1. The problem statement, all variables and given/known data Massive particles are relativistic when their kinetic energy is comparable to or greater than the energy corresponding to their rest mass. (This condition implies that their speed is close to the speed of light.) But what does the comparable mean? Is it that the particle whose speed is more than 0.1c must take the relativistic effect into account? 2. Relevant equations 3. The attempt at a solution Thank you!