Capillarity describes the movement of liquid in small spaces without external forces acting on it. The capillarity is driven by surface tension and adhesive interactions between the liquid and surrounding solid surfaces. This effect is often seen in narrow tubes, porous materials, and fine particles.

Surface tension is crucial to capillarity. It results from cohesive forces between liquid molecules at the liquid-air boundary, forming a skin that resists external forces. When the capillary tube is placed in a liquid, the liquid level changes based on the adhesive interactions between the liquid and the tube's surface. If these adhesive forces are greater than the liquid's cohesive forces, the liquid rises in the tube, known as capillary rise. If the cohesive forces are stronger, the liquid level drops, known as capillary depression.

The height to which the liquid rises or falls in a capillary tube is influenced by several factors, including the liquid's surface tension and density, the contact angle between the liquid and the tube, gravitational acceleration, and radius of the tube.

Capillarity is involved in many natural and industrial processes. It affects soil water and nutrient movement, which is essential for plant growth. In porous materials, it impacts liquid absorption and retention. Capillarity is also used in technologies like inkjet printing and microfluidics.