The effective equation of state for a string with short-wavelength perturbations is shown to be $\ensuremath{\mu}T={\ensuremath{\mu}}_{0}^{2}$, where $\ensuremath{\mu}$ and $T$ are the mass density and tension in the rest frame of the string and ${\ensuremath{\mu}}_{0}$ is the unperturbed string tension. The dynamics of "wiggly" strings in flat spacetime is discussed. The conclusions are in agreement with the results obtained by Carter using different methods.