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Physics Demo -- Jumping Ring

A solid metal ring is placed on an iron core whose base is wrapped in wire. When DC current is passed through the wire, a magnetic field is formed in the iron core. This sudden magnetic field induces a current in the metal ring, which in turn creates another magnetic field that opposes the original field. This causes the ring to briefly jump upwards.

If there is a cut in the ring, it cannot form current inside it, and thus will not jump.

When the ring is cooled in liquid nitrogen, the resistance of the metal is lowered, allowing more current to flow. This lets the ring jump higher. However, the magnetic field curves away at the top of the iron coil, meaning with DC power, the ring will never fly off the top.

When AC current is passed through the wire, the ring flies off the top of the iron core. This is due to the fact that the current lags the emf by 90 degrees in inductors (which is what we have here). This yields forces on the ring that are always pointing upwards, even as the current oscillates.

Comments (5)

The question imply that the nature behaves by certain principles. Such understanding is nurtured by educators. They pretend to "uncover" the inner activity by bringing analogies such as atomic grids and silly electrons.

I believe the illusions educators create are dangerous. They may be easy to understand but dogmatic. This is because it was scientists who invented the rules to help themselves explain the observed effects. When they confirm the correspondence between the observation and their proposed rule, they start calling it "law". Years later a dissonance is observed and the "law" is amended.

Besides the corner case amendments, we may see a totally new look at the things that makes the earlier "laws" only particular cases of more generic new "laws".

Posted almost 6 years by Anonymous User

The liquid nitrogen drops the temperature of the metal ring, causing it to drop to around 40-80 degrees kelvin. This is almost near the superconductivity temperature, as the temperature drops the particles start to slow down and if it does reach 0 kelvin it was stop completely. This allows less collisions which equals lower resistance. Look up the CBS Theory of Superconductivity.

Posted almost 6 years by Anonymous User

Why does nitrogen lower the resistance?

Posted almost 6 years by Anonymous User

I have a question about the “effect” of liquid nitrogen and AC current. Was the cut in the metal ring made in such a way as to prevent the contraction of metal to essentially close the cut, making a solid ring? In regards to the AC current causing the more dramatic effect, is this due to the properties of AC cycling back and forth? Let’s assume that your AC power source is operating at 60Hz. Does the switching effect AC has happen so swiftly that it is a multiplying effect, thus creating more “lift”?

Posted over 5 years by Anonymous

we could send helicopter like blimps into the air with such a device…. and have them jump from base to base… no use in carrying all that fuel with you on your journey to the CENTER OR YOUR OMNIVERSE

Posted over 5 years by Anonymous

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MIT Department of Physics Technical Services Group

MIT Department of Physics Technical Services Group

Category: Science | Updated over 1 year ago

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April 03, 2008 13:12
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