What is the force called that causes a structure to sag when placed in the middle of it?

The force that causes a structure to sag when a load is applied in the middle is referred to as bending. Bending occurs when an external load is applied to a structural element, resulting in a combination of compressive and tensile forces within the material. Specifically, the material experiences compression on the side where the load is applied and tension on the opposite side.

When a load is concentrated at the center, the material bends downward due to the moment caused by the load. This bending moment is responsible for the curvature that leads to sagging. The analysis of bending is crucial in structural engineering, as it allows engineers to predict how beams and other structural elements will perform under load, ensuring safety and functionality.

In this context, the other terms refer to different types of forces: compression involves pushing forces that shorten a material, tension involves pulling forces that elongate a material, and shear refers to forces that cause sliding between parts of a material. Each of these forces plays a role in structural behavior, but bending specifically describes the phenomenon of sagging under a centrally applied load.