Hagen-Poiseuille equation

The Hagen-Poiseuille equation describes how the flow rate of a viscous fluid (like water or oil) moving through a cylindrical tube depends on various factors. Specifically, it shows that the flow increases with the fourth power of the tube's radius, meaning small changes in radius significantly affect flow. It also depends on the pressure difference driving the flow, the fluid’s viscosity (thickness), and the length of the tube. Essentially, it's a way to predict how much fluid will pass through a pipe based on these variables, helping engineers design systems like blood flow in arteries or plumbing networks.