Capillary phenomenon is closely related to wetting phenomenon. When a capillary tube is inserted into a liquid, a height difference will be generated inside and outside the tube. If the liquid can wet the tube wall, the liquid level inside the tube will be higher than outside the tube, and the liquid level is concave. Otherwise, the liquid level inside the tube will be lower than outside the tube, and the liquid level is convex.
Take the wetting situation as an example (such as water and glass tube): Since the adhesion is greater than the cohesion, the contact angle 0 < 90°, so the liquid surface is concave. The contact angle refers to the angle between the cut surface of the liquid surface and the solid surface at the edge of the surface where the liquid and the solid touch.
The concave surface makes the resultant force of the surface tension an upward force, so that the liquid level in the tube rises to the point where the weight of the liquid column of the raised part is equal to the resultant force of the surface tension.
Capillary phenomenon is often seen in daily life, such as when one end of a towel is immersed in water, its upper part will gradually get wet, the water absorption effect of blotting paper, and the evaporation of water inside the soil.
