Hooke’s law states that for relatively small deformations of an object, the displacement or size of the deformation is directly proportional to the deforming force or load. Under these conditions, the object returns to its original shape and size upon the removal of the load. Elastic behaviour of solids according to Hooke’s law can be explained by the fact that small displacements of their constituent molecules, atoms or ions from normal positions are also proportional to the force that causes the displacement. It is valid only in the proportional region of the stress–strain curve.