Interesting, the terms "friction" and "rolling" suggest that the small sphere is in physical contact with the larger sphere ( ie if the ball was in a fluid the common expression would be "drag"). However, you clearly state this is not an "orbit" in the traditional sense, as the magnetic force is...
But how do you search for a mathematical equation? Do you use Tex, MathML, ... I anticipate the symantic web when we will search ideas and concepts, not type setting and encodings, etc !
There are two things that bother me with Zafiratos' spectacular but arbitrary assertion. If he were using...
"Could someone introduce me some docs about the unification of electric and magnetic forces?"
-- from first entry in this topic
How about the late Chris Zafiratos' derivation of the magnetic field from the electrostatic Coulomb field:^1
\vec{F}=\frac{k q_{1}...