English: Illustration of isotropic normal tensile stress. Top left: Each face of a cube of homogeneous material is under traction by a force withmagnitude F, applied evenly over the entire face. Top right: the force applied by the material across an imaginary section S parallel to one of the faces is also F, so the stress is normal and equal to F/A, where A is the area of S (and of the face). Bottom left: if S is a diagonal cut parallel to one edge, the force across S will have to balance the two forces shown. The magnitude of that force is F*sqrt(2), but the area is also A*sqrt(2), so the stress is again perpendicular to S and equal to F/A. Top right: if S is a cut across three corners of the cube, as shown, the force across S would have to balance the three forces shown, each equat to F/2. The magnitude of the force across S is Fsqrt(3)/2, but the area of S is A*sqrt(3)/2, so the stress is again normal to S and equal to F/A. Drawn by J.Stolfi with Inkscape, according to the style of File:Axial_stress.svg.