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Q & A: uneven rotation of magnets

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Most recent answer: 08/07/2015
Q:
While I was doing some experiments with magnet, I noticed something that I want to ask and confirm my observation. I hanged a magnet and left it freely. First I tied it with thread and set it to hanging. It immediately started spinning. But then my father pointed out that this spin might be due to these twists of thread. And certainly it confirmed my doubts (may be you want to call it torque). This spin motion was indeed due to twists of the thread (because magnets have some weight, so as I hanged it, it opened those twists �Google it �thread twists��). But then I replaced it with a single fiber like thread (single, no twists). And indeed I found no spin motion at all, but it stood in air pointing the South Pole towards north and vice versa. Then I spun it and again set it free. So it was spinning. As we know there can be two kinds of spin motions, clockwise or anti-clockwise. So here is what I noticed, �IF YOU GRAB THREAD IN YOUR LEFT HAND THEN THE THUMB POINTS IN UPWARD DIRECTION AND THE CURLED FINGERS DESCRIBE THE INITIAL SPIN MOTION OF MAGNET (THE MOTION IS HENCE CLOCKWISE). NOW CHANGE THE HAND AND GRAB IT IN RIGHT HAND, SO THE CURLED FINGER DESCRIBE ANTICLOCKWISE MOTION OF MAGNETS.There is some difference between these motions. When the magnet spins in clockwise direction, its motion is smooth but when it gradually slows and eventually stops and reverses the spin motion it looks like it hesitates in doing so. My question is about this hesitation in anti-clockwise spin of magnets. Were my observations correct or did any mistakes. If you perform and inform me would be great help. I know it�s not great experiment but at least give it a shot, if already have performed share it. Thanks! @HalarTalpur
- Halar (age 20)
Pakistan
A:

It's great to hear of people doing experiments. There is a possible reason for a bit of unevenness in the magnet's rotation. The earth's field exerts a torque on the magnet, just as it does on the little magnet ion a compass. SO the magnet's rotation could speed up a little as its north pole turns toward the north and slow down a little as it turns toward the south. That effect would happen regardless of whether the magnet were turning clockwise or counterclockwise. It may be an accident that you happened to notice it more one way than the other.

Or perhaps there's some kinking up of the thread. That could exert a torque (as you noticed in the first experiments) and maybe that would go differently for big CW and CCW twists. That sort of effect would happen even if the magnet were replaced with a non-magnetic bar.

Mike W.


(published on 08/07/2015)

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