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Magnet question

  1. May 3, 2012 #1
    I don't have a physics background but a debunking to this irrational thought process of mine would be much appreciated. I understand perpetual motion/energy is an old, dried, and silly topic, but I can't make sense of this, so thank you in advance for answering (and yes, it's to do with magnets).

    This hypothesis doesn't rely entirely on perpetual motion, but consists primarily of it. I'm sure there's something basic I don't understand.


    There are two mega-magnets with incredible magnetic pull, and an extremely focused, narrow scope (capable of pulling specific objects from within earth's atmosphere from outer space). For the example imagine two identical mega magnets, M1 & M2.

    M1 is positioned on earth's surface, M2 is orbiting in outer space with just enough fuel to always keep it at an exact parallel with M1, but in outer space. For the example consider both magnets have the pulling power to pull a heavy object of equal distance to one another.

    There is a giant spaceshuttle made of ferromagnetic material, sufficient enough in quantity to be attracted to either magnet if the other didn't exist (ie: if the shuttle was in the position of M1, but M1 didn't exist, M2 could pull it to itself, and vice versa).

    Consider a scenario where M1 is built in such a way that it's based deep in the earth, with a giant non-ferromagnetic door that is capable of blocking the magnetic attraction. This door is capable of opening and closing independently of the magnet (using traditional power/electricity), and serves simply to block M1's pull. The same situation exists for M2 somehow (let's say instead of outer space it's based deep within the moon with the same door complex).

    In order to move the shuttle from the surface of the earth into outer space expending no fuel from the shuttle, would one not just need to close the door on M1's side, eliminating its magnetic influence on the shuttle and allowing M2 to pull? And when it's time to land, to put the door over M2 and allow M1 to pull?

  2. jcsd
  3. May 3, 2012 #2
    One problem with your scenario is that magnetic pull goes both ways. If a magnet in space can pull the shuttle UP, the shuttle will, at the same time, be pulling the magnet DOWN. This is covered by Newton's Third law, which applies to attractions as much as it does to collisions.
    As much as the shuttle is attracted to the magnet, the magnet will be attracted to the shuttle.
  4. May 3, 2012 #3


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    If I'm not mistaken, you cannot "focus" the magnetic field in such a manner either.
  5. May 5, 2012 #4
    I had a nice 2 page write-up where I did all the math proving that this wouldn't be effective at all, comparing the energy uses to that of the shuttle et al. Also considering various outfits for M2 the satellite electromagnet, but when I submitted it, PF asked me to "please log in" and lost the whole post. So here is a little diagram that was part of it showing the work required to lift an object, provided you have a 100% efficient conversion through the different "types" of energy (which you never do). I do have a few of the final numbers written down, one of which was for the orbiting satellite to simply power the magnet (100% efficiency) it would require a solar array of 8 square miles, at 10-15% efficiency per cell.


    What a bummer, I was proud of that post, and spent the better part of an hour writing it.
  6. May 5, 2012 #5


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    You cannot extract 'work' from a permanent magnet. It is a static field. You can temporarily get 'work' from a static field, like gravity, but, it is strictly temporary without an external energy source.
  7. May 5, 2012 #6
    If you could shield a permanent magnet without using energy, then you could have perpetual motion. Think about how electromagnets are used. They simply turn on and off at certain times, and can be used as an engine, to propel a roller coaster etc. If you shielded and unshielded a permanent magnet you could do the same thing.

    But, it would take energy to shield the magnetic field. Whatever it is you use to shield the magnetic field, would need to repel the magnetic field which would be a force acting on both the magnet and the shield.
  8. May 5, 2012 #7
    His magnets are permanent magnets, though. He turns them on or off by means of a fictional non-ferromagnetic door that can block the magnetic field. No such material exists, which is another thing wrong with the scenario.
  9. May 7, 2012 #8


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    There is no known material that can completely shield anything from a magnetic, or gravitational field.
  10. May 13, 2012 #9
    but you can distort the field with a ferromagnet, yes? that can do it to some effect
  11. May 13, 2012 #10


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    That is an unrelated effect to what is being discussed.
  12. May 13, 2012 #11
    You can shield a magnet with a superconductor, but not for free.
    Last edited: May 13, 2012
  13. May 14, 2012 #12
    What about hard drive magnets? they are shielded on one side,disassemble one and check it out.
  14. May 14, 2012 #13
    In theory, a superconductor could exist at room temperature. Unfortunately, such a material has never been observed.
  15. May 14, 2012 #14
    Here's an interesting article about magnetic cloaking.

  16. May 14, 2012 #15


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    Is that shielding for magnetic fields, or from EM radiation?
  17. May 14, 2012 #16
    Its a shield for a magnetic field,if you take a hard drive apart you will see the neodymium magnet is super strong on one side and the otherside with the piece of metal on it has no magnetism at all. Don't ask me how it works I would like to know myself?
  18. May 15, 2012 #17
    Those magnets are magnetized in two places, toward the ends. The poles are switched. Hold it with the magnet side facing you and you will have a North pole at one end, a South at the other. There is a corresponding South and North pole on the other side of the magnet where the "shield" is. The magnetic flux on that side is confined to the metal. I've pried the metal off on several of them and confirmed the magnetization pattern with a compass.
    Last edited: May 15, 2012
  19. May 15, 2012 #18
    mmmm!very interesting. I will check it out when I'm feeling a bit better, I just broke a bone in my foot aaaaagh!
  20. May 15, 2012 #19
    Wow. Better get that taken care of.
  21. May 15, 2012 #20
    Ive taken a painkiller an anti inflammatory and Ive got my foot elevated on a cushion, I wont be using magnets to try and cure it that for sure.LOL
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