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in the following picture, we should find the viscosity of fluid and we have to have the Area surface of cylinder that is in touch with the fluid. the area surface depends on the bottom of the shape. but i have no idea what's the shape of this cylinder. what is that curve on the bottom of cylinder? does it mean that cylinder is empty inside or what? enter image description here

and the solution of this problem:

enter image description here

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  • $\begingroup$ It is labelled « cylinder » so circular ... and the solution shows the view from the top... $\endgroup$ – Solar Mike Apr 8 '18 at 8:45
  • $\begingroup$ i meant the bottom of cylinder. i know what top of it looks like. the bottom of it may shows that it's empty inside. or maybe it shows it's curved. @SolarMike $\endgroup$ – user14854 Apr 8 '18 at 8:49
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There is no info about the shape of that curve in your, ie the book's, question, also, the torque shearing stress is calculated for the gap between the wall and cylinder which is small and much smaller than the gap between the base and the end of the cylinder.

Edit: After a re-read, the question does also say neglect end effects.

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  • $\begingroup$ why didn't he calculate the torque shearing stress between base and the end of the cylinder? $\endgroup$ – user14854 Apr 8 '18 at 9:26
  • $\begingroup$ As I put in my answer, the gap is much larger... from the solution given the difference between the larger and smaller radius is used... $\endgroup$ – Solar Mike Apr 8 '18 at 9:47

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