The three fundamental areas of engineering mechanics are statics, dynamics, and mechanics of materials. Statics and dynamics are devoted primarily to the study of the external effects upon rigid bodies—that is, bodies for which the change in shape (deformation) can be neglected. In contrast, mechanics of materials deals with the internal e¤ects and deformations that are caused by the applied loads. Both considerations are of paramount importance in design. A machine part or structure must be strong enough to carry the applied load without breaking and, at the same time, the deformations must not be excessive.