ABSTRACT
A "particle" is considered to be a small physical entity which may be represented (or "modeled") by a point with an associated mass. "Small" is, of course, a relative term. Many objects such as projectiles, automobiles, space vehicles, and even heavenly bodies are commonly regarded as being particles even though they are hardly small or minute. Hence, for such representations to produce useful results, the object, be it a ball, a car, an airplane, or even a planet, must be small relative to its surroundings. In any event the modeling of an object as a particle, and then as a point with an associated mass, becomes increasingly accurate the smaller the object is.
