What is capillary action?

Capillary action refers to the ability of a liquid to move within narrow spaces without the assistance of external forces, primarily due to the combination of adhesive and cohesive forces. This phenomenon occurs when a liquid's surface tension causes it to rise or fall in a thin tube or narrow porous material.

In this process, the adhesive forces between the liquid molecules and the surfaces of the narrow spaces (for example, the walls of a small tube or the fibers in a porous material) are greater than the cohesive forces among the liquid molecules themselves. This interaction causes the liquid to be pulled upward or downward, allowing it to flow against gravity.

Capillary action is essential in various natural and artificial systems, such as water transport in plants, ink movement in pens, and the behavior of liquids in small openings. Understanding this concept is crucial in fields like engineering, where the flow of fluids in small spaces can significantly impact design and functionality.