1. Feb 28, 2004

galaphy

I seem remember somewhere there was a thread last year to discuss about what happens inside a rotating cylinder. It's to say if the obsever inside a rotating cylinder(big enough) can find out the motion state of the rotating cyclinder by experiments inside it.
I would rather say no, just like the observer inside the accelerating cabin cannot find if the cabin is accelerating or in a gravitation field. This is what the Equivalent Principle say. Now I find it's really very important to talk about this question as it deals with an Equivalent Principle between spin and magnetism.
Could anyone give me the link to this former thread?(I could hardly remember if I found it somewhere else)
Thanks

2. Feb 28, 2004

Creator

I believe I was the original author of that thread (wherever it is); it had to do with the relationship of Equivalence Principle, spin and angular momentum.

What are your ideas relating spin and magnetism with regards to rotation inside a cylinder?

Creator

Last edited: Feb 28, 2004
3. Feb 29, 2004

galaphy

Re: Re: About rotating reference system

Great, Creator, Where did you put your thread? I want to read all the discussions about it. I cannot find it now. Sure, I know one may think that the observer can judge the rotation of the cyclinder by a spinning gyroscope or something like that, such as a free single pendulum. Is it right?
But by introducing a new kind of magnetic force, he won't be able to distinguish if the procession of the gyroscope or pendulum was caused by this force or by the rotation of the cylinder. This is actually the same in Einstein's acceleration cabin. This is my new thought about rotation. What do you think about it?

Last edited: Feb 29, 2004
4. Feb 29, 2004

EL

In fact it´s possible to differ between acceleration and gravitation. If the gravitational field is spherical (e.g. the Earth´s) it will also pull things in the cabin towards the centre and thereby show its existence. Thus the equivalent principle really only says something about local frames of reference (i.e. it only holds "point by point").

Last edited: Feb 29, 2004
5. Mar 1, 2004

turin

The point of Eintein's equivalence princple was to attribute gravitation to an inertial effect (or, in the Machian context, vice versa). So, in principle, the inertial effects of the rotation of a cylinder cannot be distinguished from the gravitational effects of a spinning source (or spinning universe).

6. Mar 1, 2004

EL

Excuse me but I didn´t really understand this. What do you mean by "in principle"?

7. Mar 1, 2004

turin

EL,
Let me start by saying that I wasn't in disagreement with you.

By "in principle" I meant, "assuming that an infinite, uniform, straight line of mass extended through the universe, and no other mass existed in the universe. Then, according to Mach's principle, a reference point that observes a spinning line of mass is equivalent to a reference point that is in a circular orbit around a stationary line of mass."

8. Mar 4, 2004

galaphy

Well, I can understand what you're saying. You're quite right at those points. But what I want to know about is if we can distinguish the rotation of the cyclinder and an equivalence magnetic field in side it when one thinks there is a magnetic force exert to the gyroscope or pendulum.

9. Mar 4, 2004

HallsofIvy

The "coriolis force" on something thrown from one side of the cylinder to another would distinguish it from a gravitational field wouldn't it? Of course, if you are talking about a REALLY huge cylinder, that might be miniscule.

10. Mar 4, 2004

turin

What is an "equivalence magnetic field?" If you are talking about a gravitomagnetic field, then, in the real universe filled with other mass and energy, my answer is, "yes, even a gravetomagnetic field can be distinguished from a rotating frame." It just raises the philosophical question of, "is the cylinder rotating, or the rest of the universe?"

11. Mar 4, 2004

LURCH

I think not, since Corriolis force effects things on Earth like weather systems and sattelite navigation.

Somebody double check me on this, but I think it is fairly self-evident that the effects of rotation within a rotating cylinder should be indistinguishable from those observed on the surface of a rotating body with equivilent gravitational influence. That is, if one stands on the equator of a planet with the same diameter as the rotating cylinder, and the planet is rotating at the same speed as that cylinder, but generating a gravitational "pull" of 1G, gyroscopes, pendulums, and all other experimentation should behave identically on the planet's surface or in the cylinder.

12. Mar 5, 2004

galaphy

OK, I'd say directly, the equivalent magnetic force isn't the gravitomagnetic force. The most interesting thing I found is that, with the coriolis force, a spinning gyroscope will circle a center when it moves inside the cylinder in the plane which is perpendicular to the rotating axis(one may be able to prove this with mathematics). this force is equivalent to the magnetic force a charge meets in a magnetci field. It's to say, I can not distinguish if the spinning gyroscope is moving in a equivalent magnetic field or inside a cylinder(large enough).

Last edited: Mar 5, 2004
13. Mar 5, 2004

turin

Galaphy,
I didn't follow what you were saying. Is the gyroscope charged? What does "circle a center" mean? What force is eq. to the mag. force? The Coriolis force isn't.

14. Mar 7, 2004

galaphy

No, the gyroscope isn't charged. It's neutral. The motion of a spinning gyroscope inside a rotating system is the same as the motion of a charge in a magnetic field(circumferential motion). So, the coriolis force to a spinning gyroscope inside a rotating system is equivalent to the magnetic force to a charge in a magnetic field. Then, if I think the gyroscope is a charge, I can't differ this coriolis force from the magnetic force.

Last edited: Mar 7, 2004
15. Mar 8, 2004

turin

Why do you think this?

16. Mar 9, 2004

galaphy

I had finsihed some experiment on this. And you may find this regularity in the motion of tornados or typhoons near the poles of the earth. Of course you have to take the pressures from the air flows into account.

17. Mar 9, 2004