surface Tension
Surface tension is the energy per unit area due to having a surface in a liquid. It has the dimension of force per unit length, or energy per unit area. The two are equivalent, but when referring to energy per unit of area, it is common to use the term surface energy, which is a more general term in the sense that it applies also to solids. Surface tension is used for liquids, while surface stress and surface energy are more commonly used for solids.
An example of its relevance is the tendency of liquid surfaces at rest to shrink to the minimum surface area possible. Because of the relatively high attraction of water molecules to each other through a web of hydrogen bonds, water has a higher surface tension (72.8 millinewtons (mN) per meter at 20 °C) than most other liquids. This allows objects with a higher density than water such as razor blades and insects (e.g. water striders) to float on a water surface without becoming even partly submerged.
The magnitude of the surface tension is connected to the forces between the molecules at the surface. Therefore surfactants are often used to reduce it so there is more contact between the liquid and another material, for instance detergents. It can also lead to pressure inside water bubbles, as well as many other phenomena; it is a classic, well-studied property common to all liquids.
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