Taking an analogy from the major–loss for a laminar–flow
wl =
At this point, an engineering parameter called friction–factor, f is defined as
so that
for a laminar–pipe flow, and
in general. This equation is known as Fanning equation. Here, f is experimentally shown to be dependent on the surface roughness and Reynolds number, and is obtained from a plot called Moody’s plot:
so that 
for a laminar–pipe flow, and 
in general. This equation is known as Fanning equation. Here, f is experimentally shown to be dependent on the surface roughness 
and Reynolds number, and is obtained from a plot called Moody’s plot:
