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?

Question

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?

In: 7

Answer 1

Poiseuille is for the entire hose. You’re changing the end only.

https://www.physlink.com/education/askexperts/ae185.cfm#:~:text=When%20you%20put%20your%20finger%20over%20the%20tip%20of%20the,water%20flowing%20out%20a%20constant).

https://physics.stackexchange.com/questions/384972/why-water-can-fly-faster-then-slower-when-you-press-the-water-hose-with-your-t

As the other poster said, you might be confusing the stream velocity for the volumetric flow rate. Another thing that comes into play is that if the flow in the hose is reduced because of the nozzle, the frictional losses in the hose are less.