Elasticity
If an external force is applied to a material, it causes deformation in molecular structure of that material. By removing this force, material turns its original shapes; we call this process as elasticity of material. It is the ability of returning its original shape after removing the applied stress. Elasticity can be explained by the Hooke’s Law. In other words, amount of compression or stretching is directly proportional to the applied force. However, until certain point under applied force materials regain their original shapes.
This certain point is called elastic limit of that material. It is specific for each material and distinguishing property of solid matters. Look at the given pictures. You see the elasticity of the spring and rubber. Forces are applied and at time t, they are compressed by the external forces, however, after removing the forces they regain their original shape at time 2t.
We can say that forces, applied to the spring and rubber, are below the elastic limit of these materials. If they are not below these limits rubber and spring are permanently distorted. Picture given below shows the example of this situation.
