Hey all! I always use this principle when I do exercises, but today I found out, that I can't explain why it's valid. What I'm talking about is that when you apply a torque to a free object it will always start to rotate around it's center of mass rather than just an arbitrary point. Why is that? I know that rotation around the cm requires the least energy so if there was some fundamental theorem saying that a system always tends towards the least increase in energy or whatever, that might explain it. Yet I don't think that's the way to go, so can someone explain it please?