hi everyone this is my first thread on this board and sorry for any missing in English because it's not my native language i just want to calculate the pressure drop base on pipe-flo pro document which has been share in this thread https://www.physicsforums.com/showthread.php?t=179830. my question is about equation1 in this paper. dP = fρ(L/D)v2/2g Is it correct for gravitational term to be in these d-w equation's form??? And if it's correct, where is "g" come from???