Thursday, March 29, 2012


My son participated in his third-grade Science Expo last week. Each third-grader was given a blank piece of cardboard and a stapled set of instructions. Students were to come up with their own questions, which they could answer by performing experiments, researching a topic, or giving a demonstration. They then would present their projects in a big poster session in the gym, where parents, teachers, and the other grades could walk through the rows of kids and ask about their work.

The Boy’s project came out of a short video I stumbled across in the usual Internet way of a guy out on his deck dropping magnets down a copper pipe. Like any good magician, he shows his audience the two pieces separately, and then performs the trick, exploding all expectations in the process. The magnet doesn’t stick to the pipe but instead tumbles softly down into his hand.  When it came time for The Boy to settle on his topic, he remembered the video right away and wanted to go looking for the explanation.

The short clip gave us a couple of leads — neodymium, eddy currents — so that’s where we started. The magnets were easy to get off the Internet, arriving in a couple of days in a clear plastic tube wrapped in warnings. The pipe was a lot less easy to come by, oddly enough. Lots of places in town would sell us a contractor’s standard ten-foot length, but we only wanted a foot or so. After much walking and asking around, we finally found a hardware supply in Chinatown with a manager who happily opened one of his own pipe-cutter packages to accommodate us.

Once outfitted, we went for replication. Would our own neodymium magnet float down our own copper tube? Check. Even having seen the video, The Boy and I found the result hypnotic, the pleasant clink of metal on metal, the lazy drift of the stack of magnets down into his waiting palm.

Explanations pair with questions, and The Boy compiled a list of them to answer in his presentation, including:
  • Why doesn’t the magnet stick to the copper tube?
  • Why does the magnet float down the tube?
  • Does the tube have to be made of copper for the magnet to float?
  • What is an eddy current?
The idea was that he would answer these questions on his poster, include a diagram picturing what’s going on that can’t be seen, and finish with a list of Fun Facts* about magnets.

We guided him a bit, but he did most of the heavy lifting research wise. Finding information for this kind of thing used to be difficult, but now the difficulty lies in sorting and understanding information. We googled magnet- and eddy-current-related phrases and turned up all sorts of videos and cryptic equations, along with pages of physics and industrial applications, and a few fairly simple explanations. The Boy took notes. We also actually went to our local library (nostalgia!) for age-appropriate books on magnets and magnet experiments, which proved to be a mother lode of Fun Facts.

You may very well be curious about answers to The Boy’s great questions, and though I don’t have my son’s showmanship, I’m happy to oblige with grade-appropriate answers. First off, copper is not ferritic, which means magnets aren’t attracted to it. But copper is an outstanding conductor, and that’s important here. A magnetic field moving through a conductor causes electric currents called eddy currents. All electric currents have their own magnetic fields.  So gravity pulling a strong magnet (in this case, four 1” x 1/8” neodymium stacked) down the conductor triggers eddy currents, which have their own magnetic fields that repel that falling magnet, just as the same poles of any two magnets repel. The eddy currents and their magnetic fields prove fairly weak (again, in this case), which means the magnet’s progress is only impeded and not arrested altogether.

Cool, right?

The Boy insisted (before we could) on writing the text of the poster himself, first translating his notes into an explanation on paper, and then typing everything up to be printed. We spent some serious time in font selection. My lovely wife helped him with the big center diagram, though it was his idea to have a foil-wrapped magnet popup in the center. He was proud of his work, and he had good right to be.

The day of the Expo, he carried his equipment and excitement to the gym himself. It opened to parents shortly after the morning bell rang, and my lovely wife and I flooded in with all the others to check everything out. We went by The Boy first, of course, and he was all set up and ready to perplex passersby with his “Magnet Mystery” (his poster’s title). He performed his demonstration for us just as he’d practiced — first asking what we thought would happen when he dropped the magnet down the copper tube, then asking for predictions about the same magnet going down a cardboard tube, then explaining all the forces at work that confounded those predictions. Q soon came by with a pack of her classmates (all grades visited throughout the day) to listen to her brother, and he enjoyed the audience. He was truly great.**

As were so many of the kids. We know lots of families now, and we took our time hearing The Boy’s friends tell us about mass and gravity, geysers, rainbows, penguins, great white sharks, milk carton turbines, and on and on. The girl set up right next to The Boy talked through a truly unsettling experiment on the effectiveness of soap v hand sanitizer, one that involved a UV flashlight that revealed the dirt on your hands right then and there. For my part, I managed to discomfit a kid with a nice display on color vision by asking her since different creatures have different color experience what she thought the real colors were.  “I dunno,” she said, looking up the aisle and anywhere else but at me.  Sometimes I wonder why I don’t end up eating all my meals alone.

Aristotle writes that all persons by nature desire to know.*** It can be an oppressive statement if you think about it — the need to explain nagging and persistent, like an itch. And there’s so much to be known. Spring bloomed suddenly, some afternoons have been pushing 70ยบ already, and the early warmth and wet air have produced glorious morning fog.  Fog occurs when the ambient air reaches saturation, forming water droplets that reflect light, limiting visibility to at least 5/8 mile.  Copper: Chemical element name Cu; Atomic Number: 29; melting point: 1356.15K.  Celestial bodies lie in space like balls on a rubber sheet, curving space and time around them.  The body a machine, describable and flawed.  A second is equal to the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom. Consciousness is an instance of consciousness of. F = ma, except when it doesn’t.  The Boy is an isotope of my wife and I; the recipe for his making written in a billion proteins.  Q hums sweetly while brushing her teeth (though she’ll deny it) — this a fact like any other.

Anyhow, thanks to The Boy, at least one mystery is explained enough.

*Nearly every third grader’s poster included Fun Facts, where “Fun” means something like Related But Random and Interesting.  The science teacher probably suggested including them as a way to fill white space, which, given that this is likely the first public opportunity these kids had to present a poster, must have seemed positively Antarctic to most of them.
**Dare I say he was magnetic? I do dare say so, at least in a footnote.
***The opening line of his Metaphysics, usually translated as all men desire to know, but he’s dead enough to be forgiven this oversight. Also, perhaps no one better encapsulated this desire than Aristotle himself.


Nadine said...

Beautiful post, thank for sharing! You got 2 smart kids there and I love how you & your wife guide them.

Tony Dardis said...

That totally rocks. I was waiting for the 3rd grade science fair let down: "and in fact it doesn't do that" but in fact it does, and it did, and the Boy rules! I love it.

teahouse said...

Cool! I did Science Fair in junior high; I went all the way to the state championships. Good times, good times.