Explain the difference between stress and strain.

Explain the difference between stress and strain.

• A. Stress is the internal force per unit area; strain is deformation per unit length.
• B. Stress is the rate of deformation; strain is the rate of force.
• C. Stress is the energy stored per unit volume; strain is deformation per unit length.
• D. Stress is the external force; strain is the total deformation.

Answer: (C)

The main idea is to separate how the material responds to loads from how much it actually changes shape or length. Stress is the internal resistance generated inside a material when a load is applied, defined as the force per unit area (sigma = F/A). It tells you how much the material tries to push back against the load. Strain, on the other hand, is the measure of deformation, defined as the change in length divided by the original length (epsilon = delta L / L0). It’s a dimensionless quantity that tells you how much the material has stretched or compressed. For context, energy stored per unit volume describes strain energy density, which is related to both stress and strain through w = 1/2 sigma epsilon in linear elasticity, but that is about energy, not the definitions of stress or strain themselves. The option that describes stress as energy per unit volume confuses these concepts, and the option that describes stress as a rate of deformation or as external force conflates different physical ideas. The correct distinction is internal force per area versus relative deformation.

The main idea is to separate how the material responds to loads from how much it actually changes shape or length. Stress is the internal resistance generated inside a material when a load is applied, defined as the force per unit area (sigma = F/A). It tells you how much the material tries to push back against the load. Strain, on the other hand, is the measure of deformation, defined as the change in length divided by the original length (epsilon = delta L / L0). It’s a dimensionless quantity that tells you how much the material has stretched or compressed.

For context, energy stored per unit volume describes strain energy density, which is related to both stress and strain through w = 1/2 sigma epsilon in linear elasticity, but that is about energy, not the definitions of stress or strain themselves. The option that describes stress as energy per unit volume confuses these concepts, and the option that describes stress as a rate of deformation or as external force conflates different physical ideas. The correct distinction is internal force per area versus relative deformation.