How does capillary action work?
Capillary action is liquid movement in narrow channels or porous materials caused by interfacial forces. Water may rise in a glass tube, while other liquid-surface combinations show a depressed level. The material in contact with the liquid matters as much as the liquid itself.
Adhesion, cohesion, and contact angle
Attraction between liquid molecules is cohesion, while attraction to another surface is adhesion. Together with surface tension, these interactions determine meniscus shape and contact angle. In a narrow wetting tube, equilibrium rise generally increases as radius decreases. Surface forces balance the weight of the raised liquid. A single-tube model is only approximate for irregular pore networks.
Plants and porous materials
Towels absorbing water, ink spreading through paper, and soil retaining moisture involve capillary effects. Water transport to the tops of tall trees, however, also relies on transpiration and the cohesion-tension mechanism. Rising damp in buildings depends on pore structure. The speed of advance is distinct from equilibrium height; viscosity affects how quickly liquid moves.