[quote author=Fu-Kwun Hwang link=topic=173.msg5398#msg5398 date=1265885394]
If the center of gravity for those two objects is (xc,yc) and the supporting point is (x,y)
The conditions for stable equilibrium is (x=xc and y>yc) when supporting bar is horizontal.

The who system can be model like a pendulum, the supporting point is the tip of the pendulum, and assume all the mass is located at the center of the gravity.
[/quote]

This is amazing insight, thanks for the tips, looks like i need to change quite a bit of evolution equation....LOL
will remember your tips! thx!