Re: Magnetic pendulum (fwd)

From: Paul Doherty (
Date: Wed Oct 01 2003 - 18:31:22 PDT


The reason we removed this from our snack list was not because the force
was too small, but rather that people could not reliably make a pivot for
their pendulums which would swing cleanly and easily and yet not collide
with the magnet.

We're waiting for inspiration aboout how to design a simple easy too build
precise frictionless (or low friction at least) pivot for our pendulums.

Neodymium magnets do work better than cow magnets by about an order of
magnitude x10.

Paul Doherty

>---------- Forwarded message ----------
>Date: Wed, 17 Sep 2003 16:29:37 EDT
>Subject: Magnetic pendulum
>I noticed that this snack was removed from your list of snacks. Was that
>because it does not work very well?
>I was reading a feedback from a father who was trying this project with his
>child. He complained that the effect was not great enough and attributed it
>to the type of wire he used. He had the very slightest effect using
>wire and not magnet wire. So how can the effect be increased? The
>magnetic induction causing the force apparently is not very strong. To
>move an
>object most readily, the mass to be moved must be very small. That would
>the coiled wire and the rod supporting the wire. For maximum effect you
>want more turns of wire. However, that increases the mass. So the lighter
>wire (smaller gauge) makes sense but so would a lighter support rod. The
>induced EMF in the wire also depends on the strength of the magnetic
>field. So,
>use a stronger magnet. A cow magnet is strong but not as strong as a
>neodymium magnet. They don't make cylindrical neodymium magnets as far as
>I know so
>you can't just drill a hole for the cow magnet but must find some way of
>mounting the rectangular neodymium magnet. Perhaps drill a series of
>holes and then
>use a chisel to knock out the rest of the wood forming a rectangular hole.
>The force should also depend on the rate at which the area is changing so the
>faster it swings, the better? So start the swing at least twice as high as
>the position of the secondary coil???
>I have never done this experiment but it sounds really neat. I did not see a
>response to the father who wrote the orginal email in 1998.
>R. Clements

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