The red sphere is linked to its starting position and at the same time to three lightblue spheres (top left) which are fixed to their locations. The yellow arrow points to the equilibrium location to which the red sphere will move. (follow the sequence rowwise from top left)
A second image shows the effect of forces of different strength; the link to the left lightblue sphere is threetimes as large as in the first example.
Compare the two equilibrium solutions (bottom right) for the red sphere !