What is the difference between a scientific theory and a model?
Can someone explain the ideas with the help of a theory in physics and a model of physics?
A theory is an explanation of a phenomenon in the world, which may or may not be directly experienced by our senses. For instance, children make the most fascinating theories about the things they experience.
A scientific theory is a system of consistently defined concepts and falsifiable propositions, which has the purpose of explaining a phenomenon in the world. The latter may or may not be directly experienced by our senses. Moreover, a theory has the purpose of making both reliable and valid prognostications regarding the behavior, future states or whatsoever of that phenomenon.
A model is a simplification of something. It's purpose is to make something graspable, by leaving out details, which are negligible for understanding this thing or working with it. A model may use theoretical concepts, that is, concepts defined within a scientific theory, but may also use everyday language. Moreover, a model can also consist in a visualization, like e simple diagram or a three-dimensional object--like the ones made by architects.
For example, as a layman, I would have a hard time trying to grasp the theory of relativity as formulated by A. Einstein. Luckily, physicists make models of their theories which are suited to convey at least part of their knowledge to layman. Or: The model of a building, for instance, won't have functioning washbasins, they are left aside in order to simplify.
A similarity between theories and models is: While a model is a simplification per definition, when building a theory it is advisable to follow the principle of parsimony of explanation. But that doesn't necessarily mean, that a theory must be simple. It rather means, that a theory is better than another one if it can do the same job in a simpler way.