Concepts and rules of the game

Abstract

Taking a commonsense view, the world we live in is composed of quantities of matter which influence each other physically in a variety of ways, depending on the nature of the matter, on whether the lumps are in relative motion and on the nature of their motion. Matter is_xpresented to us in three partly, interchangeable forms: We describe as solids, materials which are hard and heavy and capable of retaining their shape. Many solids turn out to have a highly ordered or crystalline atomic structure. Experience teaches us to classify as fluids those materials which readily flow and which, speaking generally, are light or very light in com­parison with solids. Amongst fluids we can readily distinguish between those capable of being poured into a vessel, where they fit themselves to its shape and form a horizontal free surface, and those which invariably expand to fill the container provided. The first kind of fluid we call liquids. These possess a disordered atomic or molecular structure overall, but extremely locally, and for very brief periods, a crystalline structure can be present. Gases, the other and lighter kind of fluid, lack any orderly atomic or molecular structure.