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# Magnetic spec Answered

I was wondering how big a cylinderical grade N42 NIB magnet i would need to pull a copper weight of 20 grams from 3inches? I dont know how to calculate so... If you could, that'd be great

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I don't know if this will be any help, but when they say "56 lbs force" they mean it. I bought two of the 56 lb 1"x1"x3" and received them today. After finally prying them apart, they slammed back together crushing my ring finger. The nail's already solid black. On impact they threw sparks and shattered. (I'm out \$30 pretty quickly.) I've now decided that magnets are scary, and I'm going to go back to playing with a glue gun and balsa wood.

Late breaking news:
KJ Magnetics has been putting together graphs of "pull force vs distance" for the magnets they sell... I won't be terribly useful; they measure force in pounds, so a 1/2*1 inch magnet goes from 16 lbs at 0 to "essentially 0" at 1.2 inches, even though we know from experience that small forces extend well beyond that distance.
Now all you have to do is figure out what "pull a weight" means: just overcome sliding/rolling friction, lift it straight up (20g of force), something else?

I don't know how to calculate
Neither do I, and I have an A-level and a bit of a degree in Physics. My suggestion is buy one of those big tubs of magnets from ThinkGeek and experiment.

"Static" magnetic is way harder to do simple calculations like this with than electricity.

Copper isn't magnetic..

Your name fits you well...

Sorry guys. Its actually a copper plated steel im thinking of. Only said copper because thats how it appears, it a steel weight of around 20 grams. Any help now?

If it has a copper coating, it still won't be magnetic. The steel has to be touching the magnet...

afraid thats not terribly correct, i know for a fact that this copper plated steel eight can be moved using a magnet, i am merely asking how big a magnet would you need to pull a 20gram steel weight form 3 inches? If you don't know, just say so

The best answer I can give is "not very", especially if you're rolling the cylinder across a smooth horizontal surface. A 10mm counter-sunk magnet will pull a medium-sized nail from three inches on the horizontal.

The first semi-logical answer to this post, cheers. How much are we saying a medium sized nail might weigh?

Hmm... I'm not allowed to weigh them on the kitchen scales, and the bathroom scales won't register the jar... Guessing - 10-20g? Can I ask what you're actually trying to do?

Im afraid im sworn to secrecy on that one, but you have been very helpful none the less. Thanks

>slap< You know better than that! Magnetism is a non-contact force - one of the three genuine force-fields (the other two being electro-static and gravity) - and can reach right through non-magnetic materials. That's how reed switches work.

>slaps self<