This axiom is equivalent to the symmetry of the Cauchy stress tensor. For the resultants of the stresses do not exert a torque on the volume element, the resultant force must lead through the center of the volume element. The line of action of the inertia forces and the normal stress resultants σ xx ·dy and σ yy ·dx lead through the center of the volume element. In order that the shear stress resultants τ xy ·dy and τ yx ·dx lead through the center of the volume element