The measure of a material's resistance to deflection under load is called what?

• A. Ductility
• B. Toughness
• C. Hardness
• D. Stiffness

Answer: (D)

Stiffness describes how much a material resists bending or deflecting when a load is applied. If a material is stiff, it deflects only slightly under a given force; a less stiff material will bend or sag more. Put simply, deflection is inversely related to stiffness: under a fixed load, a higher stiffness means a smaller movement. In bending, stiffness combines the material’s modulus of elasticity with the cross‑section’s geometry, so stiffer materials (and thicker sections) resist deflection more effectively. Other properties describe different behaviours: ductility is how much plastic deformation you can get before failure, toughness is how much energy a material can absorb before breaking, and hardness is how resistant the surface is to indentation. None of those directly measure resistance to deflection under load, which is what stiffness captures.