This is a binary system. The velocities of the two objects are initially equal-and-opposite (object 1's velocity directed down and object 2's directed up). You might expect them to have repeating orbits, but can you explain why there is often a drift of the orbits in one direction or another? And when would you expect no drift?
Note that occasionally the objects get a bit too close and the simulation does not handle the physics with enough accuracy to really reproduce the orbits accurately.
Simulation written by Andrew Duffy, and first posted on 5-12-2018.
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