Re: Physics Simulation Mentor comments: This thread was split from an OLD thread that was inadvertently resurrected from the dead. The original thread is [thread]182831[/thread]. Out of curiosity, do you mean to basic Verlet or the Velocity Verlet? I've been doing something like the OP's simulation using the velocity Verlet, and yes, it seems to preserve energy pretty nicely...but I've noticed that elliptical orbits tend to show "apsidal precession" (like Mercury's orbit tracing out a rosette) ... which they shouldn't in a purely classical simulation, right? Are there any common errors that lead to this, or corrections to deal with it? Or is it an unavoidable artifact of using discrete timesteps? Thanks!