Inter-molecular force of attraction that exist between molecules of the same substance is known as cohesive force. This note provides us an information on types of inter-molecular force of attraction and molecular theory of surface tension. There are two types of intermolecular forces. They are Cohesive Force Adhesive Force
Surface tension is applied for thread on a soap, floating needle, formation of lead shots, dipping of brush in water, adding oil in stagnant water and so on. The potential energy per unit area of the surface film is surface energy. Surface tension T is numerically equal to surface energy. Surface is also called free energy because the mechanical work done can be released when the surface contracts.
If the liquid meniscus is horizontal there is no net force normal to the surface on the molecules lying on the upper surface . If the liquid meniscus is horizontal there is no net force normal to the surface on the molecules lying on the upper surface . The shape of a liquid meniscus depends on the result of cohesive and adhesive forces that exist on the molecules of the liquid which are in contact with the solid surface there may be three different cases of the resultant force