Thursday, October 27, 2011

Co-op Science Week 9


I spent some time talking about whys of magnets -- why do magnets act the way they do (electrons), why can we magnetize certain metals temporarily (organize the atoms in, say, an iron screw by using another magnet or an electric current), why do compasses point north (Earth has a magnetic field).

Mostly, though, we played.  I had some neodymium magnets I'd gotten at Hobby Lobby several months ago -- I'd gotten them for my refrigerator, frankly, so I can stick papers to it without having everything tumble off.  They came in packs of 2 -- a red and a yellow -- about 2 inches by 1 inch by 1/4 inch thick.  I've since figured out that they're encased in plastic because neodymium is brittle; also, the plastic keeps them from sticking together so tightly that they're impossible to pull apart (the plastic is slick enough to slide them apart).  Who knows how big the encased magnets are -- they might be much smaller.  Anyway, they're pretty powerful little goobers, and I have 4 total magnets.  I went back to Hobby Lobby recently to get more to use in class, but they were out of this particular model.

The kids were enchanted by picking up wads of paperclips with them.  Also, they're powerful enough to stick one on top of your hand and one underneath and have them stick together.

I'd taken in some iron drywall screws that we magnetized by stroking with the magnets.  Drywall screws were the only thing I could find in our workbench that worked -- most of the nails we have are galvanized or elsewise coated.  I put duct tape on the plastic of the neodymium magnets so it wouldn't be scraped off by the threads of the drywall screws.  I explained theories of how to de-magnetize the screws, but, frankly, dropping them repeatedly didn't work, and in our classroom setting  I didn't feel like messing around with heating them .

We also magnetized steel needles, taped them to small pieces of cork, and floated them in bowls of water to make our own compasses.  We discussed that these didn't have the handy marker to show us which end is north, and how could we figure out which was which? (Using our knowledge of where the sun rises and sets, for example.)  We also experimented a bit with making the compasses go wonky by exposing them to another magnetic field.

Then I got out another set of drywall screws which we wrapped in insulated copper wire like this, attaching to 9v batteries.  I had the kids work in groups for this to make it easier to supervise.

At the beginning of class I'd put a full serving of Total cereal in the blender with some water, then put it in a plastic bag.  I'd hoped to get the iron filings to separate out.  They eventually did, but this demonstration works best for me if I set one of the neodymium magnets on it for a while, then wander off and forget about it for a long time (like, hours).  At home I was able to get a dollar bill to react a bit to the magnet, but I wasn't able to in class.  The kids were somewhat appalled at the news that some people put a dollar bill in a blender to do the same type of demo ("that's illegal to do that to a dollar bill!"). Our currency is printed with a magnetic ink, by the way, which is why this would work.

I couldn't find any iron filings to use to show the poles of the magnets.  Somewhere in the house we have one of those old games where you move the iron filings on a picture to make a beard or hair, but, alas, I can't find it.  It also would've been wicked cool to get some ferrofluid to play around with, but it wasn't in the budget.

Some of the kids seemed disinterested in the entire session.  Perhaps they've done it all before; or perhaps the set up of just playing around and seeing what happened bothered them.  I'd expected that most everyone in class has played some with magnets, but now I know they've all seen certain things that we can build on as we explore more about electromagnetic forces.

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