Which property is defined as the elastic modulus divided by density?

• A. Specific tensile modulus
• B. Specific tensile stress
• C. Hardness
• D. Toughness

Answer: (A)

The property being tested is stiffness per unit weight. Dividing the elastic modulus by density yields the specific modulus, also called the specific tensile modulus, which measures how stiff a material is for a given mass. This is particularly important in lightweight design, where you want high stiffness without adding much weight. The units come out to roughly J/kg, reflecting energy per unit mass associated with elastic deformation and providing a direct way to compare materials for weight-constrained applications.

Hardness and toughness describe different aspects: hardness relates to resistance to indentation, and toughness is the total energy needed to fracture a material; neither is simply the elastic response per unit mass. A ratio like σ/ρ would be a form of specific strength, not the specific modulus.