A capillary tube is a thin, narrow tube that allows liquids to move through it due to capillary action. This phenomenon occurs when the adhesive forces between the liquid and the tube's walls are stronger than the cohesive forces within the liquid. Capillary tubes are commonly used in various applications, including laboratory experiments and medical devices. These tubes are often made of glass or plastic and can have diameters as small as a few micrometers. In nature, capillary tubes can be found in plants, where they help transport water and nutrients from the roots to the leaves, demonstrating the importance of capillary action in biological systems.