A shear force diagram shows the variation of shear force across the length. Shear force at a particular length can be found by taking a section at that point. For example, in order to find the shear force at a distance x in the cantilever beam, we cut the beam in two parts at a distance x from the end and consider the equilibrium of part (2). We could have considered part 1 as well, but then we have to find the support reactions first. Applying the vertical force balance to part (2), V₂ =P .

Since V₂ is downward on negative section, shear force is positive. Expression for shear force is independent of x. Thus, the shear force is constant. At a slight distance away from point B towards right, the shear force is suddenly zero, as there is no force there. Actually, the point B is the point of singularity, where the shear force rises from 0 to P. Same applies to point A, where a slight distance away from point A towards left, there is no force. Thus shear force is zero there. Now, we can drawn the shear force diagram.