Virknisþrýstingi

Virknisþrýstingi, often translated as surface tension, is a phenomenon that occurs at the interface between a liquid and a gas, or between two immiscible liquids. It is the tendency of liquid surfaces to shrink into the minimum surface area possible. This effect arises from the cohesive forces between liquid molecules. Within the bulk of the liquid, molecules are attracted to each other equally in all directions. However, at the surface, molecules are attracted only by the molecules below and to the sides, leading to a net inward pull. This inward pull causes the surface molecules to be more tightly packed and exert a force that resists external forces, behaving as if the surface were a stretched elastic membrane.

Surface tension is responsible for various observable phenomena. For instance, it allows small insects, like water striders, to walk on the surface of water without sinking. It also causes water to form spherical droplets, as a sphere has the smallest surface area for a given volume. 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 also a direct consequence of surface tension working in conjunction with adhesive forces between the liquid and the walls of the narrow space. The unit of surface tension is typically force per unit length, such as newtons per meter (N/m), or energy per unit area, such as joules per square meter (J/m²).