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A cool suspended globe I saw.

  1. Jun 4, 2004 #1


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    In my youth the local Sears store used an air hose blowing upward to suspend a beachball in the air, as an attention-getter for the part of the store where they sold vacuum cleaners. The ball jiggled around chaotically, but it stayed more-or-less above the snout of the air hose.

    Fast forward to yesterday...

    I was in a coin shop. On the counter there was a spinning globe representing the earth. It was about ten inches in diameter, and spun roughly once per second around a vertical axis. Here's the cool thing: it was not touching anything but air. It reminded me of the ball at Sears, except that its motion was much steadier. As near as my eyes could tell, the globe's axis remained steady as a rock while it spun. There was a metal arm that had a cone pointing down toward the north pole of the globe. A couple of inches of air separated this cone from the north pole. There was also a metal saucer about five inches in diameter on the desk top, with the south pole of the globe a couple of inches above it. I say "saucer" to give a rough impression of what that part looked like. Another description would be to say it looked like a reflector-telescope mirror might look if the curvature of the glass were exaggerated substantially.

    Does anybody know the operating principle? Or can you figure it out? I asked the proprietor if he knew how it worked, but he didn't. It was not for sale, it was just a gee-whiz type of thing that they had in the shop.

    All I can guess is that a magnetic field is involved in the process of suspending the globe. Maybe the field is rotated in some fashion by a hidden arrangement of coils, and thereby manages to keep the globe in lock-step somehow.
  2. jcsd
  3. Jun 5, 2004 #2
    Reminds me of this http://www.levitron.com/
    Always wanted to get one but could never find it.

    I've seen globes suspended in the air before using magnets but they didn't rotate steadily as you describe.
  4. Jun 5, 2004 #3


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    Okay, I had never heard of a Levitron before, but the globe probably works in a similar way. The "saucer" I was talking about looked kind of like the upper white part on the base of the machine shown on the home page you linked to. The suspended part of the Levitron is said to spin; it looks quite a bit smaller than the globe was. Also the Levitron spins "from about 20 to 35 revolutions per second," which is considerably faster than the globe. I guess if you reverse-engineered a Levitron, and then tweaked it here and there, you could wind up with the globe that I saw in the shop.
    Last edited: Jun 5, 2004
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