Hooke’s Law:
Fs = −kx
where F is force, k is spring constant, and x is spring extension.
the force required to extend a spring is directly proportional to the amount of extension.
This is equally true for spring compression.
The negative for k exists because the k factor is fighting against the force extending the spring: k is the restoring force of the spring.
A limit of proportionality exists:
the maximum stress or force the spring can withstand without undergoing permanent deformation.