Can you arrange magnets and a compass in a way that..

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Offline Seany

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Can you arrange magnets and a compass in a way that even though you aren't doing anything, the needle on the compass constantly goes round 360 degrees in perpetual motion?

I'm assuming it isn't possible... But if it was, it could be used as some sort of energy creating thing!!
When made in a bigger scale..
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Offline Bored chemist

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« Reply #1 on: 29/03/2008 16:19:14 »
"But if it was, it could be used as some sort of energy creating thing"
That's how you know it's not possible.
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Offline Seany

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« Reply #2 on: 29/03/2008 23:11:26 »
LOL otherwise we would be using that? Probably on car wheel axises or something
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lyner

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« Reply #3 on: 31/03/2008 23:02:01 »
Furthermore, you can't arrange a stable 'levitation' arrangement with permanent magnets - except, I have seen a toy which appeared to produce levitation but it relied on using a spinning magnet. Once the gyroscopic action died down through air friction, it flipped over and stopped working. Impressive whilst it lasted, tho.

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Offline Seany

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« Reply #4 on: 31/03/2008 23:03:42 »
That sounds really cool. Do you remember what it was called?
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lyner

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« Reply #5 on: 31/03/2008 23:14:40 »
Dunno but I have seen a movie on UTube. Search on magnetic levitation.

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Offline Seany

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« Reply #6 on: 31/03/2008 23:17:54 »
OK! Yayyy I'm all excited [;D]
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Offline Bored chemist

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« Reply #7 on: 01/04/2008 20:06:57 »
"Furthermore, you can't arrange a stable 'levitation' arrangement with permanent magnets "
You might not be able to but I have one on my table. It's not a big magnet, but it's stationary, floating in mid air and doesn't use any power.[attachment=2618]
« Last Edit: 01/04/2008 20:25:00 by Bored chemist »
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Offline Seany

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« Reply #8 on: 01/04/2008 20:37:42 »
Now that is very cool..

What's that pinky colour though?
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Offline Bored chemist

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« Reply #9 on: 01/04/2008 21:08:14 »
The colour is just a bit of red ink on the background so the magnet shows up nicely.
For scale, the gap in which the magnet is floating is quarter of an inch (6.3mm)and the disks are about 2 inches (5 cm) in diameter
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Offline Seany

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« Reply #10 on: 01/04/2008 22:23:23 »
What happens if you shake this?
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Offline Seany

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« Reply #11 on: 01/04/2008 22:24:21 »
« Last Edit: 01/04/2008 22:26:33 by Seany »
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Offline Seany

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Offline Bored chemist

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« Reply #13 on: 02/04/2008 06:52:51 »
"What happens if you shake this?"
If you shake it gently the little magnet acts like it's held on springs.
If you aren't gentle you find out that my woodworking skills are not up to much.
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Offline Seany

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« Reply #14 on: 02/04/2008 12:15:32 »
"What happens if you shake this?"
If you shake it gently the little magnet acts like it's held on springs.
If you aren't gentle you find out that my woodworking skills are not up to much.

Wow, did you make it?
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Offline Bored chemist

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« Reply #15 on: 02/04/2008 18:39:54 »
Well, I bought the magnets, the wood, the bit of brass tube, etc. but I made it in the sense that I put it together..
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Offline Seany

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« Reply #16 on: 02/04/2008 20:01:57 »
That is very cool.. What kind of magnets are they? Bar?
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Offline Bored chemist

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« Reply #17 on: 02/04/2008 20:57:48 »
What you can't see in the picture is the long (about 21") stack of cylindrical NIB magnets held together with a brass tube. The magnets are 5/8 long by 1/4 diameter so I must have used about 35 or so. These provide most of the force that holds that little magnet up. They were an eBay purchase.
The two disks that permit me to ignore Earnshaw's theorem are bismuth, cast in the bottom of an upturned soft drink can. They are held apart by a "C" shaped piece of perspex cut from 1/4" sheet.


