[Shamoon Jamshed]

Hi,

I found in some article that the pressure gradient for a smooth pipe is dp/dx = 0 for fully developed laminar/turbulent flow. If we accept the fact then, there would be no friction at all because the pressure has not been dropped along the length. Can someone explain the theory to me please? May be I am misunderstanding some point.
What about the favourable pressure gradient, and I am talking about both laminar and turbulent flows.