following physically meaningful names:
P: The component of the resultant force that is perpendicular to the cross section, tending to elongate or shorten the bar, is called the normal force. V: The component of the resultant force lying in the plane of the cross section, tending to shear (slide) one segment of the bar relative to the other segment, is called the shear force. T: The component of the resultant couple that tends to twist (rotate) the bar is called the twisting moment or torque. M: The component of the resultant couple that tends to bend the bar is called the bending moment.
The deformations produced by these internal forces and internal couples are shown in Fig. 1.4.