So Volume Flow Rate (Q) = (P2-P1)/R where R is the total resistance of the system. R is directly proportional to Length and inversely proportional to surface area, and the inherent resistance (viscosity) of the fluid. But R =nL/r^4. r^4 rather than r^2. So there has to be another factor other than just surface area, that is dependent on radius^2, affecting resistance right? What am I missing? ________________________ In terms of Volume Flow Rate Q, i can understand, since Q = Av and if you change r, you change not only the surface area but also the velocity since the pipe is larger so there is less resistance. A = pi*r^2 AND v is related to radius by a squared factor.