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 top acts as a gyroscope to prevent its toroidal magnetic field from aligning itself in the same direction as that of the primary field of the magnetic base (i.e.: 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 about 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. (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.
The physics of the magnetic stability is similar to magnetic gradient traps.
Read more about this topic: Spin-stabilized Magnetic Levitation
Famous quotes containing the word physics:
“It is hardly to be believed how spiritual reflections when mixed with a little physics can hold people’s attention and give them a livelier idea of God than do the often ill-applied examples of his wrath.”
—G.C. (Georg Christoph)
“But this invites the occult mind,
Cancels our physics with a sneer,
And spatters all we knew of denouement
Across the expedient and wicked stones.”
—Karl Shapiro (b. 1913)
“The fundamental laws of physics do not describe true facts about reality. Rendered as descriptions of facts, they are false; amended to be true, they lose their explanatory force.”
—Nancy Cartwright (b. 1945)