Capillary action<span> (sometimes </span>capillarity<span>, </span>capillary motion<span>, or </span>wicking<span>) is the ability of a </span>liquid<span> to flow in narrow spaces without the assistance of, or even in opposition to, external forces like </span>gravity<span>. The effect can be seen in the drawing up of liquids between the hairs of a paint-brush, in a thin tube, in porous materials such as paper and plaster, in some non-porous materials such as sand and liquefied </span>carbon fiber<span>, or in a cell. It occurs because of </span>intermolecular forces<span> between the liquid and surrounding solid surfaces. If the diameter of the tube is sufficiently small, then the combination of </span>surface tension<span> (which is caused by </span>cohesion<span> within the liquid) and </span>adhesive forces<span> between the liquid and container wall act to propel the liquid.</span><span>[1]</span>
