Equations · equation
Poiseuille's Law
Fluid Dynamics · 1840
- Equation
- Q = π r⁴ Δp / (8 μ L)
- Field
- Fluid Dynamics
- Named After
- Jean Léonard Marie Poiseuille
- Symbols
- Q volume flow rate · r pipe radius · Δp pressure drop along the pipe · μ dynamic viscosity · L pipe length
- Year
- 1840
Significance
Laminar flow through a pipe goes as the fourth power of the radius: halve the bore and the same pressure moves one-sixteenth the fluid. Poiseuille was a physician measuring blood in glass capillaries in 1840; the law explains why a small narrowing of an artery matters so much, why a hydraulic line is sized as it is, and why a syringe with a fine needle takes so much force.
Open on the Equations shelf — the interactive card, the filters, and everything alongside it.