Surface tension is a property of the surface of a liquid that allows it to resist an external force, due to the cohesive nature of the liquid. It is the tendency of fluid surfaces to shrink into the minimum surface area possible. Surface tension is not a property of the liquid alone, but a property of the liquids interface with another medium. The surface of any liquid is an interface between that liquid and some other medium, such as air or a container wall. Surface tension depends mainly upon the forces of attraction between the particles within the given liquid and also upon the gas, solid, or liquid in contact with it. The energy responsible for the phenomenon of surface tension may be thought of as approximately equivalent to the work or energy required to remove the surface layer of molecules in a unit area. Surface tension may be expressed in units of energy (joules) per unit area (square meters) .
Some key features of surface tension include:
- Cohesive forces: These are the forces that hold the body of a liquid together with minimum surface area/Physical_Properties_of_Matter/States_of_Matter/Properties_of_Liquids/Surface_Tension).
- Adhesive forces: These are the forces that try to make a body of a liquid adhere to a surface/Physical_Properties_of_Matter/States_of_Matter/Properties_of_Liquids/Surface_Tension).
- Surface molecules: These are compressed more tightly together at the surface, forming a sort of skin on the surface, with less distance between them compared to the molecules below them. Surface molecules also form a much smoother surface than one would expect from randomly moving molecules.
Surface tension can be observed in everyday life, such as when a paper clip floats on the surface of water.
