what actually is surface tension??what is its direction?
Interfacial tension is a surface stress, not a vector ('Force'), and is proportional to the curvature of the interface. At a three-phase contact line, Young's equation is often used as a force balance equation- but that is only valid for a contact line, not the interface in general.
molecules repel when close and attract when distant using vander walls force of attraction. The molecules on the surface of a liquid are distant unlike those inside the bulk. As a result they attract each other causing surface tension.This force helps in preventing the surface molecules from getting drawn into the liquid bulk due to the net unbalanced forces.
A different way of explaining would be, this force prevents the addition of more surface area, hence minimizing the potential energy of the system, which could have been increased due to the free surface energy.
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