# Viscous fluid moving in a pipe

#### mary d

A viscous fluid is moving through a pipe. The flow is 2 x 10^-3 m3/s
then you have a second tube with a fluid with twice the viscosity which is moving in a pipe whose length is 3 times the original with a radius 1.5 times the original. The pressure difference across this new pipe is 1/3 that of the original. What is the flow in the new pipe?
Again I have no idea where to start. What is the formula? I wonder if anyone could figure out how fast my professor could travel down that pipe of course using the same diameter? Sorry I just had to say it. Thanks for any help!

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#### arcnets

mary d,
maybe I'm mistaken but it seems to me that this lecture goes thru hydrodnamics at a very quick pace, deriving some formulae for practical use by engineers or scientists. It looks to me like the lecture's intention is not a profound understanding of physical principles, but rather to give the students a 'toolbox' for further use. Please correct me if I'm wrong.

This problem looks like an exercise in Hagen-Poiseuille's law, which states

dp/dz = -8 eta R-2 v

where
z is horizontal position along pipe,
p is pressure at position z,
eta is viscosity of liquid,
R is radius of round pipe,
v is mean velocity of liquid.

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