Shearing force and bending moment diagrams

When a beam carries loads, it experiences internal forces and moments that cause it to bend. Shearing force is the internal force acting perpendicular to the beam, while bending moment is the turning effect that causes the beam to curve. Think of a wooden plank supported at both ends with weights placed on it—the plank wants to break near the supports, and these diagrams show exactly where and how much.

For simple supported beams like a footbridge across a stream, you draw two diagrams: one showing how shearing force changes along the beam's length, and another showing bending moment distribution. Cantilever beams, like a balcony jutting from a building, have maximum moment at the fixed end.

With concentrated loads (point loads), diagrams show sharp changes, while uniformly distributed loads create sloped and curved lines respectively.