Elasticity is the tendency of solid materials to return to their original shape after being deformed. Solid objects will deform when forces are applied on them. If the material is elastic, the object will return to its initial shape and size when these forces are removed.

The physical explanations for elastic behavior is different materials. In metals, the atomic frame changes size and shape when forces are applied. When forces are removed, the frame goes back to the original lower energy state. For rubbers and other polymers, elasticity is caused by the stretching of polymer chains when forces are applied.

In engineering, the amount of elasticity of a material is determined by two types of material parameter. The first type of material parameter is called a modulus, which measures the amount of force per unit area (stress) needed to achieve a given amount of deformation. A higher modulus typically indicates that the material is harder to deform. The second type of parameter measures the elastic limit. The limit can be a stress beyond which the material no longer behaves elastic and deformation of the material will take place. If the stress is released, the material will elastically return to a permanent deformed shape instead of the original shape.

When describing the relative elasticity of two materials, both the modulus and the elastic limit have to be considered. Rubbers typically have a low modulus and tend to stretch a lot and so appear more elastic than metals in everyday experience. Of two rubber materials with the same elastic limit, the one with a lower modulus will appear to be more elastic. Hooke’s Law states the stress within an elastic solid up to the elastic limit is proportional to the strain responsible for it. Strain is described as the change in shape and size due to the applied forces. (Strain = extension/length) Stress is the internal force associated with a strain. (Stress = force/area)

We have discussed Hooke’s Law in the past in one of our labs, and calculated forces when different weights were placed on springs. Friction plays a huge part in Hooke’s Law because without friction the spring would never stop and we couldn’t make calculations. Hooke's Law = F = − k Δx. (Δx = the quality of extension, k is the constant of proportionality, and the - before the k is the spring attempting to return to its original shape)

When it comes to measuring elastic properties you can use moduli such as Young’s modulus, Shear modulus, or the Bulk modulus.

Young’s modulus describes tensile elasticity, or the tendency of an object to deform along an axis when opposing forces are applied along that axis; it is defined as the ratio of tensile stress to tensile strain. It is often referred to simply as the elastic modulus. Young’s modulus also known as the tensile modulus or elastic modulus, is a measure of the stiffness of an elastic material and is a quantity used to characterize materials. It is defined as the ratio of the stress along an axis to the strain along that axis in the range of stress in which Hooke's law holds. The Young's modulus enables the calculation of the change in the dimension of a bar made of an isotropic elastic material under tensile or compressive loads. For instance, it predicts how much a material sample extends under tension or shortens under compression. The Young's modulus directly applies to cases uniaxial stress, that is tensile or compressive stress in one direction and no stress in the other directions. Young's modulus is also used in order to predict the deflection that will occur in a statically determinate beam when a load is applied at a point in between the beam's supports. Other elastic calculations usually require the use of one additional elastic property, such as