Lagrange constraint mechanics problem

[DylanG]

http://img221.imageshack.us/img221/3754/capturetp.png

Just a simple question. I can see that for this to work I need:

T_rot = 1/5 ma²(thetaDOT + phiDOT)²

Just can't work out what phi has to do with rotational kinetic energy. I would have thought it would need to be simply the same thing but without the phiDOT term.

 

[diazona]

\theta is the angular position of an identified point on the smaller sphere, measured with respect to the line joining the centers of the two spheres, right? Note that not only does \theta change with time, but so does the orientation of that joining line, so you need to take that into account as well. That's where the \dot\phi comes from.