Calculates pressure drop (head loss) of a fluid, in straight circular pipes due to friction. Input parameters for this app is pipe diameter, lenght of pipe, pipe roughness (app includes default values for widely used pipes), flow rate in several expressions, and physical properties of the flow medium). At first the Darcy friction factor f,is calculated depending upon the type of flow that exist in the pipe. So, if Reynolds number is less than 2000 (laminar flow), the f=64/Re formula is used to calculate the friction factor f. If Reynolds number is more than 2000 (transition or turbulent flow), an approximation of the Colebrook equation (Swamee-Jain equation) is used in order to calculate friction factor f. Then Darcy-Weisbach equation is used finally to calculate the pressure loss.