Crossroads

A fun and clever puzzle.  You should find it fairly easy to manipulate the balls to the center positions as we have made some depressed landing areas there, but the outside may be more of a challenge…. whatever way you tilt the puzzle seems to cause at least one of the balls to move away from the outside….hmmmm, such a problem.

But, there is a very elegant and quick solution that involves using a scientific principal.  Can you find it?