Poiseuille's Law describes the

fluid flow through a

cynlindrical pipe of length

**L** and

cross-sectional radius

**R**, the equation is given by:

**J** = πR^{4}(P_{i} - P_{o}) / 8ηL

where P_{i} - P_{o} is the pressure differnce between the two ends of the pipe. (input minus output)

η is just the viscosity of a fluid.