It is emphasized that a distribution function in both the dislocation loop lengths and obstacle strengths must be considered to develop a quantitative theory for the hysteretic dissipation of energy. That is when dislocation surmounts and undulating internal stress field and the break-away is restricted by a restoring force considered to be that of dislocation line tension. The significance of the average friction stress resisting dislocation motion being related to the dislocation structure and impurity effects in copper is demonstrated. The amplitude dependent internal friction in copper is demonstrated. The amplitude dependent internal friction in copper in the decrement range of 3 x 10-2 to 2 x 10-1 is shown to be hysteretic in nature and can be analyzed by the Kressel-Brown and Roberts theories yielding realistic dislocation structural parameters.