Surface tension is a property of liquids that describes the tendency of a liquid’s surface to behave like an “elastic film.” It arises from the cohesive forces between the molecules of the liquid—that is, the attractive forces holding the molecules together.

Inside the liquid, each molecule is surrounded by others and experiences balanced forces in all directions. However, at the surface, molecules are not completely surrounded; they are pulled more strongly inward and sideways. This results in a net force that causes the surface to minimize its area.

This phenomenon explains why droplets tend to form spherical shapes: a sphere has the smallest surface area for a given volume. Surface tension is measured in newtons per meter (N/m) and depends on the nature of the liquid and its temperature.

For example, water has a relatively high surface tension due to hydrogen bonding between its molecules. This is what allows certain insects, like water striders, to walk on water without sinking.

Surface tension plays a crucial role in many natural phenomena and technological applications: in bubble formation, capillary action, detergents, inkjet printing, and even water transport in plants.