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Magnetic repulsion Hover Boards

  1. Aug 25, 2009 #1
    Hello, I'm New and was wondering about magnetic hover boards. I have seen articles about using batteries to reverse the polarity of 50lb. lift magnets and allowing them to repel metal objects such as a piece sheet metal. I know it's possible to reverse the polarity but can it be done with simple 9vl. batteries like they say?? Also if so can it be done with grade n50 magnets?
    Thankyou
     
  2. jcsd
  3. Aug 25, 2009 #2

    negitron

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    Magnets attract ferromagnetic metals regardless of polarity. They will repel diamagnetic materials, such as bismuth, but the effect is far weaker than ferromagnetism.
     
  4. Aug 25, 2009 #3
    So basically unless you can make a base of a diamagnetic material, it won't work?
     
  5. Aug 25, 2009 #4

    negitron

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    Right, and even then, the diamagnetic repulsion force is so weak it can't even overcome the weight of the magnets needed to create it.
     
  6. Aug 25, 2009 #5
  7. Aug 25, 2009 #6

    negitron

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    Fake, fake, fake.
     
  8. Aug 25, 2009 #7
    well you think if i could make a electromagnet using a piece of sheet metal and use that as a base on the floor, Plus using 150 pound lift magnets instead of 50lb lift, I could lift at least some plywood?
     
  9. Aug 25, 2009 #8

    Danger

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    Sorry, man, but those videos have to be among the worst pieces of crap that I've ever seen on the net. It's so obviously fake that I can't understand why you ever considered it as possible. Even without the blatant violations of physical laws, you should have caught on when he soldered the wires to the battery terminals. Nobody would ever do that, unless maybe for a bomb.
     
  10. Aug 25, 2009 #9

    negitron

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    Sure, if you face off two like-polarity magnets, you can get levitation; Maglev trains rely on this principle. However, getting it to be stable is a major engineering hurdle. Simply opposing two magnets where one is allowed to move freely results in the levitated magnet falling off, flipping over and becoming attracted and stuck to the lifting magnet because that's the lowest energy state of the system.
     
  11. Aug 25, 2009 #10
    those shoes are so fake it's hilarious. you'd need way more than 2, 50lb magnets to get you to float THAT high, if that's even possible by 'shoe levitation.'
     
  12. Aug 26, 2009 #11
    What about a coil of wire over a metal surface ? Applying alternating current to the coil will create a magnetic field, and won't the induced Eddy currents in the metal surface repel the coil and make it levitate ? (I remember seeing this on one of the electro-magnetism courses MIT has on youtube)
     
  13. Aug 26, 2009 #12
    What you describing is a bit like dropping a magnet inside a copper tube. The magnet does not levitate it is mearly slowed in its decent. Although by use a Fe-Nb-B magent it does take a long time in a 1m tube. I don't think the coil would levitate but maybe it would not fall quickly if correctly set up.
     
  14. Aug 26, 2009 #13
    The difference is that the magnet has a fixed magnetic field not strong enough so that the electromagnetic force can overcome gravity. In case of the coil however the magnetic field is proportional to the intensity of the curent. So if we create a high enough current it's possible that the magnetic repulsion will overcome gravity and the coil will levitate.
     
  15. Aug 26, 2009 #14

    negitron

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    Perhaps, but we're talking about impractically high current levels, particularly for something meant to be portable.
     
  16. Aug 26, 2009 #15
    I have calculated that 100 paralel wires, each with a current I passing through them, with length 1m, will generate a magnetic field strong enough to lift 1 kg up to 0.5 m ... if I is 700A, which is indeed absurdly high.
    I deduced this from the fact that mirror charges will appear when current is passing through the wires thus creating a simmetric system, only with the current travelling in the opossite direction. Then I used the expression for the electromagnetic force:

    [tex]F=\frac{\mu I^{2} l}{4 \pi h}[/tex]

    Where h is the height, l is the length of the individual wires, I is the current.
    Since we have 100 wires we get that

    [tex]100F = mg [/tex]

    Replacing F in this equation we find I = 700 A.
     
  17. Aug 26, 2009 #16

    Danger

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    Which you ain't gonna get from the 9V battery shown in the video...
     
  18. Aug 26, 2009 #17
    I never said the video was real, I also believe it to be fake. I'm just saying that it's possible ... barely. You'd need a really big transformer to get 700 A. The normal ones (for charging batteries) get saturated when a very high voltage or current is applied... and even those transformers are heavier than 1 kg (I'm reffering to the bigger, heavier ones), so levitating like this seems very very difficult and unlikely.
     
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