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capillary action

The cohesion between a liquid and a solid results in the liquid surface curving near the solid, to meet it at a definite angle. Water curves upward against glass, and the force of cohesion is exerted along the water surface, tending to lift it. The lifting force is proportional to the circumference of the water surface; in a narrow tube this force becomes powerful enough to lift a tall column of water.
Also called capillarity, the name given to various surface tension phenomena in which the surface of a liquid confined in a narrow-bore tube rises above or is depressed below the level it would have if it were unconfined. When the attraction between the molecules of the liquid and those of the tube exceeds the combined effects of gravity and the attractive forces within the liquid, the liquid rises in the tube until equilibrium is restored.

Capillary action is very important in nature, particularly in the transport of fluids in plants (see xylem) and through the soil.

Related entry

   • capillary constant

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