Physics Study Guide/Periodic Motion

Hooke's law
$$k$$ is the spring constant and $$x$$ is the displacement (the force is the restoring force)

For this equation to be approximately accurate, $$x$$ needs to be below the spring's elastic limit. If $$x$$ is more than the spring's elastic limit, the spring will exhibit "plastic behaviour" meaning that it will not return to its original position.

Potential energy
potential energy stored in a compressed recoiled spring

$$T$$ is the period, $$m$$ is the mass, and $$k$$ is the spring constant.