Poiseuille's Law

An analytical expression for laminar, incompressible, Newtonian flow through a straight, rigid cylindrical conduit stating volumetric flow rate Q = (π r^4 ΔP)/(8 μ L), where r is radius, ΔP the pressure drop, μ the fluid viscosity and L the conduit length. It assumes fully developed laminar flow, no slip at walls, and rigid circular geometry.