Hi all, First of all, sorry for not using the template, but I think in this situation it's better to explain my problem right away: I'm studying for a physics test, but I think I don't really understand Galilean invariance. In my textbook there is an example in which they proof that if you consider 2 frames S and S' in standard configuration that the second law of Newton is Galilean invariant by proofing that if [itex]x' = x - Vt[/itex] than [itex]F_x = F'_x[/itex], so this law holds in both frames. So far I understand this. However, in the book there is one assignment in which they ask me to verify that the relationship between kinetic energy and momentum, [itex]E = p^2/2m[/itex], is Galilean invariant. I couldn't really figure it out by myself so I looked at the answers. The answer is as followed: Source: McComb, W. D., 1999. Dynamics and Relativity. New York: Oxford University Press Inc. I understand all of the equations, however I just don't understand why this verifies that this relationship is Galilean invariant. Can someone explain this to me? Thanks!