• $word_{count}$: 200

Elasticity is the property of materials to regain their original shape and size after the removal of deforming forces. When an external force acts on a body, it develops internal restoring forces that oppose the deformation. If the body fully recovers upon force removal, it is elastic; if it retains permanent deformation, it is plastic. No material is perfectly elastic or plastic — quartz comes closest to perfect elasticity, while putty approaches perfect plasticity.

At the atomic level, elasticity arises from intermolecular forces. When atoms are displaced from equilibrium positions, restoring forces (attractive when stretched, repulsive when compressed) pull them back. This works within a limited range — the elastic limit. Beyond this, atomic bonds rearrange permanently (plastic deformation). The elastic limit depends on the material, temperature, and rate of loading.

For JEE, the key concept is that elasticity is measured by elastic moduli $\frac{stress}{strain}$, not by how much a material can stretch. Steel is more "elastic" than rubber because it has a higher modulus — it resists deformation more strongly. Rubber is more "stretchable" but less "elastic" in the physics sense.