What does the modulus of elasticity measure?

The modulus of elasticity is a fundamental property of materials that quantifies their stiffness. It is defined as the ratio of stress to strain within the proportional limit of the material. Stress is the force applied per unit area, while strain is the amount of deformation experienced by the material in response to that stress. A higher modulus of elasticity indicates a stiffer material, which means it deforms less under applied stress. This concept is crucial in engineering and material science as it helps in predicting how materials will behave when subjected to forces, ensuring structural integrity and design effectiveness.

In contrast, the other options relate to different material properties. The ability to conduct electricity pertains to electrical conductivity, which is not linked to the modulus of elasticity. The density of a material relates to its mass per unit volume and does not account for material deformation under forces. Lastly, thermal expansion describes how materials expand when heated, which is a different property entirely and unrelated to stiffness. Understanding the modulus of elasticity is essential for selecting appropriate materials for engineering applications, as it directly influences performance under load.