ABSTRACT
Modeling is the art of describing in symbolic language a real life system so that approximately correct predictions can be made regarding the behavior or evolution of the system under varied circumstances of interest. The important aspect of the definition is that a model should be "solvable". One should also bear in mind that every model is constructed with certain limitations on its validity, and these should be borne in mind by the prospective user. As to the problems which require model construction, their source and scope vary between applied problems in life to attempts to duplicate natural phenomena and intellectual curiosity. Though it is accepted and proven that Einstein's theory is better and more accurate, still it is highly complex and "hard to solve". As a result, in most terrestrial applications we use Newton's Law of Gravitation with "acceptable error margin".
