The internal resistance to an external force applied to a body is known as:

The internal resistance to an external force applied to a body is referred to as stress. Stress is defined as the force applied per unit area within materials and is a measure of the internal forces that develop in response to external loading.

When an external force acts on a material, it induces internal forces that resist the deformation caused by that force. This resistance is quantified as stress, which has units of force per area, such as Pascals (Pa) or pounds per square inch (psi). Stress is an essential concept in mechanics and material science, as it helps evaluate how materials respond to different types of loads, including tension, compression, and shear.

Other related terms like strain, Young's Modulus, and ultimate strength have distinct definitions and applications. Strain refers to the deformation per unit length experienced by the material. Young's Modulus is a measure of the stiffness of a material, relating stress to strain, while ultimate strength is the maximum stress that a material can withstand before failing. Understanding stress is fundamental in the analysis of structural integrity and material behavior under load.