What is shear force and bending moment

Shear force is a force acting perpendicular to the axis of a structural member. It tends to cause one part of the member to slide relative to an adjacent part. Imagine cutting a deck of cards with a knife; the knife applies a shear force. In a beam, shear forces are typically largest near the supports.

A bending moment is a measure of the bending effect on a structural member. It's caused by forces that create a tendency for the member to bend or rotate. For example, if you place a load in the middle of a plank supported at both ends, the plank will bend, and there will be a bending moment within it. The bending moment is often greatest at the center of the span for a simply supported beam with a central load.