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# Newton's Mag-Lev

Like the cradle, but with magnets
 (+3) [vote for, against]

The magnetic spheres would be hollow (possibly not necessary but better anyway to reduce mass) with the + poles pointing inwards.

The track would be magnetic with 2 strips of - ive facing up like rails, slightly stronger at the ends than the middle to return the balls with a force approximating gravity.

Is air resistance the only force that would cause it to eventually stop? If so, I propose a vacuum enclosed deluxe version with external priming magnetic wand to draw the ball back and release it.

 — marklar, Mar 20 2012

A related idea Bounce_20Stick
A central stick acts as the "rails" [Vernon, Mar 21 2012]

Meissner effect http://en.wikipedia...iki/Meissner_effect
Expulsion of a magnetic field from a superconductor [8th of 7, Mar 21 2012]

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//hollow ... with the + poles pointing inwards// You need a hole for the flux lines to escape through. That might spoil the levitating bit.
 — pocmloc, Mar 20 2012

 Yeah, I wasn't sure about that bit. If it proves to be a problem I think it would work if they were oblate spheroids (Earth shaped) with a pole at the poles and a pole at the equator.

I hereby name this kind of magnet a Satsuma Magnet.
 — marklar, Mar 20 2012

Balls O'Bismuth ?
 — FlyingToaster, Mar 20 2012

 Yeah, I think the spherical-pole-outward magnet is doomed - I wanted to do something similar, but was told firmly that the net flux through such a shell would be zero.

 However, I like the idea of a maglev Newton's cradle, which could be implemented in other ways.

 You could also do this on a circular track - one ball (or whatever it was) would whizz around the track, hit the back of stationary train of balls and knock one off the front, which would whizz around.... this would be pretty, because the group of stationary balls would "move" incrementally in the opposite direction to the moving balls.

Actually...hang on, another idea...
 — MaxwellBuchanan, Mar 20 2012

 When I was in school I spoke to my physics teacher about the spherical magnet configuration. My question was, what would happen if you made 2 hemispheres magnetised like this, and brought them together?

We ended up concluding that the potential energy of forcing the halves together would be large enough to remagnetise part of the shell in the other direction.
 — Wrongfellow, Mar 20 2012

If the maglev track was curved like a gentle "U" (and also vertical like a "U") then the normal situation would be for the balls to rest in the middle. We probably want the bottom to actually be level, so they don't move when one is pulled away from the others. Pull one far-enough away, and it starts up along one side of the "U". Now release.
 — Vernon, Mar 20 2012

What you may not be able to do with magnetism you might be able to do with a shaped air jet. The top of a desktop negative-ion machine or something.
 — FlyingToaster, Mar 20 2012

 Oh, yeah, google for "Earnshaw's theorem" for another reason why this won't work.

Maybe you can make it work if you make the spheres out of a diamagnetic material, though.
 — Wrongfellow, Mar 20 2012

 Failing all attempts to make the final toy look like an original Newton's cradle, you could make a scale mag- lev train where the carriages had magnetic buffers. However it's achieved, we all know that mag-lev trains exist so it must be possible, just maybe not in spherical form.

And I'm now starting to warm to the idea of it being a little crashy train set.
 — marklar, Mar 20 2012

 //Is air resistance the only force that would cause it to eventually stop?//

No. The collisions between (balls/train cars/whatever) will not be perfectly elastic. As such, each time they collide some of the energy is converted to heat. How much would depend on the materials and construction, but even highly rigid materials in a vacuum would still run down in an observable time frame.
 — MechE, Mar 20 2012

 As far as making the spheres, there is no reason you can't have a mag-lev track that handles spheres, as long as the magnets themselves aren't spherical. I think the following will work, if not some variation on it will.

Put two magnets inside the sphere, such that you have two stong north poles oriented down left and down right. Put a weak south pole magnet oriented straight down. Construct your U shaped track out of a series of north pole magnets. The weak center magnet will maintain orientation while the strong outer magnets levitate the object.
 — MechE, Mar 20 2012

 //The collisions between (balls/train cars/whatever) will not be perfectly elastic//

 [MechE] They will not collide, they will be repelled by magnetism. This will affect the alignment of molecules each time, bit by a miniscule amount.

 //Put two magnets inside the sphere,//

Instinctivly, I think the sphere will flip over, but I guess it's worth testing, it's simple enough to try.
 — marklar, Mar 21 2012

 //They will not collide, they will be repelled by magnetism//

I pictured it as collisions, but if it's magnetic, then eddy currents and similar produce the exact same effect. Regardless, the interactions are subject to the second law of thermodynamics, and energy will be lost each time.
 — MechE, Mar 21 2012

 — 8th of 7, Mar 21 2012

 I don't claim to understand the magnetic effects of superconductivity, but I believe that you would still lose energy during the interaction.

With regards to Earnshaw's theorem and the feasibility of doing this with permanent magnets, it appears to me to allow for tracks by aligning the required axis of instability with the direction of the track, but I may be wrong on that.
 — MechE, Mar 21 2012

 //       I don't claim to understand the magnetic effects of superconductivity, but I believe that you would still lose energy during the interaction.    //

Seconded, and no amount of fancy math is going to convince me otherwise. In my universe, you can't sidestep entropy. Persistent currents within the field may not decay, but magnetism is not the only fundamental force in play here.
 — Alterother, Mar 21 2012

I wasn't suggesting that it would go on forever, I was just hoping that it would continue for a decent amount of time, so as a desk toy you could start it in the morning and decide to take a coffee break when it stops, without dying of caffeine poisoning by lunchtime.
 — marklar, Mar 22 2012

Hmm. This certainly has the beginnings of a useful toy in it somewhere. Here, have an R&D bun. Don't spend it all at once. [+]
 — BunsenHoneydew, Apr 07 2012

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