Modeling and simulating collections of physical objects which are subject to a wide variety of physical forces and interactions is exceedingly difficult. The construction of a single simulator capable of dealing with all possible physical processes is completely impractical and, it seems to us, wrong-headed. Instead, we propose to build custom simulators for single, particular collections of physical objects and where pre-specified physical phenomena are involved. For such an approach to be practical, an environment needs to be provided that facilitates the quick construction of these simulators. In this paper we describe the essential features of such an environment and describe in some detail how a general implementation of the weight residual method, one of the more general classes of numerical integration techniques, can be used.