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surface tension

a needle supported by surface tension
Surface tension effects allow adapted insects to "skate" on the surface of a pond, or a needle to be "floated" in a cup of water.
The force existing in any boundary surface of a liquid such that the surface tends to assume a minimum possible area. It is defined as the force perpendicular to a line of unit length drawn on the surface. Surface tension arises from the cohesive forces between liquid molecules and from the fact that a molecule in the interior of a liquid is pulled equally from all sides by its neighbors, whereas a molecule at the surface is only attracted by molecules below it in the liquid; it makes a liquid surface behave as if it had an elastic membrane stretched over it.

Surface tension is responsible for the formation of liquid drops and bubbles, and governs the wetting properties of liquids, capillary action, and the action of detergents. Water has an extremely high surface tension.

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