What is the internal resistance to an externally applied force called?

• A. Stress
• B. Strain
• C. Pressure
• D. Tension

Answer: (A)

Internal resistance to an externally applied force is called stress. When a load acts on a material, internal forces develop to oppose that load, distributed over the cross-sectional area. That internal force per unit area is stress, measured in pascals (newtons per square meter). For a simple pull, the tensile stress inside a rod is given by stress = force divided by area, F/A. If the material stretches, the amount of deformation is called strain, which is the change in length relative to the original length. Stress and strain are related for many materials (elastic behavior) by properties like Young’s modulus.

It helps to separate the ideas: stress is the internal resistance to the load, strain is the resulting deformation, and pressure is a related concept used for fluids or for forces applied perpendicular to surfaces in all directions. Tension is a type of stress caused by pulling, but the general term describing the internal resistance to an applied force is stress.