What is defined as the ratio of tensile stress to tensile strain?

Young's modulus is a fundamental property of materials that quantifies their stiffness. It is defined as the ratio of tensile stress (the force applied per unit area) to tensile strain (the deformation or elongation experienced by the material). This relationship is linear and applies to the elastic region of the material's stress-strain curve, which means that as stress is applied, the material will deform proportionally to the stress, as long as the elastic limit is not exceeded.

In practical terms, Young's modulus provides insight into how much a material will stretch or compress under a given load. A higher Young's modulus indicates a stiffer material that deforms less under the same amount of stress, while a lower value suggests a more flexible material.

Other options refer to different properties of materials. The shear modulus measures how a material deforms under shear stress, while the bulk modulus relates to a material's ability to compress under uniform pressure. The elastic limit is the maximum stress that a material can withstand without permanent deformation but does not directly define a ratio involving stress and strain. Therefore, Young's modulus is the appropriate choice for this definition.