seen if we consider a linear distribution of stress in the beam and find the resulting bending moment. Let the top of the beam be in compression with a stress and let the bottom of the beam have a stress . Then the stress distribution in the beam is . The bending moment due to these stresses is where is the area moment of inertia of the cross-section of the beam. Therefore, the bending moment is positive when the top of the beam is in compression. Many authors follow a different convention in which the stress resultant is defined as In that case, positive bending moments imply that the top of the beam is in tension. Of course, the definition of top depends on the coordinate system being used. In the examples above, the top is the location with the largest -coordinate. See also Buckling Deflection including deflection of a beam Twisting moment Shear and moment diagrams Stress resultants First moment of area Influence line Second moment of area List of area moments of inertia Wing bending relief References External links Stress resultants for beams Free online Calculation tools for bending moment Force Continuum mechanics Civil engineering Moment (physics) ja:断面力#曲げモーメント