Physics Q (x post)

[m_the0ry]

This doesn't have anything to do with magnetostatics as far as I can tell. This is an effect of gravity. The spinning magnets tilt towards earths gravity (down) and put more friction between the surface there, meaning more force on the bottom half of each part of the rotation at the glass/magnet interface, causing it to move right when spun clockwise and left when spun counterclockwise. Just like a wheel.

[jkkkk]

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This doesn't have anything to do with magnetostatics as far as I can tell. This is an effect of gravity. The spinning magnets tilt towards earths gravity (down) and put more friction between the surface there, meaning more force on the bottom half of each part of the rotation at the glass/magnet interface, causing it to move right when spun clockwise and left when spun counterclockwise. Just like a wheel.

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I was starting to think my solution was way too simple to be correct, but I believe this is the correct answer.

As the magnet starts to fall towards the earth due to decreased friction, there begins an inbalance in the friction between the lower and upper contact points of the spinning metal upon the glass. The lower part of the glass becomes an area of increased friction due to both the shape of the magnet and the fact that the friction created by the magnet moving downwards affects the bottom part of the spinning metal most. Thus when the magnet is spinning clockwise, the metal at the bottom spinning to the left in a U shape manner pushes the magnets right, just like a wheel would.

This is correct, no?

[gumpzilla]

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This doesn't have anything to do with magnetostatics as far as I can tell. This is an effect of gravity. The spinning magnets tilt towards earths gravity (down) and put more friction between the surface there, meaning more force on the bottom half of each part of the rotation at the glass/magnet interface, causing it to move right when spun clockwise and left when spun counterclockwise. Just like a wheel.

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I was starting to think my solution was way too simple to be correct, but I believe this is the correct answer.

As the magnet starts to fall towards the earth due to decreased friction, there begins an inbalance in the friction between the lower and upper contact points of the spinning metal upon the glass. The lower part of the glass becomes an area of increased friction due to both the shape of the magnet and the fact that the friction created by the magnet moving downwards affects the bottom part of the spinning metal most.

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This last bit is why I was going on about velocity-dependent friction in the other thread. I'm not sure what the argument for increased friction on the lower side is if you don't have such a thing. However, the argument that the shape isn't flat and will lead to tilting downward would mean greater pressure there and thus more friction seems solid. And you're right that if there were more friction on the bottom side, then it would have this effect.

I'm with the people that say that the magnetism is probably a red herring here. I think the only reason it is necessary is to give you something that will keep the frictional force for you. A pretty quick experiment that should address these concerns: take a pane of glass, and lay it parallel to the floor. Set up your magnets on that system and spin them. Without the gravitational asymmetry, by these arguments they shouldn't have the same left-right behavior. (I think the actual dynamics will be complicated because of coupling between different axes of rotation from the weird shape. That is, spinning it will lead to pitching and rolling on the other axes.)

EDIT: For that matter, spinning one of these things by itself on a flat surface should do the trick for debunking the magnetic claims, I think. I think the key thing here is that if it were the magnetic fields, the force wouldn't always be to the right, as the whole thing should be rotationally invariant, and would always be to wherever the "right" is right now.

[gumpzilla]

An addendum to my last post: the rotational invariance will be broken by the Earth's field, but if these are neodymium magnets as I think their field is going to be one hell of a lot stronger. And again, if it were the Earth's field breaking the symmetry then spinning one of these bad boys by itself on a flat surface should exhibit the same behavior.

[jkkkk]

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For that matter, spinning one of these things by itself on a flat surface should do the trick for debunking the magnetic claims, I think. I think the key thing here is that if it were the magnetic fields, the force wouldn't always be to the right, as the whole thing should be rotationally invariant, and would always be to wherever the "right" is right now.



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Exactly.

[Magic_Man]

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This doesn't have anything to do with magnetostatics as far as I can tell. This is an effect of gravity. The spinning magnets tilt towards earths gravity (down) and put more friction between the surface there, meaning more force on the bottom half of each part of the rotation at the glass/magnet interface, causing it to move right when spun clockwise and left when spun counterclockwise. Just like a wheel.

