

Ask HN: using only static magnetism - impossible to stably levitate against gravity? - tocomment
http://en.wikipedia.org/wiki/Earnshaw%27s_theorem
I don't get it?  Why would something like below work:&#60;p&#62;&#60;pre&#62;&#60;code&#62;     ________
     SSSSSSSS
     NNNNNNNN
&#60;/code&#62;&#60;/pre&#62;
NNNNNNNNNNNNNNNNNN
SSSSSSSSSSSSSSSSSS&#60;p&#62;Top magnets are glued to a board, a larger area of magnets are glued to the floor.  Surely the magnets wouldn't have the strength to flip the board, so how is that not stable?
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jonshea
Earnshaw’s theorem applies to electrostatic fields (ie, from non-moving
charges) as well as magnetic fields. I think electrostatics are a bit easier
to visualize than magnetostatics.

There’s also a good analogous physical situation. Imagine you have a rubber
sheet stretched into a plane. The challenge is to create a local minimum in
the sheet by pushing it up in places. If you push it up with a tube to try to
create a bowl, instead you’ll get a flat circle on top of the tube.

My freshman year physics professor had us play with a program that simulated
kinetic physics for point charges. You could “glue” charges to a plane, and
then release other charges to see how they would respond. The end of the
assignment said “Try to create a cage that can hold a charged particle. If you
do, you might be eligible for a prize.”

~~~
tocomment
Any idea where I could find that program. I think that would help me. My
problem really is visualizing it.

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tocomment
I don't get it? Why would something like below not work:

    
    
            ________
            SSSSSSSS
            NNNNNNNN
    
        NNNNNNNNNNNNNNNNNNNN
        SSSSSSSSSSSSSSSSSSSS
    

Top magnets are glued to a board, a larger area of magnets are glued to the
floor. This would be in two dimensions. Surely the magnets wouldn't have the
strength to flip the board, so how is that not stable?

~~~
mtinkerhess
IANA physicist, but how could magnets be strong enough to lift the board off
the ground but not strong enough to flip it?

~~~
tocomment
I thought of that, but what about magnets barely strong enough to lift the
board, maybe 1cm or levitation or something?

~~~
mtinkerhess
Then wouldn't the board start to destabilize until an edge hit the ground? So
it wouldn't be floating exactly, just sort of eerily resting.

~~~
tocomment
True. Good point. What if you curved the bottom piece into a slight dish
shape?

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tocomment
I may just have to try it huh? Where can I buy a whole lot of cheap magnets?

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jellicle
For extra credit, explain why the Levitron DOES work:

<http://www.youtube.com/watch?v=05FDGCis-Sw>

(no camera tricks in that BTW, it's just a magnet top and a magnet bottom. The
weight in the top must be carefully adjusted in order for the device to work.
It will continue levitating for as long as the top keeps spinning fast enough
- if you carefully blow on the top's side to speed it up, you can keep it
levitating for many minutes.)

