Magnet Questions

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Hello,

I'm a new member. If I am posting in the wrong forum please help by telling me where to post on this topic.

I'm interested in doing some science projects with my son. We've seen some interesting things with magnets. I want to be able to answer his questions about some of them.

Some of the questions are:

1. Can magnets be shielded so they do not attract nearby metals and/or other magnets? The way I described it was like helping Superman out by putting the kryptonite in a lead box so it can't harm him.

2. Do magnets weaken over time? If so how long does it take to happen?

3. If I take a magnet and force its north pole next to another magnet's north pole and keep them like that for a long time will they become weaker?

4. Is there a list of the metals that magnets will stick to?

5. If I had a metal container and filled it with magnet filings and sealed it with a metal lid would that container act as one large magnet?

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1. Yep you can, with lumps of metal which absorb all the field...

http://www.coolmagnetman.com/magshield.htm gives quite a nice explenation.

2. Yes, ferromagnets (what most people would just call magnets) are made up of lots of little magnets which all line up with each other, over time these become missaligned. The time this takes depends on the matterial and what is around the magnet. For example, take a piece of steel and rub it on a magnet it will hold some paperclips for a short while afterwards, now do the same with a piece of iron and it will hold the paperclips for much longer. For those wanting alot more info, hysterisys loops are the thing to research.

3. Yep this forces the small magnets I mention above to missalign with each other far faster.

4. Yes, at room temperature there is only really 3 pure metals, iron, cobalt and nickle, but there are lots more alloys like, steel and permally.

5. no, becuase the fillings inside the box would try and align to the least energetic state which would be when they are missaligned, if you put a field around them (magnet next to the box) this would make them move into a linged up position, if you then forced them to stick like this (poor in glue or something) this would work for a while.

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Another thing I want to add to this about magnets is that they are created by an electric current.

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This is great. Thanks for the info.

We are going to be working with neodynium magnets. Does the same thing apply to them as far as: 2. Do neodynium magnets weaken over time? 3. If I take a neodynium magnet and force its north pole next to another magnet's north pole and keep them like that for a long time will they become weaker?

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We are going to try the experiment that is shown on the following website called a Gauss Magnet Gun.

http://scitoys.com/scitoys/scitoys/magnets/gauss.html

My son says cool and I must admit I say cool too. So we have more questions. We don't have all our supplies yet or we would be able to answer these questions ourselves.

6. Can the ball bearings, that are positioned next to the magnets before the device is triggered, be attached to the ruler/track and not effect the device's action?

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1. Yep you can, with lumps of metal which absorb all the field...

http://www.coolmagnetman.com/magshield.htm gives quite a nice explenation.

Well ...

"The diagram in the middle shows what happens if you insert an iron plate between the magnets. No change? Actually, each magnet is now attracted to the iron plate, and don't see the other magnet on the other side of the plate!"

That's a bit of sematic games. The magnets still feel an attraction as the did before, but to something else. You have not shielded them from each other. And other than the superconductor, which actually excludes magnetic fields (up to a point, so it only works for small fields) you can't.

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IIRC, isnt Bismuth metal supposed to have some interesting effects with Magnets also?

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bismuth repels a magnetic feild. see if you can get hold of some pyrolytic graphite, the effect is more pronounced.

in the gauss gun, the ball bearings are in a higher energy state intitially than they are at the end. this position energy is released and sent down the track via a series of elastic collisions each adding energy to the next collision to send the last one off at high speed. it works much the same as newtons cradle it just has energy to release.

any ball bearing that is in contact with a magnet initially can be fixed in place but the device relies on the transfer of one ball bearing to the next magnet to both release and transfer kinetic energy.

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6. Can the ball bearings, that are positioned next to the magnets before the device is triggered, be attached to the ruler/track and not effect the device's action?

I just realized what I wrote doesn't read correctly. I meant: Can the individual ball bearings that are actually touching a magnet be attached to the ruler/track and not effect the device's action?

I realized the answer last night. They can be attached to the ruler/track. Here's why we think so. In normal operation the moving ball bearing hits the magnet (which is attached to the ruler/track) and transfers its energy to the magnet. The magnet is still able to transfer this energy to the ball bearing that is touching it. Therefore, if the magnet is attached to the ruler/track and still be able to transfer energy to the next ball bearing then that next ball bearing should be able to transfer that energy as well if it is attached to the ruler/track.

However, I think some of the energy that the magnet gains from the moving ball bearing is actually transfered to the ruler/track due to it being physically attached to it.

Does this sound right?

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IIRC, isnt Bismuth metal supposed to have some interesting effects with Magnets also?

