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Angular momentum is a measure of the momentum of an object that is spinning. The direction of the angular momentum vector h of a spinning object is parallel to the axis of spin, as shown in figure 5. For any independent collection of spinning objects, the total angular momentum must stay constant. This is known as the conservation of angular momentum. |
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Figure 6a: Holding the
gyroscope horizontally. |
Conservation of angular momentum can easily be observed if you sit on a swivelly chair while holding a spinning gyroscope. The chair is mounted on a pivot so that the chair can rotate about the vertical axis. If you hold the gyroscope so that its axis of rotation is horizontal (so that the spinning disc is in the vertical plane), the gyroscope's angular momentum is in the horizontal plane and there is none in the vertical plane (as in figure 5). |
| If you now tilt the gyroscope to the vertical, so that its spinning disc is in the horizontal plane, you have transferred its angular momentum to the vertical plane. Since the net angular momentum in this plane must remain zero (to conserve angular momentum - it was zero in this plane when we started) you'll find that you and the chair start spinning to compensate! You will, of course, move in the opposite direction to the spinning disc. |
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If you move the gyroscope back to the original position, your spin will again cease. Turn it vertically the other way, and you'll spin in the other direction. Enough to make anybody dizzy! This is a really fun experiment to do and it works really well if you're skinny - less than 8 stone and you'll spin really fast!
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Argomento estratto dalla pagina web
http://plus.maths.org/issue7/features/gyroscopes/
