On the concept of model in physics

The concept of model is the basis for theoretical and experimental research in physics. A model is defined as an application of physical theories to the description of a physical system. As a premise to the introduction of models, physical theories are defined as mathematical frameworks with a hypothetical-deductive structure, provided with a mapping on the real world, allowing the description of a class of phenomena. The main characteristics of theories are discussed, in particular the domain of application and the relationships between different theories. The concept of physical system is introduced as a subset of the universe that is defined thanks to the property of separability and is characterized by appropriate boundary conditions. The structure and the main characteristics of models are then discussed and the steps to be taken to construct a model are considered. The role of assumptions is underlined and different kinds of models are illustrated. Finally, four examples of simple physical models are described, that are fit to be used for didactic purpose.