It's a diamagnet (a very very strong one) which means in the presence of an external magnetic field it will become magnetised (and therefor magnets can stick to it). It can also quite eaily form an alloy which is a permanent magnet (ferromagnet).

I should have said above that diamagnetic materials will also stick to magnets.

There are quite a few of these and I know very very few

But ask me in a year when I'm further into my current research project and I should know some more

Enter_Narne, your son is very lucky to have an interested father that is prepared to do all this research for him.

(I wrote this several hours ago, but my net connection broke )

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Enter_Narne, your son is very lucky to have an interested father that is prepared to do all this research for him.

No. I am lucky to have a son. Period.

But thanks for the kind words.

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"4. Yes, at room temperature there is only really 3 pure metals, iron, cobalt and nickle"

Er, there's certainly a 4th; gadolinium is magnetic too. I did once hear that one of the crystal modifications of plutonium is too, but I don't feel like checking that one so I don't know if there's a 5th.

BTW, why do so many people spell nickel wrongly?

"I should have said above that diamagnetic materials will also stick to magnets."

No you shouldn't. Diamagnetic materials are repelled by magnets.

"It's a diamagnet (a very very strong one) which means in the presence of an external magnetic field it will become magnetised (and therefor magnets can stick to it)."

No, it doesn't mean that at all.

While bismuth and pyrolytic graphite are strongly diamagnetic as diamagnetics go, the effect is still weak compared to the effect of a magnet on a steel nail..

Most compounds are diamagnetic including water. Since yiou are mainly water you could be held up by a sufficiently stong magnetic field gradient.

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"4. Yes, at room temperature there is only really 3 pure metals, iron, cobalt and nickle"

Er, there's certainly a 4th; gadolinium is magnetic too. I did once hear that one of the crystal modifications of plutonium is too, but I don't feel like checking that one so I don't know if there's a 5th.

Gadolinium's Curie point is ~19 C, so whether it's ferromagnetic depends on how warm your room is.

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"4. Yes, at room temperature there is only really 3 pure metals, iron, cobalt and nickle"

Er, there's certainly a 4th; gadolinium is magnetic too. I did once hear that one of the crystal modifications of plutonium is too, but I don't feel like checking that one so I don't know if there's a 5th.

BTW, why do so many people spell nickel wrongly?

"I should have said above that diamagnetic materials will also stick to magnets."

No you shouldn't. Diamagnetic materials are repelled by magnets.

"It's a diamagnet (a very very strong one) which means in the presence of an external magnetic field it will become magnetised (and therefor magnets can stick to it)."

No, it doesn't mean that at all.

While bismuth and pyrolytic graphite are strongly diamagnetic as diamagnetics go, the effect is still weak compared to the effect of a magnet on a steel nail..

Most compounds are diamagnetic including water. Since yiou are mainly water you could be held up by a sufficiently stong magnetic field gradient.

Yes it was quite a while ago I read about diamagnetisim, their magnetic moments change making them exhibit a magnetism effect which will repell the field. My apologies. The lab I work in is kept at 21deg C by air con and is normally warmer due to all the kit so we don't treat gadolinium as a ferromagnet.

And as for the spelling *shrug* I'm dyslexic and missed the red squiggly line that firefox put in place. I suppose it's quite an easy mistake to make and not notice just as so many words finish le and el...

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Can magnets be shielded so they do not attract nearby metals and/or other magnets?

http://en.wikipedia.org/wiki/Mu-metal

Mu-metal is used to shield equipment from magnetic fields

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This is the same thing as I discussed in post 6, except you have a higher permeability than just iron (which also means you saturate at a lower external field). You can shield a region from magnetic fields, to some level, but two magnets will not be — they will now be attracted to the shielding material instead of each other, so there is still a force present.

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Since someone has dug up this thread I thought I'd mention that my sample of "99.9%" Gd is still magnetic (ie you can pick it up with a magnet) even when it's quite warm ie about 50C. It's a lot more strongly atracted to the magnet when it's cold.

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This is a bit off topic, and may be the substance of another thread, I'm not sure how involved the answer is.

My question is:

Can magnets ever be arranged so that the repelling force could be used to create perpetual motion? Like if there was a magnet attached to a center lever and magnets attached to the outer frame to push the magnet in the middle causing the lever to turn? I'm sure that people have attempted similar things, but I just wanted to know why it can't work. Thanks.

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there's a thing called back torque which seems to put a fail grade on any magnetism based perpetual motion device.

it you repel one magnet with another expecting it to pass another, you'll have a repulsion force acting. the closest that's possible is a magnetic bearing in a vacuum where almost all the kinetic energy stays put.

Ok thanks a lot

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