Example. Liquid coating on a solid substrate (Fig. 3.3).

Fig. 3.4 :Liquid film on a solid surface   

Navier-Stokes equation reduces to-

From the no-slip condition, at

We take another assumption – that the bounding fluid is less viscous than the film. This would mean that the bulk fluid does not offer any drag or shear force on the film.

from the no-slip condition.