What is the ratio of stress to strain called?

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

Answer: (C)

The main concept here is how stiffness is quantified in a material. The ratio of the internal resistance to deformation (stress) to the resulting deformation (strain) defines the modulus. In the elastic, linear region, stress and strain are proportional, and their ratio is the modulus of elasticity—often called simply the modulus. This tells you how stiff a material is: a high modulus means you need a lot of stress to achieve a small strain (steel), while a low modulus means the material deforms more easily (rubber). There are specific moduli for different kinds of deformation, like Young’s modulus for axial loading, but the general idea is the same: modulus is the stress-to-strain ratio.