1. The problem statement, all variables and given/known data I'm not sure if this is introductory or not but here goes anyway... So we have this experiment to measure the flow rate of viscous fluids by forcing them up a measuring tube using some compressed air in a drum. The idea is to test the limits of poiseuilles law with various different viscosity fluids. So we first decided to model the system. Using the Hagen-Poiseuille equation we end up with an expression for pressure (constant) and height as a function of time, but we have two height variables and I'm not sure how to deal with them. I'll show my working in a minute but basically my supervisor says we are along the right lines but there is more to be done. I'm not exactly sure how to continue with this problem. Any advice would be most welcome. p- Pressure r - radius h - height of tube Q - flow rate μ - Viscosity The equations come in the next section....I hope that all makes sense, if its a bit confusing its because this is the format we are required to present in. 2. Relevant equations Poiseuilles law - ∆p=8μhQ / r^4π Q (volumetric flow rate) = πr^2h 3. The attempt at a solution My supervisor said 'h' (there's two h variables here) is not constant. So if I make one 'h' a dh/dt ( so we have a discretized volumetric flow rate) then I can make the other h a function of time right? The rest is constant (pressure is also constant in our experiment as we will make it so!) so we end up with the following Subbing in to poiseuilles equation for Q gives us --> ∆p = 8μ h(t) dh/dt / r^2 Pressure is constant ( I'll call it P from now on. I'll also group and rename all the constant variables on the right hand side to k. So we end up with P = k * h(t) dh/dt I'm thinking that if I just isolate h(t) then I have my solution right? But moving k over to the left and the dh/dt would give us (P/k) / dh/dt = h(t) --> Pdt / kdh = h (t) Can I even do this? This is the point at which I become confused... Although I also think if this is correct then its just the exponential function right? I know most of these equations end up as being the exponential function and it would make sense for h(t) to be an exponential decay because; the resistance to flow increases in the tube proportionally to pressure. I'm just not sure I'm explaining/deriving it correctly or how to... Thanks.