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Levitating Magnets
Name: Anant J.
Status: student
Age: 18
Location: N/A
Country: N/A
Date: 3/7/2003
Question:
Why is it impossible to levitate a magnet over an
identical one when their like poles are facing each other? Why does the
upper magnet always flip over to be attracted by the lower magnet? If
gravity is pulling it downwards and the force of repulsion is acting
upwards, why can't it find an equilibrium position?
Replies:
It can find an equilibrium position, but the equilibrium is unstable--any
tiny flipping rotation results in an increased flipping force. It is like
a marble sitting at the very top of a dome.
Tim Mooney
It is possible in principle. The problem is that if the magnet is displaced
even ever so slightly from the equilibrium position, the force pulling it
over increases. It is a little like trying to stand a stick up straight on
a perfectly slippery surface with a very fine point on the bottom of the
stick. It's possible in principle, but you just cannot do it.
It might work if you use another magnet above the top one to keep it
balanced. It might work if it is close enough to keep the magnet from
falling over but far enough not to lift it up. It is a little like tying a
weak rubber band to the top of the stick.
Best, Dick Plano, Professor of Physics emeritus, Rutgers University
Anant,
Have you ever looked at the pictures of magnetic field lines around a
magnet as depicted in books. They are very "round". What you are trying
to do is to balance one ball on top of another. This is an unstable
situation. Gravity will always be pulling the top magnet down and it will
slide down the slope of the magnetic field lines of the lower
magnet. Once it gets far enough down, the opposite poles will start to
interact and the top magnet flips over.
Greg Bradburn
The equilibrium position it can find is known as an "unstable"
equilibrium: any displacement from the equilibrium position will cause the
system to move farther away from, rather than back toward, the equilibrium
position. Since there is no margin for error, you cannot keep it there.
Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois
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Update: June 2012
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