Zero-rest-length spring
= Zero-rest-length spring
{title2=$V=\kappa s^2/2$}
A <zero-rest-length spring> has quadratic <potential energy> in its actual length $s$, with no subtracted natural length. It is a useful idealization, not an ordinary unstretched <spring> of arbitrary length. For an end-to-end <spring> on a two-link pendulum, changing the natural length changes the quadratic bending stiffness about the straight configuration.