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What makes magnets work?
May 8, 2014 7:54 AM   Subscribe

My second grader is doing a presentation on magnets. He's read books and can tell you all sorts of cool things about magnets, which is probably fine for second grade. But the really interesting question is not "what do they do?", but "why do they do it?" Can anyone explain how magnets work at a level second graders might understand?
posted by squaregear to Science & Nature (10 answers total) 10 users marked this as a favorite
 
It's an incredibly hard thing to answer in a way that is both (a) correct, and (b) aimed at an appropriate level.

You're not going to want to introduce the concept of electrons, let alone the Pauli exclusion principle. The standard kid-level explanation is usually in terms of certain metals consisting of a jumble of 'domains' which act like tiny magnets. Only when these domains are brought into line does the metal object become a 'magnet'. An analogy would be people all pushing an object in different directions vs. everyone pushing together in the same direction. But you still haven't explained why the forces of attraction and repulsion exist - for those you've got to introduce the idea of an invisible field around the magnet - something probably best illustrated visually (iron filings etc.) than by analogy.

The 'why' questions are always the difficult ones, because each 'why' tends to lead to half a dozen more 'why's, and before long you're into quantum mechanics.
posted by pipeski at 8:08 AM on May 8 [1 favorite]


Richard Feynman was famously asked: What's going on between these two bits of metal?

The explanation is suitable for all ages.
posted by odinsdream at 8:20 AM on May 8 [5 favorites]


The simplest thing to say is probably that everything is actually full of tiny magnets,* but they are only strong enough to feel when a lot of them get together and point in the same direction, and that only happens in a few metals. I agree that visual demos are great, and very easy to make for this topic. I did a presentation on magnets when I was in third grade. I brought the usual iron filings demo and also an electromagnet cobbled out of a large nail, a little wire, and a lantern battery, with a switch made out of a paperclip. It was a hit.

*namely, electrons, but as pipeski says that's maybe worth leaving out. Why the electrons in iron like to align but those in glass or whatever else don't doesn't really have a second-grade answer as far as I know.
posted by Aquinas at 8:20 AM on May 8 [2 favorites]


Even at the quantum-mechanical level, magnetism mostly boils down to "just because".

I think I would go with an explanation along pipeski's lines:

- Macroscopic magentism comes from cooperative effects among tiny microscopic magnets.
- The tiny magnets just *are* - they have a characteristic (you can call it spin if you want) just like your second grader has eyes of a certain color and hair of a certain texture.
- Once you get a bunch of tiny magnets in a group, and they get a little bit organized, it is a lot harder for any of them to get out of line (think how hard it is to suddenly walk backwards if you're walking along holding hands with people on either side of you)
posted by janell at 8:22 AM on May 8


I asked a similar question a few months back and the basic answer is that there is no good way to explain magnetism in layman's terms since it essentially boils down to "magnetic things are magnetic".

I was just going to link the Feynman video but I see that odinsdream has beat me to it. It may give you a good idea of why this is so difficult to answer.

The best explanation I can think of for that age group is that an object that is magnetic consists of lots of little magnets that are all pointing in the same direction. If you're unlucky, the next question will be "but what are the little magnets made of", in which case you are entering "turtles all the way down" territory...
posted by oclipa at 8:24 AM on May 8 [1 favorite]


I'd start by taking a step back and say that sometimes things look different when you look at them very very closely than when you look at them from far away.

For example, look at a TV screen or a monitor with a magnifying glass, and you can see the individual elements making up the pixels. From far away, it looks like a single image -- say, a face, but when you get close, you can see that the single image is made up of tinier objects that have a different structure than you might expect.

Matter is like that. From far away, an object, say, a hunk of iron, looks like a single lump. But if you look very close, you see a different structure: atoms.

Different atoms have different properties. In some sense, you can think of them as little balls that spin around (they're not literally spinning, but it's a good analogy), and they tug on each other and push each other around in various ways. One of the ways that they tug/push each other has to do with the atoms spin: if they are spinning in the same direction, they tug; if they are spinning in opposite directions, they push away from each other. (Again, oversimplification, but good enough...)

Just like the pixels in the picture, you won't notice this property from far away. All these atoms are tugging and pushing each other like a big chaotic crowd at a party.

