2 magnifying lenses

[Kreon]

I have 2 magnifying glasses. They are basically plastic frames that rest on the paper you're trying to magnify that support a lense about and inch and a half in the air. Don't know where there'd be a picture... sorry

One of them has a chunk from the bottom missing. The other doesn't. When I spin the unbroken one into the air (by grasping around the lense adn spinning it into the air). The axis of rotation is the center of the lense.

When I use the borken one, it gets way of kilter, adn teh axis of rotation is off...

Why does it do this? Is it becasue of teh missing quarter messing with the distribution of mass?

Sorry my descrpitions aren't that good, I hope you get the idea

Thanks

 

[Calin]

When you start rotating an object, when there are no other forces applied, it will rotate around the center of mass. If the forces applied are equalizing themselves, the object will rotate around the center of mass too. Try to rotate a pen around one end, and let it fly. It will fly away with the speed it center of mass had, and it will rotate around the center of mass. Same with a frisbee - when you launch it, it has a complicated trajectory (mostly translation in one axis, and rotation around the edge where you hold it). Once you launch it, there will be a translation (forward movement), and rotation around the center. If you have a frisbee with holes in it (and not a disk), put a heavy weight on the edge - once you throw it, it will "wobble"