Can I use magnets with opposite polarities to make a levitating sphere?
I’m trying to make a sphere that levitates inside a hemisphere cup lined with magnets glued down with all poles facing the same direction. The sphere is styrofoam lined with magnets with all the poles facing the same direction. So the hemisphere cup has magnets facing with the north pole out and the ball also has all of its north pole facing out. The cup covers about half the sphere, so the ball fits right inside. Is this possible to do?
I think Periphrasis has the right idea.
Some points to keep in mind:
You don’t want the magnets on the ball to touch each other. If they do, they will tend to act as one large magnet, with north on one side of the ball and south on the other.
You have to keep in mind that what will make the ball balance is equilibrium. In order to have a stable equilibrium, the geometry and the forces have to work in such a way that any displacement of the ball will create forces pushing it back toward the equilibrium position.
If the ball moves down, the repellent force needs to increase, so that it will move back up.
If it moves too high, the repellent force needs to decrease so that it will move back down.
If it gets off to one side, the force pushing it away from that side needs to increase (and the opposing force decrease), so that it moves back to the equilibrium position.
As Periphrasis points out, the upward force could pop it out of the cup. In particular, if it gets too high AND off to one side, it is doubtful that the lateral forces will be effective enough (once it rises above the sides) to move it back to the center.
Good luck!
yes
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Yes. It is good that you used styrofoam to minimise the weight and enhance the "levitation" aspect. The only problem I’m foreseeing is it somehow being too light and that magnets forcing it out over the edge of the cup…
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Not in practice because the sphere could not be placed exactly at the center of the cavity so there will be a force difference between sides of the sphere that will make it move, probably out of the cavity as was said by another. The only way I know to make levitation is with an aluminium body over a strong enough electromagnet feeded by alternating current (regular AC is OK). This principle is used by some electric fast trains (linear motor).
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I did this experiment while in College.
I think Periphrasis has the right idea.
Some points to keep in mind:
You don’t want the magnets on the ball to touch each other. If they do, they will tend to act as one large magnet, with north on one side of the ball and south on the other.
You have to keep in mind that what will make the ball balance is equilibrium. In order to have a stable equilibrium, the geometry and the forces have to work in such a way that any displacement of the ball will create forces pushing it back toward the equilibrium position.
If the ball moves down, the repellent force needs to increase, so that it will move back up.
If it moves too high, the repellent force needs to decrease so that it will move back down.
If it gets off to one side, the force pushing it away from that side needs to increase (and the opposing force decrease), so that it moves back to the equilibrium position.
As Periphrasis points out, the upward force could pop it out of the cup. In particular, if it gets too high AND off to one side, it is doubtful that the lateral forces will be effective enough (once it rises above the sides) to move it back to the center.
Good luck!
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Yes, attach the ball to a string from underneath, to keep the ball from getting pushed out over the top.
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I had a magnetic levitation project at the end of Uni. All the talking of physics is fine, but when you actually try to put it into practise, it’s hard to get any levitation stable.
You may find that magnets are too heavy, and that the repulsion isn’t strong enough to push it away. If you get magnets that are strong enough, then you may struggle to align them all with the north poles facing a certain way as they’ll flip over or snap together and hit your fingers. (Still have the scars!) No superglue will hold and they’re too brittle to screw!
If you’re after getting something to just levitate, use a diamagnet which will repel all magenetic fields. Pyrolytic graphite is a lightweight diamagnet to try. You could google "Levitator" think these are spinning discs which levitate…
Good Luck
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