# Linear elastic material

A rock is linearly elastic if it undergoes strain linearly proportional to the magnitude of applied stress. Or to put it another way, plots as a straight line on a stress strain curve. Furthermore, at the elastic limit, if the load is removed the specimen will still return back to original shape and form.

The uniaxial relation between stress and strain for a perfectly elastic solid is

Where `E` is the Young's modulus and is an intrinsic property of the material. The mechanical model for a perfectly elastic material is a simple spring. This equation is known as Hooke's Law and is often written in terms of force `F` and displacement `x` (as in simple harmonic motion):

where `k`, called the spring constant, is the elastic proportionality constant between applied stress and strain.