Here is [my note on mechanics of a free particle](http://febdian.net/files/download/[diary]_mechanics_of_free_particle.pdf “click to download!”). The note is based on my lecture in [Relativistic Quantum Mechanics](http://tinyurl.com/j3ccm) two years ago. Nice course, nice lecture, I really like it. The aim of the calculation is to determine the equation of motion of a free particle. We assume that the free particle is point-like particle and spinless. In the end, we have Schrodinger equation for non-relativistic case and Klein-Gordon for relativistic...