1401 Does it go up or down?

1401 Sale o scende? View larger



1401 Does it go up or down?

A sphere moves spontaneously along a horizontal variable-gauge rail, and it always moves in the same direction. Which direction? And why? If the rail is inclined, the sphere doesn’t always roll in the same direction. Why?
The explanation of these phenomena lies in the study of the position of the sphere’s centre of gravity; a good amount of physics with such a simple device.

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