The movement of fluid up or down a narrow tube is

The movement of fluid up or down a narrow tube is capillarity. Capillary action, also known as capillarity, is the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. This occurs because of the combination of two opposing forces: adhesion, the attraction between the liquid molecules and the inner surface of the tube, and cohesion, the attraction between the liquid molecules themselves. When the adhesion force is greater than the cohesion force, the liquid is pulled up the tube, and when the cohesion force is greater, the liquid is pushed down the tube. Capillarity is responsible for many natural phenomena, such as the ability of plants to transport water from their roots to their leaves, as well as some man-made ones, such as the operation of wicks in candles and the ink in fountain pens.