In the above discussion, it is implicitly assumed that the bending moment is positive when the top of the beam is compressed. That can be 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 − σ 0 {\displaystyle -\sigma _{0}} and let the bottom of the beam have a stress σ 0 {\displaystyle \sigma _{0}} .