Capillary action, capillarity, capillary motion, or wicking refers to two phenomena:
A common apparatus used to demonstrate the first phenomenon is the capillary tube. When the lower end of a vertical glass tube is placed in a liquid such as water, a concave meniscus forms. Adhesion forces between the fluid and the solid inner wall pulls the liquid column up until there is a sufficient mass of liquid for gravitational forces to overcome these intermolecular forces. The contact length (around the edge) between the top of the liquid column and the tube is proportional to the diameter of the tube, while the weight of the liquid column is proportional to the square of the tube's diameter, so a narrow tube will draw a liquid column higher than a wide tube.
Read more about Capillary Action: Examples, Height of A Meniscus, Liquid Transport in Porous Media, Miscellaneous
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