What is defined as the internal resistance to an applied external force?

Stress is defined as the internal resistance that a material exhibits when an external force is applied to it. It quantifies how much force is transmitted through a unit area of the material, thereby giving an indication of how materials will react under various loading conditions. When an external force is exerted, it generates internal forces within the material, leading to deformation. The measure of this internal force relative to the area over which it is distributed is what we term as stress.

The concept of stress is pivotal in understanding how materials behave under external loads, including how they yield, deform, or ultimately fail. It is foundational in engineering and materials science, providing critical insights into material performance and safety. Thus, stress serves as a key element in evaluating the integrity and viability of structures and components when subjected to loads.