Spin-stabilized magnetic levitation is a phenomenon of magnetic levitation whereby a spinning magnet or array of magnets (typically as a top) is levitated via magnetic forces above another magnet or array of magnets, and stabilised by gyroscopic effect due to a spin rate that is neither too fast, nor too slow to allow for a necessary precession.
The phenomenon was originally discovered through invention by Vermont inventor Roy M. Harrigan in the 1970s. On May 3, 1983 Harrigan received a United States patent for his original levitation device based upon this phenomenon he discovered.[1][2] Independent of Harrigan, a Pennsylvanian inventor named Joseph Chieffo made the same discovery in 1984 employing a flat base magnet, a geometry that proved a significant change over his predecessor's patented design which relies upon a dish shaped mounting of magnets for the base. Chieffo's design, publicized in a 1991 edition of the periodical "Magnets In Your Future",[3] further differed from Harrigan's in its incorporation of an un-weighted top.[4][5] Harrigan's technology, either solely or in conjunction with Chieffo's published flat-base variation, provided the basis for the development of mass marketed levitating toy tops sold under the brand name, 'Levitron'.
In 2012[6] and 2014[7] Max Michaelis reported operating Levitron brand magnetic tops at inclination angles of 45° and 90° (i.e. with the spin axis, horizontal) after employing novel configurations for the supporting magnetic fields.
YouTube Encyclopedic
-
1/1Views:34 022 882
-
Anti-Gravity Wheel?
Transcription
I am here at the University of Sydney where the mechanical engineering shop has built this incredible piece of apparatus for me. It is a forty pound, that is nineteen kilogram flywheel on the end of a meter long shaft. Can you imagine trying to hold this out horizontally with just one hand at this end? It is virtually... it is impossible, ok? No I'm going to let go. You going to be able to hold this at all? I hope so. Can you lift it out? Make it horizontal - hold it, hold it, hold it. Come on. Just try to - I want you to hold it out horizontal. See if you can. Hold it, hold it! Ahh, come on! No. What I'm going to do is I am going to spin this up to a few thousand RPM and then I'm going to attempt just that, to hold it from one end and have it out horizontally. Five, four, three, two, one. Boom. I'm going to let go with my left hand. What you'll see is that the shaft remains horizontal, see it going around there. It almost looks as though the wheel is weightless. How does this work? Well instead of pulling the wheel down to the ground as you'd expect, the weight of the wheel creates a torque which pushes it around in a circle. You may recognise this as gyroscopic precession. For a more detailed explanation, click the annotation, or the link in the description to see my video on the topic. Here I want to try something more extreme. I'm going to try to lift it over my head with one hand while it's spinning. Wish me luck. But before I make the attempt, Rod wisely suggests that I first check if I can lift the wheel above my head without it spinning. OK, let's prove that I could lift it, just this end, without it spinning. Here we go. agggh I mean it's just kind of awkward with the hand. Careful! Ah, che Careful! Ha Oooohhh Just barely. Oh goodness, do you even lift? Clearly I do not. Undaunted by my lack of strength, I'm going for it, but I want to make sure the wheel is spinning as fast as possible to give me the best chance of success. Give it ten more seconds. Ten, nine, eight, seven, six, five, four, three, two, one. Pull! Go. That was perfect. Now I'm going to release my left hand and holding only with my right hand at the end of the shaft, I'll try to lift it up over my head. This is a forty pound, nineteen kilogram flywheel. Ready? Here we go: three, two, one. Beautiful! Let's go again in three, two, one. Nice! Smooth. Three, two, one. It feels incredibly, incredibly light as I do that. When you said it felt incredibly light, yeah you mean when you're lifting it feels light? Yeah. It shouldn't! I know. Hahahaha Honestly, I have lifted it up with one hand when it's not spinning. Yeah. And it feels really hard to lift it up, like it's a big effort. Yeah. But with this, when it's spinning it honestly felt like it was just... wanting to go up by itself. Yes. It felt like I was not struggling like I was not putting in the amount of force that you'd think to lift that kind of weight. I bet if you let it go, it'd crash down to the ground. It's not weightless! We can't do that though. We can't do that part of the experiment. What we could maybe do is I could stand on a scale and we could see what the weight of me plus that apparatus does, while I'm lifting it up over my head, see if I get lighter in essence. You can see that just my weight is about 72 kilograms. Now when I pick up the flywheel it goes up to about 91 kilograms, which makes sense because the flywheel itself is about 19 kilos, that's about 42 pounds. Now we're going to spin it up and I want you to make a prediction. As I'm lifting it over my head, do you think the scale reading will be more, less than, or equal to 91 kilograms. What do you think? You can make your prediction by clicking on one of the on-screen annotations or if you're on mobile you can click a link in the description. Five, four, three, two, one.
