Re: Magnetic Pendulums

From: On-line Snack discussion (snaktalk)
Date: Wed Jun 07 2000 - 18:38:03 PDT

I'm so sorry you had trouble with the Magnetic Pendulums Snack. I will
pass your e-mail on to the Snack experts. Did you see the other
postings about Magnetic Pendulums? Here are some excerpts from some of
them which you might find of interest:

from Wed April 21, 1999:
The length of the 2x4 boards doesn't really matter. The longer boards
will just elevate the whole apparatus a little higher off the table. The
only qualification to this is that if you use 18" 2x4's, you only have
2" to play with before the hanging coils start dragging on the table!
And it's not a good idea to shorten the length that the coils hang very
much, since it's easier to observe the swinging when the length is long.

The finer the wire, the more coils you can get in a compact space, and
the less the wire weighs for a given number of coils. But the finer the
wire, the higher the electrical resistance also. For 50 turns, the finer
wire might actually be better, since the resistance probably won't be
significant for that number of turns, and you'll have less mass to get
swinging. (50 turns is essentially a minimum. A few more probably won't
hurt!)

from Sun Mar 19, 2000:
You need to wrap two coils of wire for the magnetic pendulums snack
(each coil with at LEAST 50 turns -- more turns should enhance the
effect somewhat). Each coil should have a hole in the middle that is
about an inch in diameter. If the hole is too big, there will be too
much space between the coil and the magnet, and the magnetic field won't
be strong enough to do the job. If the hole is too small, the coil will
hit the magnet as it swings. Ideally what you want is the smallest hole
that will allow the coil to swing freely over the end of the magnet. So
you need to find something to wrap the wire around that is about an inch
in diameter -- a one inch wooden dowel, or a D cell battery would be
examples. A cardboard toilet paper tube is almost two inches, so it's
probably a little too big -- but you might overcome that by wrapping
more turns. When you're through wrapping, just remove the object that
you you used as the core, and you'll have the coil you need. You may
want to use some tape to keep the coil from coming apart.
You need to leave about three feet of wire unwrapped on each end of the
coil, so that you can position the coils on the wooden frame and connect
them, as shown in the drawing with the snack.
The lead with alligator clips is used only if you want to short the
coils out, as noted in the last paragraph in the To Do and Notice
section and explained in the last paragraph of the What's Going On
section.

from Tue Dec 29, 1998:
Here are some suggestions for the magnetic pendulums.
1. Be sure all electrical connections are good. If you are using enamel
coated wire, be sure that the enamel is scraped off the ends of the
wires where you join them. If there is plastic insulation on the wire,
be sure to strip it off. the ends where you join them.
2. Be sure that you are not using bare wires for the coils themselves,
or that the insulation has not been scraped off somewhere in the middle
of the coils. Enamel insulation is fine, but if somehow there is no
insulation at all on the coils, then you really just have a giant
one-turn coil instead of the 50 or more that you should have.
3. Be sure your magnets are cow magnets. These are stronger than many of
the old bar magnets sometimes found in schools.
4. Be sure that the coils are hanging so that they come to rest just at
the end of the cow magnets.
5. Be sure the coils are free to swing. If you're using #22 wire, you
might try a smaller diameter wire like #26. The finer wire is more
flexible, and allows the coils to swing more freely.
Beyond this I don't know what to tell you, without actually seeing your
construction. I've actually built one myself, and I've seen several
others built by others that worked, but this was all several years ago.

I hope something in the above helped.

Nina Thayer
Snacktalk Moderator
>
> My daughter and I have spent hours on the Magnetic Pendulums project. Not
> enough clear diagrams were posted. On the materials page it states that the
> 2x4 boards are to be 18 inches long. On the diagram it states 24 inches
> long. Which one is it? It also does not state how deep the cuts on the 1x4
> inch board is. Magnet wire is not covered so we cannot cut it. What kind of
> a lead wire with alligators clips and how long, there are several sizes.
> Also how far out of the front wood are the cow magnets supposed to go? We
> are very frustrated and disappointed on our project as we could not make it
> work.
>
> Roxy and Mari Shaw Vintage 53@aol.com or
> MLSMOUSE@aol.com
>

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