What is water's surface tension?

Answer 1

Here are some explanations of surface tension:

• Surface tension is a property of the surface of a liquid that causes it to behave as an elastic sheet. It allows insects, such as the water strider (pond skater, UK), to walk on water too. It allows small objects, even metal ones such as needles, razor blades, or foil fragments, to float on the surface of water, and it is the cause of capillary action.
• 5.18 pounds / feet at 0 degree Celsius. Or as I remember it is 72 dyne / centimeter at 25 degree Celsius. The surface tension of water is the force required in order to float at the water's surface, hence making water to behave like an elastic sheet.
• Water surface tension is contractive tendency of the surface of a liquid that allows it to resist an external force. The beading of water on a waxy surface, such as a leaf, is an example of water surface tension.

Answer 2

Surface tension is produced at the boundary between a liquid (not just water) and air. It is caused because within the liquid the molecules are equally attracted in all directions by other molecules of the same liquid, but at the boundary they are only attracted in the direction of the liquid not in the direction of the air. The balanced attraction of liquid molecules exactly in the plane of the boundary creates the actual tension on the liquid surface.