1) Surface Tension- Free surface of a fluid behaves like a stretched membrane and tries to minimise its area upto maximum possible extent. This property is known as surface tension.
Note: 1)Free surface is a surface with constant normal stress and zero shear stress. 2) Normal stress is always equal to the pressure and zero shear stress means no external force in tangential direction.
Mathematically, Surface Tension= Force (F)/ Length (l)
2) Adhesive and Cohesive force- Adhesive force is the attraction force between the unlike molecules. Cohesive force is the attraction force between the molecules of same substance.
Note: 1) If adhesive force>> cohesive force, liquid will wet the solid boundary and the liquid is called wetting liquid. Eg: water glass interface 2) If cohesive force >> adhesive force, liquid is called non-wetting liquid. Eg: Glass mercury interface.
Mechsiast 