How does surface tension arise?
Surface tension is related to the energy required to increase a liquid's surface area. Molecules inside the liquid interact with neighbors in all directions, whereas surface molecules have a different environment. This difference explains the tendency to minimize surface area under appropriate conditions.
Droplets and molecular interactions
Small airborne water droplets approach a spherical shape, which minimizes area for a fixed volume. Gravity distorts larger drops, so droplets are not always perfect spheres. Temperature and dissolved substances affect surface tension. Surfactants such as soap change surface properties and can promote wetting. Surface tension can be expressed as force per unit length or, equivalently, energy per unit area.
Observations and applications
Some insects stand on water because deformation of the interface supplies supporting forces, not because a solid membrane forms. Explaining liquid rise in glass or absorption by paper also requires adhesion, contact angle, and pore size. These properties matter in detergents, paints, and coatings. Dirty containers or trace contaminants can substantially alter an experiment.