Question on Fluid Pressure in Pipes

[!Live_4Ever!]

Hi, I was doing my fluid mechanics howework, and there was a question that I couln't quite answer.

Assuming that the integral of the axial momentum remains constant along the pipe cross section, the pressure drops uniformly along the pipe length. (Contrary to the Bernulli equation where the pressure is supposed to stay constant)

I was wondering if anyone had a non-mathematical way of explaing why a pressure drop exists in a pipe with uniform diameter..

Thanks, as always.

 

[rock.freak667]

In all pipes there is a relative roughness which is associated with a friction factor. This friction can cause pressure drops.