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Unexplained Project

  1. Jul 12, 2007 #1
    March 19, 2007

    About a month ago, I was filling some spare time in class by playing around with two ball point pens. I made some observations that turned into a class science project in physics.

    Both pens are about six inches long. One ball point pen is a common retractable pen with a steel point and plastic casing. The second ball point pen has some unique features. The casing is made of rubber. The half of the pen opposite the point is very flexible and has a button magnet affixed to it. This end has enough flexibility to allow the pen to hang straight down if the magnet is attached to a refrigerator door. In fact, the pen was designed for this purpose.

    While playing with the pens, I attached the common pen to the flexible rubber pen by attaching the steel point to the magnet on the flexible pen. I found that by holding the flexible pen by the point, the power of the magnet on the opposite end was just strong enough to overcome the force of gravity and hold the common pen suspended from it.

    With the two pens attached in this manner and hanging straight down, I began to twirl the rubber pen in a circular motion. Doing this caused the flexible end of the rubber pen and the attached pen to move in a circle. The attached pen was no longer hanging vertically because the circular force of the twirling motion was causing it to try to rise to a horizontal position.

    Now a very interesting thing happened. When I stopped the twirling motion, the two pens returned to their original vertical position with the common pen still attached to the magnet on the flexible pen. The flexible pen was now rigid and was not moving (not twirling or rotating), but the common pen continued to rotate at a rather high rate for a considerable time. I found that I was able to reproduce this result every time I repeated the procedure. The most remarkable outcome of my experimentation was that THE COMMON PEN ROTATED IN THE OPPOSITE DIRECTION OF THE TWIRLING CIRCULAR MOTION. In other words, if I twirled the flexible pen clockwise, the common pen rotated counter-clockwise when I stopped the twirling motion. If I twirled the flexible pen counter-clockwise, the common pen rotated clockwise.

    I thought about what I had seen and at first thought that I had caused the steel parts of the common pen to become magnetized and had somehow set up a magnetic field which was responsible for the rotational motion of the common pen. I quickly eliminated this hypothesis by testing the common pen and found that it had not acquired magnetic properties.

    After more careful consideration and research into the Laws of Motion, I arrived at the following conclusions:

    1. I had previously studied the effects of friction between two surfaces. It would appear that the connection between the small point of the common pen and the magnet of the flexible pen would have an extremely small coefficient of friction. This would allow the observation of Newton’s First Law.

    2. Newton’s First law of Motion (Law of Inertia): Every object in a uniform state of motion tends to remain in that state of motion unless an external force is applied to it.

    In this case the common pen would be free to rotate until the small amount of friction and the pull of gravity brings it to a stop.

    3. Newton’s Third Law of Motion: For every action there is an equal and opposite reaction.

    It appears to me that the circular motion that I have input into the flexible pen has somehow created an equal and opposite motion in the common pen. This would account for the rotation in the opposite direction.

    All of the above brings me to the reason for asking for your help. Since the connection between the point of the common pen and the magnet of the flexible pen is very small, what is causing the circular motion of the flexible pen to be transferred to the common pen to set up the equal and opposite reaction?

    And one more thing: the common pen does not have a spring that sheathes itself. I don’t see how my twirling motion could then, in effect, cause the writing element to rotate. I am not simply winding up a pen and casing it to unwind. Any explanation?
  2. jcsd
  3. Jul 12, 2007 #2
    There was a magnetic apparatus, consisting of two magnets mounted on a bearing in a board, if you rotate one, the other will rotate in the opposite direction.

    It can also be demonstrated by using speaker magnets (those donut shape magnets). Have one stand on it's edge so it can roll or rotate freely, have the other do the same a distance from the first but should be affected by the magnetic field (so the north and south poles are facing each other- the poles are on either side of the donut or disc magnet). Rotate the first, and the second magnet will also rotate in the opposite direction.

    See that my example above, when you rotate the first, The pole of one magnet will try to seek the opposite of the other in every orientation, so it will be forced to rotate with or against the magnet. It's hard to explain in words, but mark the poles with an obvious sign and you'll see.

    When you use pens, the other one is doesn't have a magnet. but it can be easily magnetized and have defined poles by just spinning it against a strong magnetic field. I've actually 'remagnetized' 'dead' compasses in this manner or even reverse it's orientation:smile:

    You could also use a compass and a bar magnet to see it more clearly. But make sure the bar magnet is kept a good distance from the compass so you won't be reversing it.
    Last edited: Jul 12, 2007
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