A solid iron cylinder (d = 5 cm, L = unknown, SG is on the sheets) is falling inside a tube with constant velocity 9.77 m/s. The gap is 1 mm, it is filled with lubricant oil. What is the oil viscosity (in Pa·s)?
Hints:
1) Express Volume-of-cyl and Contact-area with d and L of the cylinder
2) Express gravity force
3) Compute shear rate as we did in the case of standing and moving plates.
4) Express shear force (contact area multiplied by viscosity and shear rate)
5) Since the two forces are equal, you can solve for the unknown viscosity (the L should drop out).