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Whoever knows a magnet has two magnetic poles, named North and South, that same poles repel each other (N-N or S-S), and opposite poles (N-S) attract.
This behavior allows the construction of this classic "Magic Rocker":
Let's see how this simple model is built:
Letters N and S identify the poles of each rod end: spheres 1 and 2 are attached to two north poles each, so they have a strong north magnetization and will repel each other when the model is folded. Spheres 3 and 4 are neutral, since they are attached to a north and a south rod end. Spheres 5 and 6 are strong south: so the south-pole magnetized sphere 5 attracts to the neutral sphere 3, and the same occurs between spheres 6 and 4.
But how can we discover which geomag rod end is a North, and which is a South? Actually, this is not a real problem, since if all the rods in the model above were inverted (so, for instance, spheres 1 and 2 were South) the model worked exactly the same.
So we can work in a different way. Let's take a geomag rod, and identify one of its ends with some adhesive tape:
For our needs, it's indifferent if the taped end is a North or a South: we need only to concern about Attractions or Repulsions with respect to this taped end. Let's modify the image of the rocker model:
In the image above the letter R identifies the rod ends that need to repel the taped end of our "standard rod" (of course, if one rod end repels it, the other end will attract: hence no need to identify the two polarities of each rod).
This way to check for rod polarities becomes really useful when the model to build is more complex. When I started watching Geomag models on youtube (on 2007), I found something similar to this model:
The base is made out of two pentagons and two squares (the model has a total of 34 rods and 16 spheres). It seems to be a really easy easy model to build, but there are many magnetic poles to check:
There are 8 rods that need to be corectly placed to get the correct magnetic fields; in addition, a special care is needed with respect to the central spheres of the base, those where the yellow triangle will be attached (I don't explain all in detail: try it yourself!). Well, I can guarantee to build this (not too complicated) model the "taped rod" is a most useful tool!
When I saw this double-repulsion-pendulum on youtube I immediatly wondered how to get a more interesting model. I obtained an "inverted pendulum", built with some 500 Geomag rods (I mean the PRO rods, shorter than those shown in this article). if you are interested in this model, you can watch it clicking here (sorry for the poor quality!), but I'll now show you how to build a really simple, working model, with the KIDS size rods.
Let's start with a simple pentagon with 5 rods starting from its vertices and joining on a central sphere: all of these 5 rods will be placed as to repel the "taped rod" on the central sphere:
On the base pentagon we build a prism like this:
and continue adding prisms (the front square panel is not mounted to help see what will happen inside the model):
Now we add a truncated pentagonal pyramid
and a decagonal prism:
The model skeleton is now built. We now need to add the repulsive poles:
20 Geomag rods are attached to the vertices of the upper prism, and each rod must have the repuslive end (of course, repulsive with respect to our taped rod) directed towards the center of the model.
Now it's the time to add the pendulum:
The pendulum is made of 5 rods, with the repulsive end placed upwards. The model has a total of 115 rods, and works something like this:
Again, if you are interested in watching the complete youtube clip of this model, click here.
Article written by Guest Blogger Aldo Cavini (aka aldoaldoz)
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