But what happens if you manage to get all the atoms facing in the same direction, kind of like getting everyone in a crowd to face the same direction? They'll all tug/push together in the same direction. This makes it become a strong effect -- and you might be able to feel the effect from far away. That's what happens in a bar/horseshoe/refrigerator magnet.

Now, if you take a magnet and rub a needle over and over in one direction, you're essentially applying tugs to orient the atoms in the same direction -- kind of like telling the crowd all to face one way. The needle becomes magnetic.

Conversely, you can take a magnet -- in which the atoms are oriented the same way -- and cause them to be disordered by heating the magnet hot enough. (The jiggling motion of atoms goes up as temperature goes up, and above a certain temperature, the order of the magnet is defeated by the disorder of the heating, and the magnet loses its magnetism.)

How strongly the atoms feel the tug and push of a magnet is different from atom to atom. Iron tends to feel it very strongly. Other atoms, like oxygen, don't feel it as much (but they do feel it to some extent... you just need a stronger magnetic field to see oxygen's magnetism [technically, paramagnetism].) With a strong enough magnetic field, you can even force an animal's atoms to respond to the tug. See, for example this link. (youtube) [Technically diamagnetism.]

A bit of handwaving, but decently accurate... and something a 2nd grader can understand.
posted by cgs06 at 9:03 AM on May 8 [8 favorites]


"Of course it's a reasonable question. It's an excellent question, okay?"

All I can do is offer a third vote for the Feynman response. You should at least listen to it the whole way through for yourself, and notice how he spends more than half of the time not answering the basic question.

Basically, all matter is made of tiny magnets, and when these tiny magnets are all lined up in a thing, the thing itself is magnetic.

Somewhat more accurately, a charged particle creates electromagnetic fields - electric fields are the familiar things that drive electricity down wires, for example, and magnetic fields are created when a charged particle moves. Gravity and electromagnetism are the two forces that explain almost everything in daily life, but they don't have a deeper "why" so far.

(There are two others, the weak force - which is weak, and relevant only for radioactive decay in regular life, and the strong force, which is relevant at the scale of the atomic nucleus - ever wonder how all the positively charged protons can hang out with each other in the tiny atomic nucleus without flying apart from electromagnetic repulsion?)
posted by RedOrGreen at 9:16 AM on May 8


If you get 2 groups of magnets together and the 2 groups face each other -- they want a group hug.

Now split the kids into two groups. Have them look every which way but stand still. Then tell each group to look at the other group, and yell "GROUP HUG!!!!"

Why do they do it? *shrug* When you're talking about magnets, the heart wants what the heart wants.
posted by vitabellosi at 9:26 AM on May 8 [1 favorite]


All I can do is offer a third vote for the Feynman response. You should at least listen to it the whole way through for yourself, and notice how he spends more than half of the time not answering the basic question.

The whole thing is great, but for me the a-ha moment is when he points out that you aren't at all curious or surprised about why the chair pushes back on your hand, but it's super mysterious all the sudden when magnets do it. Literally putting your hand on a table and realizing you're feeling billions of electromagnetic moments is a crazy cool thing.
posted by odinsdream at 10:09 AM on May 8 [2 favorites]


Not sure if relevant, but this whole discussion reminds me of a passage from Kim Stanley Robinson Mars Trilogy that goes something like this:

A famous physicist (who is largely responsible for starting and guiding the terraforming of Mars) is teaching a group of students physics. These are very bright children, all descendants of the handpicked first 100 mars colonists, who figure out a fun game to play with him (his name is Saxifrage Russel IIRC).

The start asking him why? when he was teaching them about some aspect of physics, such as gravity or optics or whatever like that and then follow that with more whys until they reach the end point of him stating, that is just the way stuff fell out at the big bang (meaning chaotic origin of the universe) ending his train of whys and signifying that the children have won and he doesn't know everything, or to put it another way, ultimately it is the result of natural laws of matter (i.e. physics) that are more descriptive than determinitive, and why? isn't really a meaningful way of pursing the knowledge for a physicist. And anyway most people mean how when they ask why about these kind of things anyway.

Of course the passage by Richard Feynman sums it up pretty well...
posted by bartonlong at 11:23 AM on May 8


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