Surface tension is the tension acting on both sides of any imaginary straight line on the liquid surface, perpendicular to the straight line and parallel to the liquid surface, and can make the liquid surface have a shrinking trend.

The magnitude of surface tension is related to the nature of the liquid and the properties of adjacent substances outside the liquid surface, as well as the temperature and impurities contained in the liquid surface. From a microscopic point of view, The surface tension is due to the interaction between molecules in the liquid surface layer, which is different from that in the liquid (water molecules are composed of two hydrogen atoms and one oxygen atom. Each water molecule has six bonds, making it connected with the other six adjacent water molecules. The positions of these six bonds are up, down, left, right, front and back respectively. But the water molecules on the surface of water have no neighbors, so they have redundant bonds. It is these redundant bonds that make the water molecules on the surface of water more closely connected than the water molecules inside water. This forms water Surface tension), so that the surface layer has a special property.