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 e¤ects 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.