Something that is elastic can be stretched or deformed (changed) and returned to its original form, like a rubber band. It tries to come back to its first shape. The stress is the force applied; the strain is how much the shape is changed, and the elastic modulus is the ratio between those numbers.
The simplest model for elasticity is Hooke's law. It says that the force to stretch something (F) is proportional to the distance it is stretched (x). This is usually written as , where is a constant called the spring constant. If it is easy to stretch a material, that material has a lower k value.
Elastic materials are different than plastic materials. A plastic material can be stretched or deformed, but it will not return to its original form.
