Levitron

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Levitron is a registered trademark of Creative Gifts, Inc., used to advertise a range of toys and gifts in the science and educational markets. The Levitron top device is a commercial toy that displays the phenomenon known as spin-stabilized magnetic levitation. Consisting essentially of a permanent magnetic top and base plate, ring or alternate geometric configuration, the toy's construction is relatively simple. The theory behind the Levitron, however, is considerable and remains incomplete, while functional parameters, such as the top rotation rate or top weighting, are considered somewhat stringent. Employing principles of the magnetic field and gyroscopic stabilization, the Levitron induces levitation in its top through a series of interactive steps as described under Operation. The levitated top's stabilizing rotation undergoes natural, gradual diminishment; consequently, unless spin-sustaining measures are employed, the levitation interval generally does not exceed four minutes.

1 Operation
2 Physics
3 Trademark Litigation history
4 References
5 External links

[edit] Operation

Levitating the Levitron is not trivial and can be difficult to learn. First, a plastic plate is placed on top of the magnetic base, and the top is spun on the plate. Then the plate is lifted by hand until, if all the conditions are right, the top rises above it to the equilibrium point. If the top is too heavy, it cannot rise above the plate; too light, and it flies off. Washers of various masses are thus included in the kit that can be placed on the spindle of the top to adjust its weight. The spin rate of the top must also fall within a narrow range around 25 rotations per second. Since it can be difficult to spin the top fast enough by hand, Creative Gifts makes a battery-powered, handheld device to spin the top with an electric motor. After a few minutes, the top falls when air friction slows it below the critical speed.

[edit] 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 the Levitron magnetic top device, however, due to spin stabilized magnetic levitation whereby the top acts as a gyroscope to prevent the magnetic field of the top from aligning itself in the same direction as that of the magnetic base (ie: via the top flipping). This gyroscopic property combined with the top's precession allows it to respond dynamically to the direction of the local toroidally shaped field of its base magnet and remain levitating in a central point in space above the base where the forces acting on the top (gravitational, magnetic, and gyroscopic) are in equilibrium thereby allowing the top to rest in an energy minima well. ^[1] (see: magnetic levitation)

[edit] Trademark Litigation history

Levitron was the source of trademark litigation in United States District Court of New Mexico. Creative Gifts, Inc., the owner of the Levitron trademark, brought suit against Michael and Karen Sherlock and their company UFO, alleging infringement and seeking a permanent injunction. The district court, Judge LeRoy C. Hansen, held that the mark was infringed, and rejected all of the Sherlocks' defenses and counterclaims.

On appeal to the Tenth Circuit Court of Appeals, the Levitron mark was enforced in favor of its owner. Creative Gifts, Inc. v. UFO, 235 F.3d 540 (10th Cir. 2000)(New Mexico). Specifically, the court affirmed the district court (1) that the term 'Levitron' is not a generic term, and that the specific categories of evidence proffered by the Sherlocks in support of their claim, including internet sites purporting to demonstrate generic use, failed; (2) that the district court's assignment of the levitron.com domain originally procured by the Sherlocks to Creative was proper; (3) that no theory of promissory estoppel could be asserted against Creative by the Sherlocks; and (4) that no "naked license" of the Levitron mark had been granted by Creative. All 23 of the counterclaims made by the Sherlocks were rejected. The court affirmed a permanent injunction against the Sherlocks.

[edit] References

^ Martin D. Simon, UCLA Department of Physics, Lee O. Heflinger, S. L. Ridgway (1997). Spin stabilized magnetic levitation (HTML). American Journal of Physics. Retrieved on 2006-12-06.