Poiseuille's Law (16 tubes vs 1 tube)

The laminar flow rate of an incompressible fluid along a pipe is proportional to the fourth power of the pipe's radius. To test this idea, we'll show that you need sixteen tubes to pass as much water as one tube with twice their diameter.

We have two tanks of equal dimension next to each other. The first tank has a row of 16 tubes inserted near the bottom, all of equal length, and are 0.101" in diameter. The second tank has a single tube inserted with nearly twice the diameter (0.207") and equal length as the others. An equal amount of water is added to the tanks, so that the pressure difference between the ends of all 17 tubes is the same. With the fluid viscosity, pipe length, and pressure difference the same among all the tubes, the only difference is their radii.

The valves to all the tubes are opened simultaneously, and we see that the flow rates are very nearly equal--even over the course of several minutes. (The difference in water levels seen at the end of the experiment was measured to be roughly 5 percent.)

For more details on our setup, see https://sciencedemonstrations.fas.har...