Is there any other method except just using permanent magnets ? What are the advantages and disadvantages of using the various methods ?
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$\begingroup$ do you have a diagram for what you mean by "axial" ? $\endgroup$– anna vCommented May 21, 2019 at 11:47
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$\begingroup$ @annav I have added a diagram $\endgroup$– Diyanko BhowmikCommented May 21, 2019 at 11:55
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$\begingroup$ the magnetic field has to be axial, but the force generated is tangent . hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magfor.html . There is a cross product. $\endgroup$– anna vCommented May 21, 2019 at 12:08
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$\begingroup$ Is the part free floating (like in space), or attached to something? $\endgroup$– John AlexiouCommented May 21, 2019 at 13:01
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1$\begingroup$ I think this question has merit in a theoretical sense and should remain open.I mean the question about how to weight your head was very popular and highly rated and this one isn't that far off in concept here. $\endgroup$– John AlexiouCommented May 21, 2019 at 13:07
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2 Answers
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Blowing pressurized air at the outer edge of the rotating object will get it to spin relatively fast, a static charge has a weak effect on another charged object. There could be more ways to do this but those are the easiest to use.
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$\begingroup$ Sorry, I had forgotten to mention that the force is to applied axially. $\endgroup$ Commented May 21, 2019 at 10:53
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$\begingroup$ water turbines too are rotating due to the flow. Axially is a later edit $\endgroup$– anna vCommented May 21, 2019 at 11:42
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$\begingroup$ We used to accelerate bearings with compressed air - a very dangerous activity as the bearings can shatter... $\endgroup$– user207455Commented May 21, 2019 at 13:36
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One can place a charge near the base of the cylinder, it will polarize and attract the cylinder (https://en.wikipedia.org/wiki/Electrostatics#Electrostatic_induction). One can also use radiation pressure (https://en.wikipedia.org/wiki/Radiation_pressure).
answered May 21, 2019 at 12:27
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$\begingroup$ How can you keep the charge on the disc for a long time ? $\endgroup$ Commented Jun 3, 2019 at 8:43
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$\begingroup$ @DiyankoBhowmik : I don't quite understand your question. I did not offer to put a charge on the disk. I offered to place a charge near the disk, on the disk's axis. $\endgroup$ Commented Jun 4, 2019 at 1:37
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$\begingroup$ Okay, but how can that be done ? I had thought that you wanted to put a charge on the disk in some way. $\endgroup$ Commented Jun 4, 2019 at 17:07
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$\begingroup$ @DiyankoBhowmik : No, I did not write anywhere that the charge is put on the disk. I had the following picture in mind: a (small) charged object is placed near a base of the cylinder, at some distance from the base, on the axis of the cylinder. The charge will polarize the cylinder and will attract it. As the cylinder moves towards the charged object, one can move the latter away from the cylinder along the axis to prevent a contact between the charged object and the disk. $\endgroup$ Commented Jun 5, 2019 at 1:08