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Why doesn't magnet + gravity = energy?

  1. Jun 29, 2012 #1

    Please forgive my ignorance. I am not a mechanical engineer or physicist by degree or trade (I am a software engineer). I am well aware that perpetual motion is a violation of conservation, and that (even if it were not a violation) perpetual devices could not perform work.

    My question is about harnessing forces available. Why is it not possible to configure a system next to copper that, as an example, raises a magnet with a magnet, then lets the magnet fall with gravity? My (almost positively unoriginal) idea would be to have the magnet in motion welded to a gear system (or something; again, I am not knowledgeable on the subject) that, as the magnet moves, rotates a horizontal fan-like insulating component between the magnets. In the first phase, the magnet is at the bottom; in the second phase, the magnet has moved almost to the bottom of the fixed magnet (during motion, the insulating material is moved to block the field); in the third phase, the insulating material blocks the field completely, allowing the magnet to fall with gravity. Any balancing effect could be (I imagine, with my current understanding) circumvented with a feedback to a well-placed electromagnet...

    Again, I know it is not possible...but why? Thank you.
  2. jcsd
  3. Jun 29, 2012 #2
    If the magnet was strong enough to oppose gravity, and raise the other magnet, then how would the other magnet be able to fall back?
  4. Jun 29, 2012 #3
    Hello Dickfore,

    Thank you for replying. The work of the system is performed my the moving magnet (next to copper, producing alternating +- fields). The insulating material that moves between the magnets would hypothetically be what interrupts the attractive field. With no attractive field present, gravity would cause the lower magnet to settle back to the original position.

    Periods below are to create spacing (the forum apparently strips whitespace)


    ...................Insulating_Material (horizontal fan) ---|
    ...................++++++ (Some type of gear-belt system)

    1. Lower magnet at bottom; insulating material has gap
    2. Lower magnet moves up; lower magnet raising-lowering rotates insulating material
    3. Lower magnet is almost at top magnet; insulting material moves into position between
    4. Insulating material cuts field, causing lower magnet to fall

    Again, thank you very much.
  5. Jun 29, 2012 #4
    First of all, there are no magnetic insulators. Next, I really don't understand your statement that "the work of the system is performed by the moving magnet". Finally, what is this gear/belt system and what torques act on it. I really don't get your "diagram".
  6. Jun 29, 2012 #5
    Hello Dickfore,

    1) You do not need to be capable of understanding the diagram, as you have answered my question perfectly. If nothing can damper a magnetic field enough to allow gravity to overtake the bottom magnet, then the system could never work. As magnetism is exponential with relation to proximity, distance could not perform the role of an insulator.

    2) The work of a system is how the system produces useable energy (in this instance, electric energy from the magnet raising and lowering that creates [at any given point in the copper] a field that alternates twice per lift-fall cycle).

    3) The bottom magnet is fixed (e.g., jb welded) to a gearbox that translates the vertical movement of the magnet the the horizontal insulator. Again, it does not matter if there is not a magnetic insulator.

    I appreciate your assistance greatly; however, I already acknowledged that I am a novice. Please do not suppose you know my mind by adding sarcasm. Have you ever drawn a decent ascii diagram? I have expertise that outmatches yours, it is just not mechanical in nature. I would help you in earnest, without sarcasm and with humility, if you had a software development question. Again, thank you for answering my question.
  7. Jun 29, 2012 #6


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    DaphnesDaddy, you are clever enough to recognize several places where the device fails. Here is one more to consider:

    Your device is intended (if it worked, of course) to create a current (an output of useful energy) by moving the magnet past some copper, inducing current. Don't forget though, that to induce this current, the magnet experiences a drag. (You would feel this drag simply by holding a magnet in your hand and waving it across a conductive wire.) This drag is in addition to the force of gravity pulling the magnet down.
  8. Jun 29, 2012 #7
    Hello Dave,

    Thank you for responding. I am certain that the minds from which I borrow this concept would have imagined a workaround by now if one existed, but (for my amusement) is there anyway the drag (or anything) could be added in place of an insulator? The system of which I am thinking is totally reliant on something being able to interrupt the permanent magnetic field attraction.

    What if (as an example), instead of an insulator, the horizontal fan component were magnetic (with a like charge to the top of the bottom magnet...and tremendous gaps between blades)? The magnet would then raise by the attraction of the top magnet and lower with repulsion of the fan-like component. The rotation of the fan component is governed mechanically by the raising and lowering of the moving magnet, ensuring precise timing.

    This conversation is entirely for a thought experiment. The most I have ever built is a stirling engine, and I do not have anywhere near the expertise in this field necessary to make educated guesses. I would just like to know some of the basic ins-and-outs without paying for an engineering degree. Your comments are appreciated.
    Last edited: Jun 29, 2012
  9. Jun 29, 2012 #8


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    That way lies madness. The hallmark of PPMs is the never-ending attempts to ever more subtlely subvert the laws of thermodynamics.

    Alas, even as a thought experiment, discussion of PPMs is forbidden on PF.

    I do believe this thread is doomed - unless you care to change the course of the topic real soon.
  10. Jun 29, 2012 #9
    Hello Dave,

    I was unaware of the PPM rule. I will discontinue this thread. Before I go, though, I want to express my appreciation (it is good to know my crazy ideas are in good company). I genuinely thank you.
  11. Jun 30, 2012 #10
    1) Just a technical point, magnetic fields do not fall off exponentially, but approximately by a power law with distance.

    2) Now I think I understand the essenece of your concept. You want to support a periodic motion of 2 attracting objects (magnets), by introducing a feedback (gear and belt).

    However, in your belt link, you need to be aware of the need for extra torque to overcome the torque due to the magnet's attractive forces. If you look at a detailed diagram of your device, I am confident that you will find your belt does not satisfy your condition.

    3) You seem to want to use this relative motion of the magnets to induce emf in a coil. However, according to Lenz's Law, there will be a magnetic field due to the induced current in the coil that opposes this relative motion of the magnets. I guess you need gravity to give you this "extra push". If you go to the belt, you will find it does not work again.

    Notice that your machine wouldn't have worked even if you had a magnetic insulator.
  12. Jul 1, 2012 #11
    DD: neglecting any ideas as to how to produce energy your basic idea about a rotating fan-like 'insulator' to change the force between magnets has some merits.
    What you need is not an 'insulator' but a steel (or iron) plate. If you had a segmented steel plate spinning horizontally between the poles of 2 magnets then the force between them would change (actually because the iron is a sort of 'conductor' of magnetism).
    Wheter this changing force could be usefully used to produce useable energy..... I very much doubt it.
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