Bar, a deformable solid whose transverse dimensions are noticeably smaller than its longitudinal one. The line through the centroids of the cross sections is called the axis of the bar. If the axis of the bar is straight, the bar is called a straight bar. A straight bar of constant cross section is also called a rod. A bar is often met with as an element of a structure, a building or a machine, and special methods have therefore been developed for calculating the stresses and strains in a bar. (for example, bending, torsion).