why does boundary layer thickness increases along the the length of plate in fluid mechanics?

Question

thickness of boundry layer increases gradually along the plate from leading edge to trailing edge.why does this thickness increases where there is a reduction in velocity and frictional resistance is same

Answer 1

The answer to the boundary layer growth is the same to the velocity reduction: Viscosity. In fact, the boundary layer thickness its defined in terms of this velocity reduction (the 99% criteria). As more the velocity reduction effect penetrates on the free stream, more thicker would be the boundary layer. The best explanation to these subject could be found at Schlichting book (Boundary Layer Theory, chapter 7). But any text of Fluid Mechanics should have a section where the solution to Blasius equation is developed.

Answer 2

I don't think the frictional resistance is constant along the flow length....
But here is a good document going into the detail of boundary layer thickness:
http://web.engr.oregonstate.edu/~shepheju/drag%20reduction.doc

Answer 3

I'm sure your book has the answer