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Hooke's Law

It is the basic law in the elasticity. It states that the extension produced in a wire directly proportional to the load attached to it.

Thus, according to Hooke's law,
Extension load
However, this proportionality holds good upto certain limit called the elastic limit.

Hooke's law can be easily verified by suspending a long metallic wire of uniform area of cross-section from a rigid support and noting the extension (increase in its length) on loading it. The extension can be measured accurately within a Vernier arrangement. As load is increased in steps, it is found that the extension is always directly proportional to the load.

In 1807, English physicist Thomas Young pointed out that the load and the extension are more schematically described in terms of stress and strain respectively. Thus, Hooke's law may be stated that stress is directly proportional to strain and according to modified form of Hooke's law,
    stress strain
or stress = constant × strain
or = constant

This constant of proportionality is called modulus of elasticity or coefficient of elasticity of the material. Its value depends upon the nature of the material of the body and the manner in which the body is deformed. There are three modulii of elasticity corresponding to the three types of the strain, namely Young's modulus (Y), bulk modulus (K) and modulus of rigidity (η ). 

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