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Hi! Recently I saw a wikipedia article that gave information on an interesting device called a SMOT (simple magnetic overunity toy). Of course, the toy does not violate the laws of thermodynamics but I thought it was really cool how one can make a metalic sphere go from "point A" to "point B" by slightly tilting two magnets toward each other. I was wondering, how would it be possible to calculate the momentum of a metal ball that passes thru a SMOT device? For the metal ball to accelerate past the point at which the magnetic fields are the strongest, would the momentum of the metal ball need to be stronger than the strength of the magnetic force? How would I be able to calculate the magnetic force on the ball, to compare it to the momentum of the ball?
Answer 1:

The magnetic force on the ball changes as the ball moves through the magnetic field. In order to calculate what the total work done on the ball is (and thus its kinetic energy and from that its momentum), you will need to use calculus.

Fortunately, as a college student now, calculus is probably the first college-level math class you will take, if you haven't already at the end of high school. If you haven't been exposed to calculus yet and are anxious to get started right now, I suggest you check out the Wikipedia article on "derivative" and work through the examples. There are ALL KINDS of cool things you can do with derivatives (e.g. ever wondered WHY the one-half part of the distance-acceleration formula is there? Velocity is the derivative of acceleration, and position is the derivative of velocity...). If you HAVE been exposed to calculus already, then the thing you need to do to get the work done on the metal ball is to integrate the force over the distance traveled. Once you have the kinetic energy, you can get the velocity, and from that, the momentum (assuming of course you know the mass of the ball, which you also need).

Have fun!


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