[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.

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!