Kapillärsträckan

Kapillärsträckan, also known as capillary rise, is a phenomenon observed in physics and chemistry where a liquid spontaneously rises within a narrow tube, or capillary. This upward movement is driven by the interplay of adhesive forces between the liquid and the tube walls, and cohesive forces within the liquid itself. When the adhesive forces are stronger than the cohesive forces, the liquid wets the surface of the tube. This wetting causes the liquid to be pulled upwards along the walls.

The height to which the liquid rises is inversely proportional to the radius of the capillary tube. A narrower tube will exhibit a greater capillary rise than a wider one. This is because the surface tension forces acting along the circumference of the liquid in the narrow tube are more significant relative to the weight of the liquid column that needs to be supported. The surface tension of the liquid also plays a crucial role; liquids with higher surface tension will rise higher in a capillary tube.

This principle is fundamental to many natural and industrial processes. In plants, capillary action allows water to be transported from the soil up through the xylem to the leaves, defying gravity. In everyday life, it can be observed when a paper towel absorbs spilled liquid or when ink spreads on paper. Industrially, understanding capillary rise is important in fields like chromatography, where it aids in the separation of substances, and in the study of porous materials. The phenomenon is described mathematically by the Jurin's law, which relates the capillary rise height to the surface tension, density of the liquid, gravitational acceleration, and the radius of the capillary.