Tensile forces cause materials to extend and compressive forces cause negative extension.Hooke's Law states that the force needed to extend a spring is directly proportional to the extension of the spring provided the limit of proportionality is not reached.Up to the elastic limit, elastic deformation occurs.Beyond the elastic limit, the spring does not return to its original length when the force is removed and plastic deformation occurs.The elastic limit is the maximum extension or compression that a material can undergo and still return to its original dimensions when the force is removed.
ΔF = k Δx
ΔF = k Δx