The strength of materials is a topic important for the study of solids in many applications. It describes the mechanical behaviors of materials in response to forces that act on objects (such as stress, deformation, strain and stress-strain relations). Usually, the strength of a material is described with units of pressure, because then the value can be applied to many different shapes. For example, a wire and a rod made out of the same steel may have the same tensile strength but the thicker rod will require more force to break.