LAW:It States that under direct loading, within proportionality limit, stress is directly proportional to strain.i.e stress ∝ strainσ = E∈where, E is a constant of proportionality and known as YOUNG’s Modulus of elasticity. 1. Hooke’s law is valid up to the limit of proportionality. However, for mild steel proportionally limit and elastic limit are almost equal. But for other metals, the elastic limit may be higher than the proportionality limit. E.g Rubber.2. The slope of the stress-strain CURVE is called the modulus of elasticity (E). The modulus of elasticity (E) is the constant of proportionality which is defined as the intensity of stress that causes unit strain. THUS, the modulus of elasticity (E) has the unit the same as that of stress.