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Question:
I have a question involving magnets and force. I could not find the answer anywhere and do not quite know if I can use logic to answer. I have two neodymium magnets and each magnet has the ability to pick up and object 10 pounds. So if you used both together it could pick up an object 20 pounds. Now if I placed one of them on a table and then forced the other on top so they would repel and released it, the one on top would shoot off. My question is that when I release it will it fly off as a result of 20 pounds pushing it up?



Replies:
You have a number of intertwined things going on in your "thought" experiment. I am not knocking "thought experiments" even Einstein himself used them magnificently in his many contributions to physics. I am sure I do not cover them all, but here are some of the "conditions" and possibilities.

Assume the two magnets are ellipsoids of revolution, magnetized along the "long" axes, constrained in a cylindrical tube with N/N or S/S poles. The repulsive force between the two magnets will be complicated, but can be solved "in principle". The separation between the two magnets will be a balance of the repulsion of the N/N or S/S repulsive poles and the force of gravity. In the absence of any gravity the two magnets would fly apart indefinitely (more or less). In the presence of gravity, acting exclusively along the axis of symmetry between the two magnets, the two magnets will come to rest when the repulsion between them is balanced by the force of gravity. This is a much simpler configuration than you suggested of having the two magnets flat on a table -- in which case the two magnets will spin around until they align N/S and S/N. Thinking "out loud", if you could measure the distance between the repulsive N/N or S/S poles accurately, I am thinking of interference fringes of a laser pointer for example, it might be possible to relate that distance to the local force of gravity, which of course changes from place to place on the surface of the Earth. Or a similar arrangement might be used to measure the local magnetic field of the Earth. Your question raises a lot of interesting issues.

Vince Calder



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