Mechanical Definition Surface Energy and Capillary Force

L2 Mechanical Definition Surface Energy and Capillary Force 

It is well known that supplying energy is necessary to create surfaces. That fact is plainly obvious when you beat egg whites into a meringue or when you make an emulsion of water in oil while preparing a mayonnaise. 

Suppose one wants to distort a liquid to increase its surface area by an amount dA. The work required is proportional to the number of molecules that must be brought up to the surface, i.e., to dA and one can write  

7 is the energy that must be supplied to increase the surface area by one unit 

Surface tension also contributes to thermodynamic work. It can be defined as the increase in internal energy U or in free energy F that accompanies an increase in surface area  

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