# Q & A: force between hose nozzles

Q:
Dear Van,I have been wondering about something lately. Say you have two high-pressure hoses and you put them inside a swimming pool, with one nozzle being very close to the other one. If you open both nozzles at the same time, my understanding is that the nozzles would "repel" (move away from) each other.Now, if we have a hose and a vacuum tube inside a swimming pool, so that the later sucks water at the same rate the nozzle pushes water, then these two would "attract" (move towards) each other. I think.The question is, if I put two vacuum tubes very close to each other inside a swimming pool, and I turn them on at the same time, would the "repel" each other?This makes me think of Feynman's sprinkler problem, and also of like charges repelling each other but opposite ones attracting each other.
- Eddie Salazar (age 24)
Houston, Texas
A:

This is a great question. My answer will be less reliable than what nature tells you when you do the experiment.

Here's my guess. The force between the two nozzles will be approximately equal to the sum of the forces that each would produce if it were the only one with flow. A nozzle that is sucking in water will pull the oher toward it. I think that two nozzles each sucking water in will be more strongly attracted, not repelling. If instead one is an outlet and the other is an inlet, I think the total force will be small.

In addition, ther are Bernoulli forces, just to make life a bit more complicated.

But I'd love to hear the real results.

Mike W.

(published on 05/09/2019)