Which term is defined as the force per unit area that expresses internal force intensity?

• A. Strain
• B. Stress
• C. Toughness
• D. Elasticity

Answer: (B)

Stress is the internal distribution of force within a material that resists external loads, defined as force per unit area (sigma = F/A). It expresses how intensely the material is loaded from within. Units are typically Pascals (N/m^2). This is different from strain, which describes how much the material deforms relative to its original size (change in length divided by original length). Toughness is the amount of energy the material can absorb before fracturing, and elasticity refers to how readily a material returns to its original shape after removing the load. For a beam or rod under load, the internal force per area that tells you how intensely the material is being stressed is stress. For example, doubling the applied force or halving the cross-sectional area increases stress, while a larger area reduces it.