Kapillaarjõu

Kapillaarjõu, often translated as capillary force, refers to the phenomenon where liquid can flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. This effect is observed in narrow tubes, porous materials, and biological systems. It arises from the interplay of cohesive forces between liquid molecules and adhesive forces between the liquid and the surrounding surfaces.

When a liquid comes into contact with a solid surface, adhesion causes the liquid molecules to be attracted to the surface. If these adhesive forces are stronger than the cohesive forces between the liquid molecules themselves, the liquid will tend to spread out and wet the surface. In narrow spaces, this tendency, combined with the surface tension of the liquid, creates a force that can pull the liquid upwards or draw it into the material.

The magnitude of the capillary force is dependent on several factors, including the surface tension of the liquid, the contact angle between the liquid and the solid, and the radius of the narrow space. A smaller radius leads to a stronger capillary effect. For instance, water's ability to rise in the narrow xylem vessels of plants is a direct result of capillary action, essential for transporting water from the roots to the leaves against gravity. Similarly, capillary forces play a role in how liquids are absorbed by paper or cloth.