Which property of springs allows them to return to original shape after being stretched?

The property of springs that allows them to return to their original shape after being stretched is elasticity. Elasticity refers to the ability of an object to deform under stress (such as stretching or compression) and then return to its original shape once the stress is removed. This behavior is typical of elastic materials, which include most springs.

When a spring is stretched, the forces within the material cause it to elongate. Once the stretching force is no longer applied, the internal forces within the spring work to restore it to its original, unstressed position. This capacity to recover from deformation is crucial in applications like mechanical systems where springs are often used to provide forces, absorb shock, or store energy.

Plasticity, on the other hand, refers to the ability of a material to undergo permanent deformation when a force is applied. Density relates to how much mass is contained in a given volume and does not affect the ability of a spring to return to its original shape. Viscosity describes the resistance of a fluid to flow, which is irrelevant for solid springs. Thus, elasticity is the correct and relevant property that explains why springs can return to their initial shape after being deformed.