if by Poiseuille’s Law, the greater the radius/diameter of a tube the faster the flow, why does water flow faster out of a hose when you put your thumb over the nozzle?
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It sound like Poiseuille’s Law has more to do with the viscosity of the fluid. Like if you suck water through a straw then compare that with a straw that’s two times the diameter, it’s almost the same but if you suck a milk shake through the same straws, there will be a bigger difference.
Edit, from wik “Poiseuille’s equation describes the pressure drop due to the **viscosity** of the fluid”
“The assumptions of the equation are that the fluid is incompressible and Newtonian; the flow is laminar through a pipe of **constant circular cross-section** that is substantially longer than its diameter; and there is **no acceleration of fluid** in the pipe.”
By putting your thumb over the end, you’re changing the cross section and accelerating flow. Also you’re comparing the two with the same viscosity water.
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