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I was starting to think my solution was way too simple to be correct, but I believe this is the correct answer.

As the magnet starts to fall towards the earth due to decreased friction, there begins an inbalance in the friction between the lower and upper contact points of the spinning metal upon the glass. The lower part of the glass becomes an area of increased friction due to both the shape of the magnet and the fact that the friction created by the magnet moving downwards affects the bottom part of the spinning metal most. Thus when the magnet is spinning clockwise, the metal at the bottom spinning to the left in a U shape manner pushes the magnets right, just like a wheel would.

This is correct, no?

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Easy enough to test. OP, can you spin them on a horizontal plane and let us know if they still move in predictable directions?

[PairTheBoard]

Sans the horizontal test, I think a good thing to look at is How Much the magnets curve to one side or the other. I can't imagine friction causing that big a curve for relativley dense magnets. If it's a pronounced curving I'd be more inclined to suspect the magnetowatchamacallit effect. Possibly from some kind of lag in the polarity of one magnet catching up to the polarity of the other.

PairTheBoard

[gumpzilla]

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Sans the horizontal test, I think a good thing to look at is How Much the magnets curve to one side or the other. I can't imagine friction causing that big a curve for relativley dense magnets. If it's a pronounced curving I'd be more inclined to suspect the magnetowatchamacallit effect. Possibly from some kind of lag in the polarity of one magnet catching up to the polarity of the other.

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The speed of light isn't fast enough these days? From the description they're spinning basically in tandem anyhow. And I'm still unclear on what would break the rotational symmetry of the problem. So basically I think friction is a much more compelling answer.

[PairTheBoard]

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Sans the horizontal test, I think a good thing to look at is How Much the magnets curve to one side or the other. I can't imagine friction causing that big a curve for relativley dense magnets. If it's a pronounced curving I'd be more inclined to suspect the magnetowatchamacallit effect. Possibly from some kind of lag in the polarity of one magnet catching up to the polarity of the other.

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The speed of light isn't fast enough these days? From the description they're spinning basically in tandem anyhow. And I'm still unclear on what would break the rotational symmetry of the problem. So basically I think friction is a much more compelling answer.

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Would you still think that if they curve to the right the same distance as they fall downward? We haven't been told how much they curve yet.

As far as spinning in tandem, I doubt they are so strongly bonded by the magnetic force that they start off spinning as if they were attached to each other. There is bound to be a slight lag at least in the beginning as the magnet on the other side of the glass tries to realign its polarity with the one with force being applied to it. Another test that could be done is to apply equal spinning force to both magnets simulateously and see if they still curve to the right the same way they do when the force is applied to just one magnet. Yes, the magnetic field propagates at the speed of light. That doesn't mean it's force on the non-pushed magnet is equivalent to the physical force being applied to the pushed magnet, or that the nonpushed magnet catches up to the sudden increase in rotational speed of the pushed magnet at a speed of light rate of catch-up. In fact, the non-pushed magnet may never completely catch up it's polarity alignment with the pushed magnet. Yet another thing to measure is whether the rate of magnet curvature is constant. If it's due to friction it should increase to a maximum rate as the magnets fall. If it's due to magnetic imbalance from polarity lag it should decrease as the lag decreases.

PairTheBoard

[PairTheBoard]

I just reread the OP and notice he describes the magnets as "shifting" to the right. That doesn't sound like they fall and slowly curve to the right. It sounds like they make a sudden "shift" to the right and then fall downward. If this is correct, it sounds much more likely to be caused by the lag in the back magnet's position of polarity catching up to the front magnet's rotated position of polarity. The effect is most pronounced right at the beginning. Once the polarities get back in opposite synch the effect goes away and the magnets, after shifting to the right drop down more and more straight as their rightward momentum is slowed by friction.

Someone else will have to explain how out of synch polarities act to force the shift to the right.

PairTheBoard