In biomechanics, which statement best defines stress?

In biomechanics, which statement best defines stress?

• A. It is the tissue's internal response to an applied external load
• B. It is the external force applied to tissue
• C. It is the rate of tissue deformation
• D. It is the material's stiffness

Answer: (A)

Stress is the tissue’s internal response to an externally applied load, meaning it is the internal force per unit area that develops to resist the external force. This distinction matters because the same external load can produce different stress levels depending on how it’s distributed over a area within the tissue. Stress can be normal (perpendicular to a surface) or shear (parallel to a surface), reflecting how internal forces balance the applied load. This concept differs from the external load itself, which is simply the force applied to the tissue, and from deformation-related ideas like strain or strain rate, which describe how much or how fast the tissue deforms under that stress. It also differs from stiffness, which is a property of the material describing its resistance to deformation, not the internal stress state itself.

Stress is the tissue’s internal response to an externally applied load, meaning it is the internal force per unit area that develops to resist the external force. This distinction matters because the same external load can produce different stress levels depending on how it’s distributed over a area within the tissue. Stress can be normal (perpendicular to a surface) or shear (parallel to a surface), reflecting how internal forces balance the applied load.

This concept differs from the external load itself, which is simply the force applied to the tissue, and from deformation-related ideas like strain or strain rate, which describe how much or how fast the tissue deforms under that stress. It also differs from stiffness, which is a property of the material describing its resistance to deformation, not the internal stress state itself.