I am a bit confused about something! Exactly under what kind of transformations are scalars invariant in the domain of classical mechanics? The fact which is disturbing me is, say we have a moving body of certain kinetic energy in a certain inertial frame of ref, and then we choose to.observe it from a different inertial frame moving with a certain velocity w.r.t the frst one. The kinetic emergy of the body is certainly not invariant? So are scalars not invariant under translations and boosts( not.sure if it can be called so within the classical domain) ???