The magnetic moment of a flat current-carrying loop (current = I), area = A) is IA The magnetic moment is a vector quantity that points along the field line perpendicular to the plane of the loop. In terms of the magnetic moment, the torque on a flat coil with N loops in a magnetic field B is

τ = N · (IA) · B sin θ,

where θ is the angle between the field and the magnetic moment vector.

So. This is where it started. It's where it ended, too, but let's forget about that this time around and focus on the beginnings; fresher that way. Keep your eyes on the crest of the hill (and then the next one...and the next...) and try to keep your feet under you as you go skipping down into the valley, avoid the rocks just waiting for the right moment to come jumping off the ground to nail you in the forehead and try not to feel too jubilant. Easier to be floored by majesty when you've never had a really wonderful day. Good to not have ever been apathetic, too, but you know. Having once been apathetic makes it easier to smile at things, day to day. Having been ecstatic makes it easier to frown as well as being a magnet for nostalgia.

Speaking of magnets: they were the beginning. She was sitting cross-legged on the floor at a low table in the kids section of the local library. It was late at night, later than any kid would ever be out, and she was alone, just her and a set of magnets. She was playing with them, little round ones, painted in primary colors, attracting and repulsing each other like magnets are supposed to do. It seemed to me that bouncing the things off of each other would get old fast, but she was totally involved in what she was doing. Play with them enough and one day you might get to play with the huge ones, the ones that drive trains and power cities and accelerate particles to close to the speed of light. Until the Department of Defense lets you cause brownouts throughout the entire pacific northeast in the name of Science, you have to make do with seeing how many sheets of paper you can stick to the fridge at a time.

I was just grateful she wasn't defragging my hard drive by hand.

What she was doing was this: she had two magnets, about the size of pennies but thicker, and a ceramic bowl. One magnet was on the table and the other was hovering above it, pressing against her thumb and trying desperately to either escape or flip over, whichever was easier from moment to moment. When the top magnet slipped in a suitable direction she did something I couldn't see with her thumbnail and flipped it high into the air, higher than it was supposed to go if it was following the rules. The bright red magnet spun - I want to say it did so lazily and compare the thing to a flipping coin but there was a certain frantic quality to the rotating lump of iron that negated the metaphor - and landed with a vaguely metallic clunk in the bowl. Without so much as blinking she reached for another magnet and started again.

We did many things over the coming years but they all slid back to this, my first sight of her. I think it was the way she so casually meddled with forces I couldn't begin to understand that held such a power over me, or maybe it was the sheer weight of her focus. Either way - the last magnet I have any recollection of her flipping into the air I was sitting on top of.

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