🚀 go-pugleaf

In article <1992Jul14.165115.29495@microunity.com>, wampler@microunity.com (Kurt Wampler) writes:

|>    Attractive levitation would require a much more complicated field shape.
|>    Just putting an electromagnet above the ball with sufficient field strength
|>    to begin to lift the ball will cause the ball to jump immediately to
|>    contact with the magnet.  The higher the ball gets, the stronger the field
|>    becomes.  To keep the ball floating away from the magnet above, it would
|>    probably be necessary to introduce a second magnetic field to cancel out
|>    the lifting field as the ball approaches the lifting magnet.  Good luck!


In fact, it is *impossible* to stably levitate a ferromagnetic
object by attractive magnetic forces from a static magnetic field.
The object always ends up being unstable in one direction.  It either
falls or runs up and sticks to the magnet.

Go look up "Earnshaw's Theorem" (sp?) in an EM text.

You can stably attractively levitate objects in an oscillating
field, even if the object being levitated has no induced currents
(as it would in a repulsive levitation scheme).  This doesn't require
feedback.  Just such a scheme was proposed for levitating a large
ring-shaped flywheel for utility load leveling:  the drag was
calculated to be so low that the ring would take a month to spin down
(in a vacuum).   The math turns out to be similar to that of
alternating gradient focusing magnets in particle accelerators.

	Paul F. Dietz
	dietz@cs.rochester.edu