Algodoo

Press up to activate. Scene speed is 0.01x to make process visible, but works at 1x.
Slight modification of my jump drive.
Engine itself is stationary so rounding errors doesn't apply to it.
Acceleration phase has now 4 1/100 second steps, because 1 step acceleration was impossible due to forces becoming NAN and deleting objects.

Engine accelerates things to 120% speed of light, and then decelerates to almost 0 (under 100m/s). All ABC collision objects in the scene are affected.