Capillary action

Capillary action is a process in physics and fluid dynamics that allows liquids to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. This phenomenon is due to the intermolecular forces between the liquid and the surrounding solid surfaces.

Overview

Capillary action is observed in thin tubes, or capillaries, where the combination of surface tension and adhesive forces between the liquid and the tube material can cause the liquid to climb the sides of the tube. This effect can be seen in everyday phenomena such as the absorption of water by a paper towel, the movement of groundwater in soil, or the rising of sap in plant stems.

Mechanism

The mechanism of capillary action is based on the cohesive and adhesive forces in the liquid. Cohesion is the attractive force between like molecules, which holds the liquid together, while adhesion is the attractive force between different types of molecules, such as the liquid and the solid tube material.

When the adhesive forces are stronger than the cohesive forces, the liquid will spread out and climb the sides of the tube, forming a concave meniscus. Conversely, if the cohesive forces are stronger, the liquid will pull together and form a convex meniscus.

Applications

Capillary action has numerous applications in various fields. In biology, it is essential for the transport of water and nutrients in plants. In medicine, it is used in capillary tubes to collect blood samples. In engineering, it is utilized in the design of devices such as inkjet printers and heat pipes.

See also

• Surface tension
• Fluid dynamics
• Cohesion (chemistry)
• Adhesion (chemistry)