Levitron

From Wikipedia, the free encyclopedia

A Levitron is a device consisting of a magnetic spinning top that floats mid-air above a base unit by means of spin stabilized magnetic levitation . The name Levitron is trademarked by Creative Gifts, Inc.

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

[edit] Operation

Making the Levitron levitate is not trivial, and the procedure 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 will never rise above the plate, and if the top is too light, it will fly off in a random direction. For this reason, washers of various masses are 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 ferromagnetic materials against gravity. This theorem does not apply to the Levitron, however, because the non-static nature of the spinning top acts as a gyroscope to prevent the magnetic field of the top (a magnet) 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 force minima at a central point in space above the base. ^[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.