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Anti-gravity globe question

  1. Aug 30, 2009 #1
    "anti-gravity globe" question

    I had a question about the anti-gravity globes, and used to wonder if they would still work if flipped upside down, I now realize they won't when I actually thought about it.

    However, is there anyway to suspend an object using magnets with the base on top? I looked on google for a little while and didn't find anything. I've lurked here for a few months and figured this would be the best place to ask.

    the globe I'm talking about http://www.thinkgeek.com/geektoys/science/98b8/?cpg=ab

    Sorry if this is the wrong section
     
  2. jcsd
  3. Aug 31, 2009 #2
    Re: "anti-gravity globe" question

    What do you mean with "tha base on top"? It will depend on the desing of the gadget.

    I can imagine what you're thinking and I guess it's possible but please try to make yourself a little bit more clear so that I may help you :)
     
  4. Aug 31, 2009 #3

    D H

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    Re: "anti-gravity globe" question

    I assume you mean that the globe is suspended below magnet rather than above it. To be stable the forces must balance at the suspension point and any small deviations by the globe from this point must be countered by a restoring force. This latter presents a difficulty with inverted orientation. The problem is similar to that encountered in trying to balance a broomstick (or inverted pendulum). The balance point is metastable. The greater the separation between the magnets, the weaker magnetic field gets, and vice versa. A constant strength magnet in the base will not do the trick. The globe will either fall to the floor or rise up to the magnet.

    The obvious solution is to use a non-constant strength magnet. Use an electromagnet with a controllable current flow. Reduce / increase the current if the globe gets too close to / too far from the magnet. This in turn means the device needs to sense the distance between the globe and the magnet and feed this back to the current control.
     
  5. Aug 31, 2009 #4
    Re: "anti-gravity globe" question

    Sorry about that zaphys. I was picturing a lightbulb suspended about an inch below the ceiling with the "base" above the drywall. So when you looked at it all you would see if just a hanging lightbulb. After that I'd want to wirelessly transfer energy to it. It would just be one lightbulb, because I know how inefficient it still is.


    And D H, I understand what you're saying, the globe I linked says it uses microprocessors to constantly judge where the globe is and adjust the magnet, so I would need to do something along those lines?
     
  6. Aug 31, 2009 #5
    Re: "anti-gravity globe" question

    Seems very likely.

    The
    in the illustrated orientation adds to the stability/orientation of the globe and that stability and location relative to the base is reflected in the software control.

    So inverting the contraption would now place the magnet next to the base to keep north up; likely control software would have to be modified.



    How would you in theory light a freely suspended bulb? That requires a complete circuit and offhand I can't think of a way to accomplish that....
     
  7. Aug 31, 2009 #6
    Re: "anti-gravity globe" question

    How about by electromagnetic induction?The bulb filament could act like the secondary of a transformer.It would be very inefficient and difficult to do in practise but in principle it would work.
     
  8. Aug 31, 2009 #7
    Re: "anti-gravity globe" question

    Am unsure exactly sure just how 'electromagnetic induction" works...but there seems no way for current to flow...as in a closed circuit...for conventional heating....

    I checked out Wikiepedia on microwave ovens since if you heat something enough it will get hot enough to emit electromagnetic radiation...maybe visible light. Wiki sez:

    I guess such metals do get hot in microwave ovens...but unsure just how....I checked tungston,too, and it sure has a LOT of applications I never considered..'''.but am unsure if it's molecules are dipoles....
     
  9. Aug 31, 2009 #8
    Re: "anti-gravity globe" question

    Occurred to me resistive heating might work ok via induction...looked up joule heating in wiki and it says:

    Sounds like it....anybody have better insights??
     
  10. Aug 31, 2009 #9
    Re: "anti-gravity globe" question

    I'll have to look further into wireless energy transfer to get more specifics on it, at the moment though I'm just exhausted from a LONG day at school. First days of the semester suck.

    I understand that the efficiency would be a joke, I'm certainly not looking to do this on a wide scale in my house or anything like that, I just thing it would be pretty awesome looking to have an "Edison era" light bulb suspended by the ceiling with no wires being lit up.

    But thanks for the advice on the possibility of the bulb being suspended, without that I didn't need to really research any further into my little project.
     
  11. Sep 2, 2009 #10
    Re: "anti-gravity globe" question

    Dadface posted:
    I forgot to mention that Wiki also discusses the relative (in)efficiency of microwave (ovens)...(electromagnetic induction) so if anyone is interested in thos losses you can get an idea there.....
     
  12. Sep 2, 2009 #11

    mgb_phys

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    Re: "anti-gravity globe" question

    The efficency of near-field resonant induction is quite good. If you can have a transmitter larger than the gap to the bulb (which you can put in the ceiling) an can control the position and distance to the bulb the efficiency isn't a problem.

    The stability of the system is trickier. By having a globe levitated over a magnet as the globe falls it moves into a stronger field and is lifted up - so naturally stable - even then you need software control to stop the globe moving out of the field sideways. Hanging below the magnet you would need to control the power - so that if the bulb moved down (away from the magnet) you could sense this and increase the field to lift it back up.
     
  13. Sep 4, 2009 #12
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