Two bodies that attract each other gravitationally will move in a conic trajectory with respect to the center of mass of both. A conic is the meeting of a cone and a plane thus it is always a plane movement with respect to the center of mass of the system. My question is: does this plane pass thr...

It seems to me that a frame of an observer undergoing free fall on Earth (before entering its exosphere) is not inertial in Newtonian mechanics, even though it is inertial in special and general relativity, according to this question and this physicsforums thread. I still don't fully understand w...

The generic definition of a symmetry in terms of an action is simply some transformation leaving the action invariant. If we have some configuration space $\mathrm{Conf}$, for instance for a point particle \begin{equation} \mathrm{Conf} = C^\infty(\mathbb{R}, \mathbb{R}^n) \end{equation} and the ...