what the capacitor??

Discussion in 'The Projects Forum' started by dameyawn, May 29, 2008.

  1. dameyawn

    Thread Starter New Member

    May 29, 2008
    so you know the basic experiment where you oppositely charge some plates set vertically and dangle an aluminum ball attached by string between them? the ball basically gains charge from one side, becomes attracted to the other, and starts bouncing back and forth.

    a friend of mine demonstrated this, and i suggested setting it horizontally, so we could watch balls bounce up and down endlessly. after surrounding the charged plates so the balls couldn't escape, we started throwing them in. as expected, they bounced crazily.

    then we started making different shapes out of the foil. most of them bounced sporadically. BUT THEN, something crazy happened. i had wrapped an aluminum foil strip around a small cylinder to make a spiral shape. the length of the spiral cylinder was about half the width of the plates(1.5 inches ish). first it bounced around and then very quickly, started moving more regularly. it started spinning, very wobbly, and moving in between the plates up and down without touchhing them. then after a few moments, it appeared to be spinning very rapidly, was fully upright and essentiallly levitating in place between the plates(in the middle). STEADY STATE!!! you could also see arcing between the plates and the bottom and top ends.

    what induced the spin? first i assumed it was a mechanical phenomenon, but then i made a heavier top-like shape. this moved randomly, then stabilized as well, spinning, and remained upright resting on the bottom plate. it was axial symmetric(unlike the spiral) but spinning was still induced.

    anyone have any idea what is causing this phenomenon? it looks awesome, so i recommend trying it. i will take some pictures/video soon and post it online to show what i'm talking about. i'm just really curious about why this is happening.
  2. mik3

    Senior Member

    Feb 4, 2008
    You apply a DC voltage across the plates, right?
  3. Caveman

    Active Member

    Apr 15, 2008
    That is fantastic! I've done the original experiment. I'm impressed by your inventiveness on altering the experiment. I'm looking forward to your picture/video posts. What is your voltage?

    One interesting theory about levitation is Earnshaw's theorem that states that no static arrangement of electrical, magnetic, and gravitational fields can be used to stably levitate an object. There are a few ways to get around it, though. Spinning is one of them.

    This is off-topic, but I only know of one non-powered magnetic-type levitator arrangement and it involves materials with strong diamagnetic properties. Here is a link to the one I own: http://www.kjmagnetics.com/proddetail.asp?prod=LEV2,
    but there are plenty of online sources to build your own.
  4. dameyawn

    Thread Starter New Member

    May 29, 2008
    DC, 7kV

    What I'm thinking so far:

    At first, the spiral is bouncing around(for the record, I don't think the fact that it is actually a spiral has anything to do with it. It was just hard to tell if a straight rod did the same thing.) So say it becomes positively charged, then bounces towards the negative plate. When one end touches the negative plate first, there is a potential and a current flow. This current incidentally creates a magnetic field, and because the foil spiral is "free," it spins in response to the field.

    Spinning induces angular momentum which tends to keep the foil aligned in the axis of the rotation. This begins to stabilize the spiral. When it returns to the positive plate, the same thing happens(current goes in same direction), and the spiral spins more. It is at its wobbling state (aka precession?).

    In a few moments, the spiral becomes fully upright and appears to be spinning more rapidly, levitating between the plates. So there is continuous current and a continuous magnetic field which serve to maintain each other - not to mention the conversation of angular momentum, which put and holds the spiral upright, in addition to the electric field force.

    I expect that measuring the angular velocity and using it with the capacitor specs, I might be able to relate them using some common formulas.
  5. dameyawn

    Thread Starter New Member

    May 29, 2008