Pinnankireydessä

Pinnankireydessä, known in English as surface tension, is a property of liquids that causes the surface of the liquid to behave like an elastic membrane. This phenomenon arises from the cohesive forces between liquid molecules. Within the bulk of the liquid, molecules are attracted equally in all directions by neighboring molecules. However, at the surface, molecules are attracted only by molecules below and beside them, resulting in a net inward force. This inward force pulls the surface molecules closer together, minimizing the surface area and creating a tension.

Surface tension is responsible for several observable phenomena. It allows small insects, like water striders, to walk on water without sinking. It also causes water to form droplets when spilled or in a fine spray. Capillary action, the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity, is another consequence of surface tension, along with adhesive forces between the liquid and the surface it is in contact with. The strength of surface tension varies depending on the liquid; for example, water has a relatively high surface tension due to its strong hydrogen bonding.