Elasticity is the property of a material to regain its original shape after deformation when the external forces are removed.

Explanation:
When a material is subjected to external forces, it undergoes deformation. This deformation can either be elastic or plastic. Elastic deformation is temporary and reversible, while plastic deformation is permanent and irreversible.

Elasticity is the ability of a material to return to its original shape and size after the applied forces causing the deformation are removed. This property is essential in many engineering applications, as it ensures that the material can withstand repeated loading and unloading cycles without permanent deformation.

Key Points:
- Elastic deformation: When a material is subjected to external forces, it may undergo elastic deformation. In this case, the material is able to stretch or compress and still return to its original shape and size once the forces are removed.
- Temporary and reversible: Elastic deformation is temporary because it only occurs while the external forces are applied. Once these forces are removed, the material regains its original shape and size. This means that the deformation is reversible, and the material does not retain any permanent deformation.
- Importance in engineering applications: Elasticity is a desirable property in many engineering materials because it allows them to withstand repeated loading and unloading cycles without undergoing permanent deformation. This is particularly important in structures and components that experience dynamic or cyclic loading, such as bridges, buildings, and mechanical parts.
- Stress-strain relationship: The elastic behavior of a material is described by its stress-strain relationship. The stress is the applied force per unit area, while the strain is the resulting deformation. In the elastic range, the stress-strain relationship is linear, and the material follows Hooke's law, which states that stress is directly proportional to strain.
- Elastic modulus: The elastic modulus is a measure of a material's stiffness or resistance to deformation. It is defined as the ratio of stress to strain in the elastic range. The three most common types of elastic modulus are Young's modulus, shear modulus, and bulk modulus.
- Limitations of elasticity: While elasticity allows a material to regain its original shape after deformation, it has its limitations. If the applied forces exceed the material's elastic limit, it will undergo plastic deformation and retain permanent deformation even after the forces are removed. The elastic limit is the maximum stress or strain that a material can withstand without permanent deformation.