Poiseuille S Equation — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Poiseuille's Equation Applies to laminar, incompressible flow of Newtonian fluids through long cylindrical pipes. Model fluid as cylindrical shells moving at different velocities. Apply force balance between pressure difference and viscous drag force on a cylindrical element. Integrate the shear stress equation to find the parabolic velocity profile v(r). Integrate the velocity profile over the cross-sectional area to obtain total volumetric flow rate Q. Laminar flow (Reynolds number < ~2000) Newtonian fluid (constant viscosity) Incompressible fluid No-slip boundary condition at pipe walls Pipe length much greater than radius (L >> r) Confusing flow rate (Q) with flow velocity (v). Underestimating the effect of radius changes (doubling radius increases flow 16x, not 2x). Applying the equation to turbulent flow. Ignoring the viscosity dependence on temperature.