I’ve been looking for some magnets for a project I am working on, and I am pretty disappointed in how the search is going. I’m trying to find some magnets that I could assemble in a ring shape, that would hold a smaller magnet centered above the ring. After purchasing and returning some magnets from home depot that weren’t strong enough I began wondering why there is no measure for magnetism (that I know of). From what I can tell, it seems the strength of a magnet is determined by the material it is made out of, and how much of it there is. If that is true, why aren’t they labeled “100 magnetopowers per 1 gram of magnet” and if you had a 5 gram magnet, you would know had 500 magnetopowers!
Also, does the shape of a magnet make a difference in its strength? For example, would a cylinder be stronger than a disk? A horseshoe more than a cube? Thanks!
Magnetic field strength is measured in teslas or gauss (Wikipedia links).
As to strength of various magnets, the material used and the amount of it are the important criteria. The shape of the magnet is determined by its application. A disc shape may be more useful than a bar or horseshoe for a given use, but won’t have an appreciable effect on it’s strength.
For very powerful magnets, look for rare earth magnets. These are quite small and quite strong.
I don’t quite understand what you are trying to build. When you say that the magnet ring will hold a smaller magnet above the ring do you mean suspended in mid air without restraint?
One problem I see with your ring is that the magnetic field will be confined to the ring. In order for a magnet to do anything there needs to be an air gap in order to make the field accessible outside the magnet.
In addition. if you do mean that the small magnet would be suspended in the air, I think that’s an unstable condition. It’s like standing a pencil on the point.
I’m trying to build a flat wooden box, with the ring of magnets inside it. Then I wanted to make a smaller wooden box with the small magnet(s) inside it, and hopefully be able to suspend this in air above the ring of magnets.
I read them and learned a lot, but I still don’t understand why they wouldn’t label the packaging of any magnets with their strength? One of the wikipedia articles mentioned that they can become saturated. Is it difficult to get magnets with the same power? Or is it just too difficult/expensive/time consuming to actually measure?
Well, it would work, if only he could find some room temperature superconductor material.
To the OP, magnets I have purchased were rated in pounds. I assume this means how many pounds of pull are required to remove the magnet from something - or how many pounds they would hold up. I recently purchased some 5 lb. magnets that are about the size of a watch battery. They will jump off the table to stick to each other from a distance of about 2 inches. Larger (more powerful) magnets were also available.
Also, as David Simmons pointed out, your design as described isn’t stable. The ‘floating’ magnet will tend to simply flip over and crash into the other magnets. However, if you are trying to suspend an object magnetically, that’s a do-able thing. Google magnetic bearings or magnetic levitation for examples.
Just for laughs, can you make the lower box’s top concave and the upper box’s bottom convex? This might help stabilize your apparatus, since I’ve seen from my own amateur experiments that trying to balance a magnet on top of another in hopes of making it hover is enjoyable for about the fiftieth of a second the floating magnet takes to slide off to the side and flip over, beaten only by Paris Hilton for eagerness and agility.
Why not? If it works I’ll try anything! I think I’m going to have to buy the magnets online, but by the time I get them hopefully I will be all set up.
There is a magnetic toy involving a spinning magnet suspended in mid-air over four other magnets. And there is a range of designer furniture that is magnetically suspended and stabilised (I assume that this does not involve moving parts).
You can arrange several magnets to produce a one-sided magnet (field lines on one side only) which may help. You have to create stable points of inflection in the fields.
As has been mentioned above, a stationary magnet supported by magnets beneath it is, I’ve been told, an unstable situation. There are toys where you put a spinning magnet above other ones and it’s supposed to be stable. si_blakely mentions one. I got another several years ago for Christmas, buyt I stioll haven’t succeeded in making it spin stably in position.
I’ve seen much easier methods of magnetic suspension – I have a pen holder with a magnet on top pulling the (very light) pen against gravity. It’s very stable (although easily upset). I also have a set of doughnut-shaped magnets that will hold each other up if you place them on a common axis through their center holes (like a pencil).
By the way, they manufacture devices for measuring the sttrength of a magnetic field, called (appropriately) gaussmeters. One reason they probably don’t give a measure of the magnetic field for magnets you purchae is that it varies considerably with distance from the magnet, and with direction. You only get reasonably constant magnetic fields in special constructions like solenoids. There’s also probably an enormous variation in the properties of a batch of magnets, so even if you specified “field in the x-diection at the center of the face 5 mm away”, it would be very different from magnet to magnet in your set. And nobody cares about the actual force, anyway, so why bother?
>In addition. if you do mean that the small magnet would be suspended in the air, I think that’s an unstable condition. It’s like standing a pencil on the point.
It’s impossible to use magnets alone to do this suspension. You can do it with a superconductor as noted above. You can also do it with active control systems that use electrical power and some kind of distance regulation device (the control system has greater positive stability than the magnets have negative).
You can levitate a magnet with no moving parts or connections or superconductors or control systems if you also use diamagnetic materials. Diamagnetism is weak, but detectable - why, just this morning I used a row of NIB magnets on a steel strip to push a bismuth bar pendulum an inch or so out of verticle. At kjmagnetics.com you can buy a pretty little wooden stand that does this. It uses graphite for the diamagnetic material to create stability, and an overhead magnet a couple inches away to provide approximate (though unstable) cancellation of the floating magnet’s weight. They also sell NIB (neodymium iron born) magnets, which are the strongest permanent magnets made, and are surprisingly affordable. You can read about “energy density product” (IIRC) there.
Some of the most powerful magnets I’ve come across are inside hard drives - a pinch between two of those suckers can really hurt. You might want to see if you can get some old hard drives cheap and use those.
