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Nov26-12, 08:28 AM
P: 28
I knew it would be hard, sorry. Let me phrase it in a simple way.
There is a disc with a hole (I recently posted here asking for its moment of inertia). It is spinning about an axis passing through its own diameter. Due to the shift in point of contact and center of mass the disc scratches the ground and this friction creates a torque opposing the angular frequency. (angular momentum in the direction). this opposing is happening when the center of mass is on the bottom. This friction will also bring the center of mass upwards (like a tippie top) till the line of center of mass co-incides with the sliding point.
Now friction decreases, angular frequency goes back to normal and meanwhile a change in radial vector also occured. (from center of mass to diameter minus center of mass).

how can all these changes expressed in an equation.