Spherical magnet dropped through aluminum pole rotates?

• Erwin Derek
In summary, Lenz's law states that dropping a magnet through an aluminum pole will cause an induced current that slows down its fall drastically. This can be observed by dropping a spherical magnet through an aluminum tube and noticing that it rotates to have its poles horizontal. This rotation is caused by the induced current creating a magnetic field that repels the magnet's poles, causing it to slow down. The resistivity of aluminum also plays a role in the strength of this effect.
Erwin Derek
Lenz's law shows that dropping a magnet through an aluminum pole will cause an induced current that slows down its fall drastically.

It has the following question:

Obtain such a spherical magnet that is slightly smaller than the inside diameter of the tube. The sphere will fall slowly down the tube just as the cylinder did. Mark the magnet "poles" with small colored stickers. Now watch the sphere from above as it falls down the tube. Does the sphere always rotate and re-orient so that one of the poles is up, and the other down? Or does it re-orient with the magnetic axis horizontal? Why?

I don't see any reason why the sphere would rotate. I think the net force exerted by all the induced currents should just point directly up regardless of what orientation the magnet is dropped. Can anyone explain if the sphere would rotate to have its poles vertical or horizontal, and why would it do this?

I am guessing it may have to do with the resistivity of aluminum or something...

The induced current in the aluminum creates a magnetic field that is opposite the direction of the field from the magnet. If the + pole is towards the direction of travel, the field that gets created just ahead of it will point towards the + pole and thereby repel it. A similar repulsion occurs if the - pole is towards the direction of travel. This should give a clue as to what you might expect to see.

The induced current in the aluminum creates a magnetic field that is opposite the direction of the field from the magnet. If the + pole is towards the direction of travel, the field that gets created just ahead of it will point towards the + pole and thereby repel it. This should give a clue as to what you might expect to see.

How about the field just before it? Wouldn't that field attract the upper pole just as much as the ahead field repels the lower pole?

If the field ahead of the magnet comes faster, maybe due to the resistivity of aluminum, then perhaps its repulsion would be a bit more than the attraction of the upper field? By this logic the ball might rotate so that its poles are horizontal... what do you think?

Erwin Derek said:
How about the field just before it? Wouldn't that field attract the upper pole just as much as the ahead field repels the lower pole?

If the field ahead of the magnet comes faster, maybe due to the resistivity of aluminum, then perhaps its repulsion would be a bit more than the attraction of the upper field? By this logic the ball might rotate so that its poles are horizontal... what do you think?
I think you are correct in that the upper pole experiences a pull on it to slow it down. Just a guess is that the slowing effect might get maximized for both poles when the magnet is horizontal, but it's just a guess.(Editing: I just read your second line=yes I think I agree with you, but I'm not 100% sure.) The region ahead will slow the pole and the region behind it will also pull on it to slow it, regardless of the polarity. ## \\ ## Additional editing: Also the magnetic field is strongest right at the surface near the axis of the poles, and this would have the most effect on the aluminum in the horizontal direction, inducing larger currents.

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1. What causes the spherical magnet to rotate when dropped through the aluminum pole?

The rotation of the spherical magnet is caused by the interaction between its magnetic field and the induced electric currents in the aluminum pole. This is known as the Lenz's law, which states that the direction of an induced current will oppose the change that caused it.

2. Can any type of magnet be used for this experiment?

Yes, any type of magnet can be used as long as it has a strong enough magnetic field to induce electric currents in the aluminum pole. However, the size and shape of the magnet may affect the speed and direction of rotation.

3. Does the thickness of the aluminum pole affect the rotation of the magnet?

Yes, the thickness of the aluminum pole can affect the strength of the induced electric currents and therefore, the speed and direction of rotation of the spherical magnet. Thicker poles may result in slower rotation.

4. Is the rotation of the magnet affected by the temperature of the environment?

Yes, the temperature of the environment can affect the rotation of the magnet. Higher temperatures can increase the resistance of the aluminum pole, reducing the strength of the induced currents and resulting in slower rotation.

5. How can this experiment be used in real-world applications?

This experiment demonstrates the principles of electromagnetic induction and its applications in technologies such as generators and electric motors. It can also be used to study the effects of magnetic fields on conducting materials, which is important in industries such as transportation and energy production.

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