Capillary action, also known as capillary motion, capillary effect, capillarity, and wicking, can be defined as the property of a liquid that enables it to flow into narrow or porous spaces without the help of (and often in opposition to ) gravitational forces and other external forces. Capillary action is caused by a combination of two different types of intermolecular forces – cohesive forces and adhesive forces. The cohesive forces of the liquid and the adhesive forces that arise between the tube and the liquid, together, result in the rise of the liquid through the capillary tube. It can be noted that capillary action was first discovered and recorded by the Italian polymath Leonardo da Vinci.
Common examples of capillary action include the wicking of paint between the bristles of paintbrushes and the upward flow of water in plants (which is in a direction that opposes the force of gravity).