Bending Moment explained very well in this video demonstration. A Bending Moment is a subsitute for a force. Watch this video demonstration.
A bending moment is the reaction induced in a structural element when an external force or moment is applied to the element causing the element to bend. The most common or simplest structural element subjected to bending moments is the beam. The example shows a beam which is simply supported at both ends.
Conical Concrete Pour Demonstration by Lura Enterprises