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Capillary action

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Definition

noun

The movement of a liquid, e.g. water molecules, through a narrow space as a result of cohesion, adhesion, and surface tension


Supplement

The capillary action pertains to the movement of a liquid through a narrow space as a result of the forces of cohesion, adhesion, and surface tension. Cohesion is the sticking together of alike molecules whereas adhesion is the sticking together of unlike molecules. Surface tension is the intermolecular attraction that pulls the molecules of the liquid inward from the surface resulting in the least surface area possible. These forces work together and produce a capillary action. If a capillary tube is made of glass or any other substance that is polar, water will spontaneously climb up inside it without having to be pumped in any way. The smaller the tube, the higher the water climbs. The attraction is so great between the water molecules and the molecules of the tube that water will climb in defiance of the force of gravity. Capillary action is seen in plants when water is able to ascent from the root upward through the xylem tissues of a plant. Water uptake involving capillary action is also seen in some small animals, e.g. Ligia exotica (sea roach) and Moloch horridus (thorny dragon).


Synonym(s):

  • capillarity
  • capillary motion
  • capillary effect
  • wicking

See also: