1. The problem statement, all variables and given/known data The horizontal pipe is very large and long: 100 feet in diameter and 1500 feet long with an infinite supply of air on both ends. The pressure difference between the two ends is 0.6 psi. I assume friction is near zero as the pipe is so big so I ignore it. What is the velocity of the air that flows through it. The density of the air is 1.2 grams/liter at 20 degrees C.(I converted all units to same system) kinematic viscosity of the air is 1.64 x 10-4 ft2/sec dynamic viscosity of the air is 3.82 x 10-7 lbf sec/ft2 2. Relevant equations Which viscosity do I use for the formula. I thought the dynamic viscosity because the units work out but that gives an even more ridiculous answer. 3. The attempt at a solution I have tried to use Poiseuille's equation of v= (P1 - P2)(3.124)r4/8L and I get an outrageous answer of 800,000,000 cubic feet per second. What am I doing wrong?