Can Nietzsche's overman be thought of as a centripetal force?
Centripetal is an adjective describing a force that brings things toward the center, not unlike the force of a black hole. Centripetal is often confused with the word centrifugal. They may begin the same way, but they mean the exact opposite.
I like the idea of opposing forces at work, in this way.
Can it be? Might that help me understand his ideal?
This actually turns out to be a general philosophy lesson, more than anything specific on Nietzsche. The real answer is "The overman can be thought of as a centripetal force if that analogy works well." You have to flesh the analogy out before any statement can be made.
In this case, Nietzsche's Übermensch is a tremendously complicated multi-faceted ideal. Comparing it to a centripetal force is like saying the Christian God can be thought of as a triangle. You are welcome to make the comparison, but you actually have to make it. You have to explain why its useful to think of it as a centripetal force. Likewise, thinking of the Christian God as the Father, Son, and Holy Spirit has value to some, and thinking of it as a triangle could have value. But in both cases, the analogy is comparing to something far simpler than the original, so you really have to explain why the comparison is valuable enough to a listener.
You say "[you] like the idea of opposing forces at work." In that case, flesh the idea out and see what these opposing forces are. See if the imagery inspires a deeper understanding of the Übermensch. If it does, great! If not, then don't force the Übermensch into a particular shape.