Physics
Earnshaw's theorem does not allow for a static configuration of permanent magnets to stably levitate another permanent magnet or materials that are paramagnetic or ferromagnetic against gravity. This theorem does not apply to devices consisting of a properly configured magnetic base and corresponding magnetic top, however, because the non-static nature of the spinning magnetic top within a threshold of lower and upper RPM spin rates acts as a balanced precessing gyroscope to prevent the poles of its magnetic field from fully aligning themselves in the same direction as those of the primary supporting toroidal field of the magnetic base (i.e.: via the top flipping). In a vertical orientated spin axis configuration this gyroscopic property with its necessary precession allows it to respond dynamically to the field direction of the central magnetic gradient of the toroidally shaped field of its base magnet(s) and thereby remain self-centered in a restorative manner, levitating about an elevated central point within the base magnetic field where the forces acting on the top (gravitational, magnetic, and gyroscopic) are in a stable equilibrium thus allowing the top to stay hovering while resting in an energy minimum well.[8] (see: magnetic levitation)
In the laboratory, experimental setups are able to levitate tops for indefinite periods by measuring the spin rate and maintaining it using a drive coil. However, variations in temperature can affect the stability, and without ambient temperature control the top will eventually fall after hours or days due to the temperature coefficient of the magnets.[8]
The physics of the magnetic stability is similar to magnetic gradient traps.[8]
Inclined or horizontal spin axis levitation is accomplished by superposing a “macro-trap” on the precessional “micro-trap” first described by Sir Michael Berry[9] and Simon, Heflinger and Ridgway.[8] The macro-trap is generated by a combination of two magnetic “V”s as well as a puller magnet, situated directly above the Levitron. The puller acts like the string of a pendulum.
See also
References
- ^ U.S. patent 4,382,245
- ^ Theodore Gray (2 February 2004). "Ignorance = Maglev = Bliss". How2.0. Popular Science. Retrieved 2015-02-28.
This spinning top, which hovers above a magnetic base, was patented in 1983 by a Vermonter named Roy Harrigan.
- ^ "Magnets In Your Future".
- ^ Rod Driver (1999-09-22). "An amazing invention, and a patent failure (Part 1 of 2)". The Providence Journal. Alt URL
- ^ Rod Driver (1999-09-23). "The patent that failed its invention (Part 2 of 2)". The Providence Journal.Alt URL
- ^ Michaelis, Max M. (2012). "Inclined Levitron experiments". American Journal of Physics. 80 (11). American Association of Physics Teachers (AAPT): 949–954. Bibcode:2012AmJPh..80..949M. doi:10.1119/1.4742756. ISSN 0002-9505.
- ^ Michaelis, Max M (2013-12-18). "Horizontal axis Levitron—a physics demonstration". Physics Education. 49 (1). IOP Publishing: 67–74. doi:10.1088/0031-9120/49/1/67. ISSN 0031-9120. S2CID 121645252.
- ^ a b c d Simon, Martin D.; Heflinger, Lee O.; Ridgway, S. L. (1997). "Spin stabilized magnetic levitation". American Journal of Physics. 65 (4). American Association of Physics Teachers (AAPT): 286–292. Bibcode:1997AmJPh..65..286S. doi:10.1119/1.18488. ISSN 0002-9505. Retrieved 2006-12-06.
- ^ Berry, Michael Victor (1996-12-31). "The Levitron: an adiabatic trap for spins". Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences. 452 (1948). The Royal Society: 1207–1220. Bibcode:1996RSPSA.452.1207B. doi:10.1098/rspa.1996.0062. ISSN 1364-5021. S2CID 125190530.
This page was last edited on 26 April 2024, at 21:40