I don't pretend to understand all of this
http://en.wikipedia.org/wiki/Earnshaw%27s_theorem
but I know that he must have not known about diamagnetic materials. Strictly speaking there are moving parts to this but they are electrons.
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lyner

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« Reply #18 on: 03/04/2008 10:47:31 »
That's really interesting; yes, Earnshaw only talks of  ferromagnetism. I didn't think about diamagnetism - just accepted his results.

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Offline Seany

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« Reply #19 on: 03/04/2008 11:24:14 »
So overall..

I can't arrange magnets and a compass in a way that the needle goes around and around in perpetual motion?
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lyner

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« Reply #20 on: 03/04/2008 13:03:32 »
Correct - that would imply perpetual motion and it is not allowed!

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Offline Seany

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« Reply #21 on: 03/04/2008 13:43:07 »
There can not be perpetual motion.. in anything?
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lyner

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« Reply #22 on: 03/04/2008 19:46:43 »
Any mechanism has energy losses (friction, resistance) which wastes some energy. It will run down. You can't get around it by gearing, levers or any other fancy ruse, either. It's fundamental.

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Offline Seany

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« Reply #23 on: 03/04/2008 21:00:13 »
But some sort of levitation maybe... Like "Levitron"
But then there would be air resistance?
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Offline Madidus_Scientia

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« Reply #24 on: 04/04/2008 15:54:16 »
Perpetual motion is possible, but not perpetual energy. Newton's first law of motion states "An object will stay at rest or continue at a constant velocity unless acted upon by an external unbalanced force". A comet speeding through space for example, will move perpetually (unless acted on by another force, like crashing into a star). If you could hypothetically make your compass and magnets arrangement completely frictionless with no resistance in any of the mechanisms, then yes the needle could spin forever. however, you could not generate power from this, because to do so you would have to induce a resistance on the motion.

And yes, although hard to balance, permanent levitation should be achievable, but it would be very hard. (like trying to balance a pencil on its point). If the magnetic fields that oppose gravity exactly cancel it out, there will be a net movement of 0.
« Last Edit: 04/04/2008 15:57:33 by Madidus_Scientia »

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lyner

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« Reply #25 on: 04/04/2008 19:53:44 »
Quote
permanent levitation should be achievable
Bored Chemist has achieved that. Nothing different, in principle between that and a mass hanging on a spring (although very ingenious, BC - respect).

There is always some interaction with other matter and some finite Kinetic Energy will always be transferred from even your moving deep deep space object. So, there will not be perpetual motion - however long the motion lasts for.
Where there is motion there is KE  but where there is equilibrium there is not necessarily KE so there is no work done and so there is no loss of energy; no principle is violated. So perpetual levitation is quite ok as a thought experiment.
« Last Edit: 04/04/2008 19:55:36 by sophiecentaur »

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Offline Bored chemist

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« Reply #26 on: 05/04/2008 01:32:14 »
I can take credit for the implementation, but not the idea.
I saw that someone had dome this and I basically copied it because I thought it looked really neat.
"So perpetual levitation is quite OK as a thought experiment."
Did you mean perpetual motion?
Incidentally there's some evidence that energy will be lost as "gravity waves"
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lyner

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« Reply #27 on: 06/04/2008 18:40:43 »
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Did you mean perpetual motion?
No, I meant what I said. Perpetual motion involves energy transfer - involving loss.
Levitation (static) involves no transfer of energy so I reckon it involves no loss - even by gravity waves, which (?) radiate when there is a change in GPE.

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Offline Bored chemist

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« Reply #28 on: 06/04/2008 19:56:41 »
In that case, never mind it being a thought experiment, I have got two on the table. The complicated one with the magnets pictured earlier, and the much more common type. There's a book on the table mysteriously held up in spite of gravity. Most people would just say it's resting on the table. I think it's the exclusion principle.
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lyner

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« Reply #29 on: 06/04/2008 21:31:31 »
Har har. I'll exclude you from my Christmas card list, matey.