A model that takes on the physical appearance of the object it is to portray is called a physical model. This type of model is used to display or test the design of items ranging from new buildings to new products. In the aircraft industry scale models of new aircraft are built and tested in wind tunnels to record the aerodynamics of design. An automobile-parts manufacturer may have a three-dimensional scale model of the plant floor, complete with miniature machines and equipment, so that a new layout of the plant can be analysed. The machines in the model can be rearranged and new layouts studied in order to improve the material flow.
Mechanical models have the advantage of being usable for experimentation. In the aircraft example, the testing of a different design may mean that a completely new model must be built. In addition to offering the advantage of experimentation, mechanical models lucidly describe the problem or system under study; this is helpful in generating innovative design alternatives for solving the decision problem. Nevertheless, only a relatively small class of problems can be solved with mechanical models. Problems such as portfolio selection, media selection, and production scheduling are examples of problems that cannot be analysed with a mechanical model.
;Basically, mechanical models are useful only in design problems and even some of these can be analysed more efficiently and completely with mathematical models which can be computerised. Besides this, mechanical models do not contain explicit relationships between the decision alternatives and dependent variables or objectives and dependent variables or objectives and, trial-and-error methods of problem solving must be used. Although this in itself is not a major drawback, the trial-and-error process, coupled with a need to rebuild the model for each design change, can lead to a very time-consuming and costly process in some cases.