# Rotating disks

Discussion in 'Physics & Math' started by jaiii, Mar 2, 2014.

1. ### jaiiiRegistered Senior Member

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Good day.

If we have two discs in one plane, and each is rotated in the opposite direction.
What will be the resulting force discs?

Thank you

Goodbye.

3. ### originIn a democracy you deserve the leaders you elect.Valued Senior Member

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10,684
I don't see nearly enough information to answer this question. Why would there be any force? Are the discs connected to something or each other. What is the mass of the discs? What are the size of the discs? How fast are they rotating?

5. ### jaiiiRegistered Senior Member

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195
One disk generate centrifugal force and another disk generate centripetral force.
Disks are not join.
They are in the same plane and near each other.
Velocity disks are the same.Mass is also the same.
How will be gravity field between disks?

7. ### originIn a democracy you deserve the leaders you elect.Valued Senior Member

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Huh? Are you stating that there are 2 rotating disks and on of them has only centripetal forces and the othere has only centrifugal forces. How would that be possible?

Anyway AFAIK the gravitational forces are a result of the mass so the spin would have no effect. It may be under GR that the energy of the rotating discs must also be taken into account in which case the gravitational field would be infinitesimally higher than the field due to the mass only. Hopefully, a physicist (and not an pseudoscientist) will add to this thread.

8. ### Uncle PythagorasBannedBanned

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I think he means the Casimir effect with opposite spins added to it. Probably some sort of frictionless space effect.

9. ### originIn a democracy you deserve the leaders you elect.Valued Senior Member

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Maybe, at this point I am just guess as to what he is asking.:shrug:

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Well, whatever it is it sounds like nonsense to me. (Shrug)

11. ### brucepValued Senior Member

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A way to figure that out is to start by defining the contribution of the spinning discs to the local spacetime curvature [gravity]. In this case it's the mass of each disc including the contribution to the disc mass by the angular momentum of each spinning disc. Don't expect much since any difference between the discs being there or not being there is infinitesimal. You're standing on a scale and you measure your weight. Now move the discs into position and then measure your weight. Establish the rotation of the discs and measure your weight again. Would you expect to measure a difference in your weight over the three measurements? You have the mass of the earth and the mass of the discs contributing.

12. ### OnlyMeValued Senior Member

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Jaiii, if what you meant is two spinning disks separated in a similar way as the plates in the Casimir effect, I am not sure there is anyone here who could give you a really good answer. It would involve QED mathematics describing how the spin of the disks would affect the ZPF, associated with the effect. As long as the plates did not touch it would be an issue of how their spin affects the virtual particles (ZPF) around and between them.., and then how their opposite spins interact in that context. (There are a few people who post on these topics, like Alpha Numeric, that understand the math, but I suspect the issue raised in this context has not been widely examined in the past.)

As Origin pointed out the spin of the disks would have little impact on their overall gravitational interaction. I am not sure that even, if the two disks were spinning in the presence of frame-dragging from a third significant gravitating body the different spins would have a significant impact. The frame-dragging effect itself is so slight compared to the attractive force of gravitation that it would be difficult to even guess at an answer.

As to the original form of your question, if the disks were massive enough to be gravitationally significant they would both experience centrifugal and centripetal forces independent of one another. If they came into contact the result of the opposite spins could be described more accurately in terms of everyday mechanics. Two opposite spinning disks hitting each other.

But as mentioned by others you would need a great deal more information to reach any conclusion. Total mass, rate of rotation or spin, how far apart and in what orientation to each other.... And whether you are concerned with the mechanical forces, gravitation and its subtle frame-dragging component or how the two disks interact with the ZPF and through that with each other.

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Thank.

14. ### OnlyMeValued Senior Member

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Jaiii, I am sure that if the plates were spinning it would have some affect. I could not even begin to say exactly how it would change the Casimir effect as it is generally thought of.

Understanding that the following is entirely within the realm of speculation, if the disks were spinning the same direction they might transfer some centrifugal force or spinning to the associated ZPF between the plates and increase the Casimir effect, by reducing the virtual particle density even more than would be the case with stationary disks... But that is a wild and unsupported guess. With the plates spinning in opposite directions the mechanics of what affect that would have on the interaction between the plates and the ZPF are way too complex for my limited understanding of even the Casimir effect between stationary plates.

This is why I said there are few around here who could even begin to give you a really good answer. The math involved is very high level and requires a keen understanding of QED. The paper I linked in your other thread describes the Casimir effect with stationary plates. Add rotation and then opposing rotations and well I have not seen anywhere that the question you ask has even been raised let alone answered.

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16. ### jaiiiRegistered Senior Member

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Thank very much.

17. ### Uncle PythagorasBannedBanned

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Hey I think I figured this out by using black holes as an example. You get spins which translate into a total spin that rotates as a single body. So the outer edge, and inner middle all have the same rotation speed between the plates. I was looking at how information escapes from black holes, so one thing led to another. It's caused by all of the forces eliminating themselves from their surroundings. Information is therefore lost.