vat is the reason behind the v^2(velocity squared) in Darcy-weisbach eqn?

Question

it is assumed that f' is the frictional resistance per unit wetted area per UNIT velocity.....then how come the term "v^2"

Answer 1

It is for velocity head. Often friction loss and typical loss coefficients are a function of velocity.

V = (2 g h)^0.5

V^2 = 2 g h

h = V^2/2g = velocity head