acceleration

I'm always curious about questions like this. Since the answer is obvious, why ask it?

Also, the answer isn't obvious. The question speaks of "motion." Does this require "unbalanced force."? Usually, it does. Like in a tug-of-war. But suppose you're just a particle in space and something bumps into you. Is that "unbalanced force?"

Yes.

When one force is greater then the other.

forces can be unbalanced because they are at differant hights there fore they are not at equal hights so they are unbalanced.