Capillary action is the phenomenon where a liquid rises inside a small-diameter tube, such as a capillary, due to adhesive forces between the liquid and the inner walls of the tube. This effect is particularly noticeable in narrow tubes and is governed by a balance between cohesive and adhesive forces.

Capillary action is the term used to describe the rise of a liquid inside a small-diameter tube due to adhesive forces between the liquid and the tube's inner walls.

Adhesive forces are the attractive forces between molecules of different substances. In the case of capillary action, the adhesive forces between the liquid and the tube's inner walls are stronger than the cohesive forces between the liquid molecules. This results in the liquid being drawn upward inside the tube.

Capillary action can be explained using the following key points:

1. Adhesive forces: Adhesive forces are the forces of attraction between the liquid molecules and the molecules of the tube's inner walls. These forces arise due to the interaction between the molecules at the interface. In the case of capillary action, the adhesive forces are stronger than the cohesive forces within the liquid.

2. Cohesive forces: Cohesive forces are the forces of attraction between molecules of the same substance. These forces hold the liquid molecules together. In the case of capillary action, the cohesive forces within the liquid are not strong enough to overcome the adhesive forces between the liquid and the tube's walls.

3. Small diameter of the tube: Capillary action is more pronounced in tubes with small diameters. This is because the surface area of the liquid in contact with the tube's walls is larger in small-diameter tubes, resulting in stronger adhesive forces.

4. Rise of the liquid: Due to the stronger adhesive forces, the liquid is pulled upward inside the tube against the force of gravity. The height to which the liquid rises is determined by the balance between the adhesive and cohesive forces, as well as the diameter of the tube.

Capillary action has several important applications, such as in the movement of water through plant roots, the functioning of capillary tubes in medical devices, and the rise of ink in a fountain pen. Understanding capillary action is crucial in fields like fluid mechanics, biology, and materials science.