What Is Capillary Action Definition and Examples

Capillary action definition: Capillary action describes the spontaneous flow of a liquid into a narrow tube or porous material. This movement does not require the force of gravity to occur. In fact, it often acts in opposition to gravity. Capillary action is sometimes called capillary motion, capillarity, or wicking. Examples of capillary action include the uptake of water in paper and plaster (two porous materials), the wicking of paint between the hairs of a paintbrush, and the movement of water through sand. Capillary action is caused by the combination cohesive forces of the liquid and the adhesive forces between the liquid and tube material. Cohesion and adhesion are two types of intermolecular forces. These forces pull the liquid into the tube. In order for wicking to occur, a tube needs to be sufficiently small in diameter. History Capillary action was first recorded by Leonardo da Vinci. Robert Boyle performed experiments on capillary action in 1660, noting a partial vacuum had no effect on the height a liquid could obtain via wicking. A mathematical model of the phenomenon was presented by Thomas Young and Pierre-Simon Laplace in 1805. Albert Einsteins first scientific paper in 1900 was about capillarity. See Capillary Action Yourself An excellent easy demonstration of capillary action is done by placing a celery stalk in water. Color the water with food coloring and observe the progress of the dye up the celery stalk. The same process may be used to color white carnations. Trim the bottom of a carnation stem to make sure it can absorb water. Place the flower in dyed water. The color will migrate via capillary action all the way to the flower petals. A less dramatic but more familiar example of capillary action is the wicking behavior of a paper towel used to wipe up a spill.