Perpetual Motion!

[JamesNBarnes]

With most perpetual motion ideas its immediately obvious why it won't work (beyond the fact that it would violate the laws of thermo dynamics). Energy lost to friction for example. .

 

I know that I'm missing something here, but I don't know what.

 

I was reading about mri machines and was intrigued to see that they use super conducting magnets and once the coil is magnatised a super conducting bridge is dropped down and the coil remains magnatised by the perpetually circulating current.

 

Now, imagine two such magnets with the current being shifted between the two coils, via super conducting wire.

 

Surely, then you could have an alternating magnetic field that does not diminish over time?

 

Chuck a lump of iron between the two magnets and it will move... Free energy!

 

What have I over looked?

 

(I have made the assumption that iron being attracted to a magnet does not sap energy from the system. Probably wrongly. )

 

J

[Fuzzwood]

Chuck a lump of iron between the two magnets and it will move... Free energy! <-- That. This does sap energy from the system

[TonyMcC]

You would need materials that can be superconductors at room temperature - otherwise the necessary drop in temperature will require an input energy.

Iron subject to a changing magnetic field gets currents (eddy currents) induced within it which will sap energy by producing heat.

If you want to use the movement of a lump of iron it would be in some sort of guide or restraint which will introduce losses such as friction and air resistance .

[JamesNBarnes]

I realise that just moving iron around doesnt produce useful energy in its self, but once you have something moving requiring no input energy, you can hook it up to a reciprocating arm or some such. The method of extracting energy from the system is not what i was concerned with.

 

From my understanding, once the super conducting coil has reached superconducting temerature, very little further cooling is required they are well insulated.

 

What you mentioned about the eddy currents is something like i was expecting.

 

Lets say our lump of iron is a 10KG block moved vertically 1m.

 

Is the heat generated equal to the amount of potential energy gained? (thus cooling would require more energy than that which was gained from the increase in potential energy?)

 

To clarify:

 

Do the coils get hotter as they attract a mass?

Edited September 25, 2011 by JamesNBarnes

[John Cuthber]

The changing electrical and magnetic fields would act as a radio transmitter.

It would lose energy that way (if no other).

[JamesNBarnes]

The changing electrical and magnetic fields would act as a radio transmitter.

It would lose energy that way (if no other).

 

In what proportion to the amount of potential energy gained by the block?

[John Cuthber]

It's impossible to say without a better defined problem. The point remains that it doesn't matter. There's only so much energy you can get from the block and, at best, that's the energy you put into it in he first place.

If any is lost to the emission of radiation (and it will be) then you have wasted your time.

[JamesNBarnes]

My point was that the super conducting electro magnets to not require a constant current to maintain a magnetic field. They are hugely powerful and could generate a MASSIVE amount of force pulling in a solid lump of iron.

 

If the magnet was a permanent magnet then the metal block is now stuck unless you spend an equal amount of force pulling it back away from the magnet.

 

However with a super conducting magnet and wires if you were to bleed off the current to another coil (or a "holding" circuit) you could pull the block back to its starting position and do it over again.

 

No energy is lost in resistance. If a magnet lifts a 10KG block, where does that energy come from?

[John Cuthber]

"where does that energy come from? "

The electricity that they put n the magnet in the first place.

Also, when you move that big lump of magnetised metal near the coil you change the current in it (and the inductance) so you reduce the stored energy

[TonyMcC]

You could make a more simple version of your idea by using one coil connected to a capacitor which would set up resonance and if you could make the components "perfect and without loss" you could feed in some energy and the circuit would resonate for ever. In this state you would have an everlasting a.c. current at the circuits resonant frequency. The energy in the circuit would continually be transferred from the coil to the capacitor and back again. However, if you used any device to extract energy from the circuit then the energy held in the circuit would reduce by the same amount. This is known as "damping". The energy held in the circuit would bleed away to nothing. In practice, of course, there are losses and a resonant tuned circuit will be damped by those losses even if you are not deliberately using the stored energy. Therefore you will always get less energy from such a system than you put into it to get it started.

[Cap'n Refsmmat]

Yes, you use up some of the magnet's energy (in the current circulating in it) to exert a force on any magnetic material nearby. You could use the magnet to run a generator, but it would get weaker and weaker until it stops, and it'd give you just as much energy as you put in.

[JamesNBarnes]

Hmm, in that case, lets say i have a permanent magnet.

 

I use the magnet to pick up a nail. With the nail attached is the magnet less magnetic?

 

Edit: Also, lets say I do the same thing on the moon, gravity is less so the magnet does not have to do so much work, yet the mass of the nail remains the same. So would the magnet become less magnetic in proportion the the nail's weight or mass?

Edited September 26, 2011 by JamesNBarnes

[John Cuthber]

"With the nail attached is the magnet less magnetic?"

yes.

If you get a horseshoe magnet and lower it towards a paperclip on the table you can measure the height at which the clip jumps up to the magnet.

If you put a nail across the poles of the magnet and repeat the experiment you will find the magnet has to be nearer to the clip to pick it up.

[Marqq]

'Tis a noble pipe-dream (perpetual motion), but this convo made me wonder: In an MRI, how, if at all, is all that magnetic energy reclaimed? Is there a system like that for wind generators, returning the current to the electric company, or is it all stored in a battery within the machine, or perhaps it's just dumped down a ground line?

 

And to be more on topic: Does not any magnet, electric or otherwise, continually lose energy anyway in the form of the light (or non-light?)..well, EM radiation that it produces? I'm not sure how different the rate would be, as it always only produces the radiation, and the radiation itself is responsible for any effect beyond that. I'd love a link that explains this process...

 

Finally, the closest I think we'll get to perpetual motion/unlimited energy: Thermal energy!!! Every molecule in the universe is in constant motion...some would call it perpetual. This fact is so persistent, it's widely considered impossible to reach absolute zero. Just find a way to charge your magnets with heat energy alone, and you'll have enough energy to last until the next ice age (which you brought on...incidentally).

[seriously disabled]

Actually I think our universe is the ultimate perpetual motion machine.

[Fuzzwood]

Based on what?

[seriously disabled]

Based on what?

 

Because it may be infinite in extent and it is always in motion, motion which is never exhausted.

[swansont]

Because it may be infinite in extent and it is always in motion, motion which is never exhausted.

 

Has not yet been exhausted. That's not the same thing.