 We will first focus on the mechanics of idealized point particles in special relativity. Regardless of the macroscopic objects they represent, we shall treat such particles, and by extension the corresponding physical objects, as un-analyzable wholes. We will then separately discuss “composite systems” or systems composed of such particles. Physicists use composite systems to approximate physical objects when they are interested in examining the “inner workings” of such objects, such as when they treat a gas as a collection of idealized particles. 