We have a very similar demo that is in our lecture hall. That one uses
various plates (conductive, non-conductive, slotted, ferrous, non-ferrous)
that swing between the poles of a single, very large (and very old,
probably 1960s), horseshoe magnet. I'd guess that the poles are about 4 cm
apart.
The plates are round disks that swing like a pendulum. They are about 15 cm
in diameter. Each has two holes near the edge and about 7 or 8 cm apart.
Those go up to a ring stand clamp with a horizontal bar. Strings of all
equal length run from the two holes to two places on the bar. A bit hard to
describe. Each hole has two strings one to one position on the bar and one
to another with the two spots separated by about 7 or 8 cm. What this does
is allows the disks to swing with minimal rotation. So they swing very
uniformly. I do not have a photo, sorry.
It is something like this but with disks and strings rather than a
gondola/boat: https://www.shutterstock.com/search/swinging-boat-amusement-park?image_type=photo&page=2
Swinging without the magnet in place is very smooth and does just what
you'd expect. Goes back and forth.
The nice thing about the steel plate is that it violently slams into the
magnet and stops with a clang. Now all the other plates show that it is NOT
magnetic attraction that is at play here. And, it has now riveted every
student's attention.
The plastic plates just swing.
The aluminum and copper plates come to an immediate halt without slamming
into the poles.
The aluminum and copper plates with lots of slots cut into them are barely
affected by the magnetic fields since it is hard for eddy currents to form.
This setup is great (and one of my favorites) for a lecture demo. Probably
not so good for a public hands-on display. I'll bet it could be modified
though with stronger supports and some thinking where it could work in that
setting. Maybe replace the strings with rigid wood dowels or carbon fiber
rods going up to two bearings on the horizontal support. That would swing
uniformly everytime.
John
- - - -
John E. Sohl, Ph.D.
WSU Brady Presidential Distinguished Professor Emeritus
Department of Physics and Astronomy
Department of Environmental Science
Department of Being Retired and Loving It
Weber State University
cell: (801) 476-0589 (Text me, I don't answer the phone if you are not in
my contacts.)