Editing Capillary action (section)

{{Short description|Ability of a liquid to flow in narrow spaces}}
[[File:Capillary flow brick.jpg|thumb|Capillary water flow up a 225 mm-high porous brick after it was placed in a shallow tray of water. The time elapsed after first contact with water is indicated. From the weight increase, the estimated porosity is 25%.]]
{{Continuum mechanics}}

[[File:Capillarity.svg|thumb|Capillary action of [[water]] (polar) compared to [[Mercury (element)|mercury]] (non-polar), in each case with respect to a polar surface such as glass (≡Si–OH)]]

'''Capillary action''' (sometimes called '''capillarity''', '''capillary motion''', '''capillary rise''', '''capillary effect''', or '''wicking''') is the process of a [[liquid]] flowing in a narrow space without the assistance of external forces like [[Gravitation|gravity]].

The effect can be seen in the drawing up of liquids between the hairs of a paint-brush, in a thin tube such as a [[Drinking straw|straw]], in porous materials such as paper and plaster, in some non-porous materials such as [[clay]] and liquefied [[carbon fiber]], or in a [[biological cell]].

It occurs because of [[intermolecular force]]s between the liquid and surrounding solid surfaces. If the diameter of the tube is sufficiently small, then the combination of [[surface tension]] (which is caused by [[Cohesion (chemistry)|cohesion]] within the liquid) and [[Adhesion|adhesive forces]] between the liquid and container wall act to propel the liquid.