1. One of my freind showed me this interesting thing.
When we hold a small sphere shaped object ( like toys or stones) between
our 2 thumbs lightly(With one thumb over the other, object between them), the object rotates.
I didn't understand how this happens. Anybody can try it out and if reason is found please let me know.

2.

3. By rotating I assume you mean that it spins in a direction perpendicular to your thumbs and not across them.

What you're doing, and this is true with not only spherical objects but any object that has a place you can attach to, is that you're concentrating the area to which the object rests into less of a plane and more of a point, giving it an axis.

If it appears to start spinning spontaneously it's because either you unwittingly moved enogh to start making it spin, or the object is slightly irregular, lobsided, it as the force of gravity pulls on the heavy side the object will rotate so that the heavy side of the object is closest to the ground. This is true also if your axis, fingers, aren't exactly in the center of the object and the "half" with more mass will move to the bottom.

The same thing will happen with a box, or a rock... anything that you can hold well enough to make the plane it is resting on concentrate to a point.

The same thing happens with a plate spinning on a bar. If you try to spin it on a table it won't. If you put it on the top of a bar and spin, hopefully in the middle so you won't break the plate, the plate will spin.

I hope that makes sense, and if you want me to get more technical I can. I don't know who mathematically inclined you are. This is much more the realm of physics than Earth Science.

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