More magnets

The mysterious Professor X, from that post the other day about scaling up little toy sculpture magnet things to evade bans on such toys, has contacted me again:

Now that I'm not headed to bed and can really read the post, thanks again for such thorough and useful info. The comment to your post was useful, too.

I assume that if the sphere size stays the same and the flux factor goes down, they're just not going to be as effective for sculpting because they won't hold as well, and they won't have the same satisfying snap, etc. The lack of a workable alternative is just as good for me as a teaching point as a workable alternative would be; I'll have fun with this. I appreciate your assistance to total stranger.

I find it funny, after reading your post, that the CPSC in its Notice of Proposed Rulemaking says, "Thus, it might be possible for manufacturers to make magnet sets that contain strong magnets so long as the magnets are sufficiently large, although the large size could reduce their utility."

Well, that's an understatement, apparently.

Professor X

Various magnets

To get a, literal, feel for how these things behave, I do strongly recommend you hit eBay and get some cheap magnets there, both the little strong silver ones and the black shiny "rattlesnake egg" type (which can be had as spheres as well as elongated ovals).

The eBay seller I got some of my element samples from, "The Mists of Avalon" (here on eBay Australia, here on eBay UK) has some interesting magnets too, including irregular "tumblie" versions of the rattlesnake-egg type.

Plus, of course, these things really are some of the greatest fiddle-toys ever created. Just don't put them in the same pocket as your credit cards!

I used to also have to warn people to keep strong magnets away from CRT monitors and TVs, but that's way less of a problem these days, of course. To demonstrate rare-earth magnets' their ability to wipe other magnetised things, get a standard flexible rubber fridge magnet of the sort given away as promotional items, scrub it all over with a smallish rare-earth magnet, and behold that it now can't stick to a fridge at all.

This is because those rubbery magnets are set up with a "one sided" array of alternating parallel rows of magnetisation - that's why only one side of them sticks to the fridge, and also why they stick to each other in such an odd, "lumpy" way.

Fridge magnet field pattern

You can also use magnetic field viewing film (a small piece of which can be yours for less than $10 delivered) to see this oddness directly.

When a strong enough external field re-aligns these parallel poles so they all go one way, the essentially feeble magnetic material can no longer hold up own weight.


There's a lot to be said for ferrofluid, too.

The cheapest ferrofluid on eBay is in tiny squeeze sachets, for topping up the coolant in tweeters. But you can get thirty grams for less than $US25 delivered; that's enough to have some fun with.

There are also several dealers selling sealed vials with ferrofluid and possibly also some immiscible liquid inside, to keep the ferrofluid clean and, perhaps more importantly, prevent other objects, people and pets from being stained by it. Regrettably, you can only get some of a ferrofluid stain out of your clothes with a magnet.

Also, if physics demonstrations at all interest you, those little magnets can be great for those, too!

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