Shear forces and bending moments are resultants which are used to conveniently represent the internal forces that develop within a beam when external loads are acting on it.

Let’s examine some classic examples of beam diagrams and how they react in shear and bending.

Any structural engineer will recognize this diagram as a shear and bending moment diagram for a simply supported beam with a point load at midspan. The bottom, triangular graph is the bending moment.

When a 'beam' experiences a bending moment it will change its shape and internal stresses (forces) will be developed. The photograph illustrates the shape change of elements of a beam in bending. Note ...

M. R. Horne, The Plastic Theory of Bending of Mild Steel Beams with Particular Reference to the Effect of Shear Forces, Proceedings of the Royal Society of London.