In the resistance equation R=8L(eta)/pi(r^4), where does the r^4 come from?

Question

Where eta is the viscosity of the fluid, L is the length of the tube, and r is the radius of the tube.

Also, if you can just derive it, that would be awesome.

Thanks!

Answer 1

This is interesting, since it has an electrical analogy as well. Check out the wiki article on "Poiseuille's law", it gives a good explanation how the equation is derived.