# Magnets - science question.

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Here is a question for a science person.

I am working on a cool cache contraption, I am looking to use a magnet with a rated 30 lbs pull force.

My question is, if 2 of those magnets are "stuck" to each other is there a 60 lbs force required to pull them apart? If not, what would be the force required to pull them apart?

Any help would be greatly appreciated.

Thank you,

--Dutch

I think the force would be doubled but I'm not sure.

My significantly more intelligent other half has pointed out that anyone with a pacemaker is going to want to give that cache a wide berth wouldn't want it switching off suddenly!

I think the force would be doubled but I'm not sure.

My significantly more intelligent other half has pointed out that anyone with a pacemaker is going to want to give that cache a wide berth wouldn't want it switching off suddenly!

Yeah I will put a warning on the cache page and near the contraption itself, untouched the contraption will be 16'-20' feet up on the air so it will be far away from any pacemaker.

Back to the original

Does somebody know about the pull force for sure?

EDIT: Maybe I should add that they are 1/2" cube magnets.

Edited by linuxxpert

Holy smokes!

Be careful with those!

I know the little 1/4"x1/8" inch rare earth button magnets have actually given me a blood blister when they snapped together on me.

In answer to you question, from Wikipedia:

Force between two magnetic poles

The force between two magnetic poles is given by:

F is force (SI unit: newton)

qm1 and qm2 are the pole strengths (SI unit: ampere-meter)

μ is the permeability of the intervening medium (SI unit: tesla meter per ampere, henry per meter or newton per ampere squared)

r is the separation (SI unit: meter).

Basically, you don't add the force of the poles, you multiply them.

One of those cases where 2+2 doesn't equal 4.

Oh... wait... 2X2 does equal 4. Well 3+3, then...

Woah, where do you get hide-a-car magnets?

Edited by Airmapper

Maybe this stuff really IS rocket science after all:

http://www.rare-earth-magnets.com/pull_force_calculators.htm

That calculates magnet to steel... I have that; 30 lbs.... just cant figure out what magnet to magnet would be at least with the limited information I have.. I already ordered the magnets so maybe I should just wait and experiment. Maybe someone can give me a ballpark number?

Hopefully the epoxy will hold, I want to use JB weld to glue the magnets to aluminum.. think this will work? Should I rough up the magnets and aluminum first? Its gotta be strong!

Maybe this stuff really IS rocket science after all:

http://www.rare-earth-magnets.com/pull_force_calculators.htm

That calculates magnet to steel... I have that; 30 lbs.... just cant figure out what magnet to magnet would be at least with the limited information I have.. I already ordered the magnets so maybe I should just wait and experiment. Maybe someone can give me a ballpark number?

Hopefully the epoxy will hold, I want to use JB weld to glue the magnets to aluminum.. think this will work? Should I rough up the magnets and aluminum first? Its gotta be strong!

Ok, ok, I promise to never apply for employment at NASA.

Maybe this one will calculate it for you?

I won't wear a Belt Buckle when I come find the cache and I'll leave my credit cards in the car so they won't get erased...

When you add a proton and a neutron the weight of what you get is less than the sum of the weights of the parts, by only the tiniest percentage but that's what makes an H bomb work the way it does.

In your case, yes twice the force. As long as you are pulling exactly perpendicular to the faces of the magnets. If you can slide the magnets sideways then it's a heck of a lot easier, so contraption your device in such a way that you can't slide and you will be guaranteed to make it hard for cachers, or muggles, to pull it off.

Sorry for all the puns in all these sentences.

Edited by trainlove

With such strong magnets should one worry about having their electronics (GPS and PDA in the case of cacher) near this thing?

A Strong Magnetic Cache was hidden at this stadium...and it pulled a Meteor right out of the sky.

A Strong Magnetic Cache was hidden at this stadium...and it pulled a Meteor right out of the sky.

I am glad I did not get the 60lbs ones!

When you add a proton and a neutron the weight of what you get is less than the sum of the weights of the parts, by only the tiniest percentage but that's what makes an H bomb work the way it does.

In your case, yes twice the force. As long as you are pulling exactly perpendicular to the faces of the magnets. If you can slide the magnets sideways then it's a heck of a lot easier, so contraption your device in such a way that you can't slide and you will be guaranteed to make it hard for cachers, or muggles, to pull it off.

Sorry for all the puns in all these sentences.

Thank you trainlove, thats exactly the answer I was hoping for... this is going to be great!

Remember... 60 pounds of force is probably also sufficient to break bones if your hands or fingers were to get in the way.

Remember... 60 pounds of force is probably also sufficient to break bones if your hands or fingers were to get in the way.

Not a problem, one end will always be 16'-20' up in the air..... just hoping that cachers will be strong enough to pull these 2 magnets apart!

Unless you meant that "I" should be careful handling them... then I thank you for your concern

Maybe this stuff really IS rocket science after all:

http://www.rare-earth-magnets.com/pull_force_calculators.htm

That calculates magnet to steel... I have that; 30 lbs.... just cant figure out what magnet to magnet would be at least with the limited information I have.. I already ordered the magnets so maybe I should just wait and experiment. Maybe someone can give me a ballpark number?

