Within the elastic limit, according to Hooke's Law, stress is proportional to strain. The constant of proportionality for longitudinal stress and strain is called Young's Modulus ($Y$): $Y=\frac{\text{Longitudinal Stress}}{\text{Longitudinal Strain}}=\frac{F/A}{\Delta L/L}=\frac{FL}{A\Delta L}$

• It is a characteristic property of the material and does not depend on the dimensions of the object.
• It indicates the stiffness of the material: higher $Y$ means the material is harder to stretch.