Mechanics of materials is one of the sciences underlying the design of any device that must support loads, from the simplest machines and tools to complex vehicles and structures. Three fundamental questions are examined. Will an object or structure support the loads acting on it? Answering this question requires introducing the state of stress, which describes the forces within a material. The state of stress must be determined at each point of a structure to ensure that it does not exceed the capacities of the materials used. What is the change in shape, or deformation, of an object subjected to loads? Design engineers must be concerned with how objects change shape due to the loads acting on them.