Hopefully the epoxy will hold, I want to use JB weld to glue the magnets to aluminum.. think this will work? Should I rough up the magnets and aluminum first? Its gotta be strong!

Jb Weld has Iron powder mixed in it. When you use it with a magnet the iron will migrate along the magnetic forces exerted by the magnet.

My experience showed that the JB Weld used a lock-n-lock with a magnet the epoxy crawled up the side of the 1" dia. by .125 thick magnet and ended up with at least half of it on top of the magnet.

I would use an epoxy without metal in its mix. Roughing up the surface will help the epoxy's ability to adhere to metal surfaces.

Nevermind...I must have missed a very important post...disregard

Edited by cowcreekgeeks

One issue here is that as the rare earth magnets are allowed to snap together with a great force they may fracture and splinter or crumble.

With lesser powered magnets the mere act of one hitting another in the force they exert as they 'snap' together can sometimes cause them to be in pieces.

It is worth noting in your application that not all that may put them back together may be fully aware of this fact.

Edited by artist2c

One issue here is that as the rare earth magnets are allowed to snap together with a great force they may fracture and splinter or crumble.

With lesser powered magnets the mere act of one hitting another in the force they exert as they 'snap' together can sometimes cause them to be in pieces.

It is worth noting in your application that not all that may put them back together may be fully aware of this fact.

Maybe a bit of adhesive felt between the magnets would dampen the blow?

One issue here is that as the rare earth magnets are allowed to snap together with a great force they may fracture and splinter or crumble.

With lesser powered magnets the mere act of one hitting another in the force they exert as they 'snap' together can sometimes cause them to be in pieces.

It is worth noting in your application that not all that may put them back together may be fully aware of this fact.

Maybe a bit of adhesive felt between the magnets would dampen the blow?

I've done a fair amount of work with rare-earth magnets (not "earth" magnets, as some call them). You can get rubber coated ones from some sources, but the rubber coating does lessen the attraction to some extent.

Yes, they are brittle and can "explode" if allowed to slam together. They can also pinch and cause blood blisters and even broken bones. And don't forget that if they pinch you, you've got to pull them apart to get that skin out. I recently bought some with 52 lbs attraction, and its all but impossible to separate them without a specialized tool.

Don't try to roughen them up. First of all, if they are chrome plated (most are) you won't have any luck. Second, if you do, you'll be removing the anti-oxidation coating, and these things corrode very quickly without it (paint or the epoxy would of course, slow that down).

The problems with epoxy or any other glue has as much to do with what you are gluing and what are you glueing to. A physical bond of any sort is always preferable to smooth, flat surfaces. One problem I've run into with using expoy to glue supermagnets to Bison tubes here in Minnesota, is that the expansion and contraction of the aluminum is different enough from the neodymium that the epoxy separates. Oh, it'll stick like the devil to whichever half of the equation it decided to bond with, but slide right off of the other.

Here's a useful FAQ that covers some of these points:

http://www.kjmagnetics.com/faq.asp

And for those of you that, like me, decide to play magnets that are so powerful that you can't separate them, here's how the pros do it: http://www.kjmagnetics.com/buildamagnetseparator.asp

One issue here is that as the rare earth magnets are allowed to snap together with a great force they may fracture and splinter or crumble.

With lesser powered magnets the mere act of one hitting another in the force they exert as they 'snap' together can sometimes cause them to be in pieces.

It is worth noting in your application that not all that may put them back together may be fully aware of this fact.

Maybe a bit of adhesive felt between the magnets would dampen the blow?

I've done a fair amount of work with rare-earth magnets (not "earth" magnets, as some call them). You can get rubber coated ones from some sources, but the rubber coating does lessen the attraction to some extent.

Yes, they are brittle and can "explode" if allowed to slam together. They can also pinch and cause blood blisters and even broken bones. And don't forget that if they pinch you, you've got to pull them apart to get that skin out. I recently bought some with 52 lbs attraction, and its all but impossible to separate them without a specialized tool.

Don't try to roughen them up. First of all, if they are chrome plated (most are) you won't have any luck. Second, if you do, you'll be removing the anti-oxidation coating, and these things corrode very quickly without it (paint or the epoxy would of course, slow that down).

The problems with epoxy or any other glue has as much to do with what you are gluing and what are you glueing to. A physical bond of any sort is always preferable to smooth, flat surfaces. One problem I've run into with using expoy to glue supermagnets to Bison tubes here in Minnesota, is that the expansion and contraction of the aluminum is different enough from the neodymium that the epoxy separates. Oh, it'll stick like the devil to whichever half of the equation it decided to bond with, but slide right off of the other.

Here's a useful FAQ that covers some of these points:

http://www.kjmagnetics.com/faq.asp

And for those of you that, like me, decide to play magnets that are so powerful that you can't separate them, here's how the pros do it: http://www.kjmagnetics.com/buildamagnetseparator.asp

Wow that faq has alot of info... thanks!

Here's an update;

I attached the magnets on to aluminum with JB weld... works great... however now that I have some handles on it the pull force is not anywhere near 60 lbs, let alone 30 lbs... its only 10 lbs, measured with a one of those scales you use for fishing ... should still be enough with what I want to do with it, but 30-40 lbs would have been much better ... I am ordering some bigger magnets from a different source and see what those do....

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