Sunday, 30 January 2011
The spinning table
Can you predict what will happen to the objects placed on the spinning table?
First roll an object across the table by beginning the roll on the spinning table itself. Then try to set the object rolling onto the table from the peripheral area around it. You can use the buttons to adjust the speed of rotation.
The object will always circle in the same direction as the spinning motion of the base below it. An object that is set to roll before it enters the spinning table will roll off the table at nearly the same spot and heading in the same direction as it would have done if the table had not been spinning. The object that is set to roll directly on the spinning table will behave unpredictably.
A frictional force begins to affect the object as soon as it enters the spinning table. As the object passes over the centre of the spinning table, the direction of the friction changes to follow the direction of the spinning. Therefore, when crossing over the entire spinning table, the object is affected by an equal friction in both directions, left and right. Thus, when reaching the stationary part of the table, the object continues its path in its original direction. The friction on an object that is set to roll directly on the spinning table does not have this same symmetry. Thus, it will behave unpredictably.
The same phenomenon is illustrated, for example, when you jump off of a spinning carousel. If you want to land in one specific spot on the ground and stay there, you must resist the spin of the carousel and jump against the rotational direction. It would be, however, a great deal easier to continue in the same direction as the spinning motion and to take a few running steps upon landing on the ground, in other words, not to resist the inertia.