Surface tension is the magnitude of the pulling force per unit length that causes tension and acts parallel to the surface of a liquid.
Mathematically, surface tension
\(=\frac{\text { Force }}{\text { Length }}( N / m )\) or \(\frac{\text { Surface energy }}{\text { Area }}\left( J / m ^{2}\right)\)
Surface tension is due to cohesion between particles of a liquid at the free surface. The surface tension of a liquid, in general, decreases with increase in temperature. The effect of pressure on surface tension is usually negligible. The surface tension of a substance can be changed considerably by impurities such as certain chemicals called surfactants (e.g. Soaps, detergents, camphor, alcohol, et cetera.) lowers the surface tension of water and enables it to penetrate the small openings between fibres for more effective washing.