debug panel (F11) shows 180-200 fps, but it refresh once per second...
looking like its a computer problem: in the notebook everything fine with 500 fps.

//Once per frame is enough for slow speeds and games not demanding high precision, but for a simulation this may not be enough.
Hm, looking like you're right... on the other hand play with parameter of NewtonUpdate(), for example try NewtonUpdate(nworld, time_step / 64);