How to Calculate the Force of Flowing Gaseous Oxygen?

[Seaningtime]

Hi guys, I am trying to calculate the force that gaseous oxygen would exert if it were to flow from a tube and come to a restriction in that tube.

I'm not sure if I am correct in my thinking, but so far, I think that the flow can be calculated by the size and length of the restriction, and then the pressure based on that flow

Pousielle's-->
Flow= (delta pressure * pi * r^4) / 8 * l * n

And from that flow you should be able to calculate the force

Force= density * flow volume * delta velocityNow, I'm thinking that this would work, but I'm not certain.
Any help would be appreciated!

 

[Seaningtime]

I'm also just confused as to which units I should be using for pressure, n, and what units flow will end up as?
Thanks