Tower Ride and Eddy Currents
Name: Denise A.
Date: Sunday, September 15, 2002
At Australia's Wonderland Theme Park there is a ride that
elevates a carriage of 4 seats up a tower 67 meters high. The carriage
'free falls' until the braking system comes into play. Apparently, 6
meters above the ground there are metal fins attached to the bottom of
the tower which "disrupt a magnetic field generated by pairs magnets on
each seat". (The pairs of magnets on each seat are positioned with
unlike poles facing and the tower fin comes between them). I cannot
understand how the disruption of the magnetic field fins effectively
causes a repulsion and hence the carriage to come to a stop. ( I am a
junior science teacher and a biologist not a physicist!)
This is a particularly beautiful application of Lenz's Law. A
changing magnetic field produces an electric field, either when the
field is moving relative to you or you are moving relative to the
field (Einstein thought about this most carefully, leading to his
Special Theory of Relativity).
If a conductor is moved through a changing magnetic field, the
resulting electric field will cause currents to be produced in the
conductor. Then, as for all currents in magnetic fields, there will
be a magnetic force on the conductor carrying the current.
Lenz's Law says that a force will be in a direction opposing the
change producing it. Since, in your example, the change is caused by
the magnets going downward, Lenz says the resulting force will be
upward, thereby stopping the carriage or at least slowing it.
Notice that if Lenz's Law were backwards, perpetual motion and free
energy would be present everywhere. Because if the force were in a
direction AIDING the change that produced it, the change would be
aided and increased, thereby producing an even larger force trying to
increase the change, and so on. The universe would instantly be blown
up! Luckily Lenz's Law is correct!
Richard J. Plano
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Update: June 2012