A simple problem: a mass of 8 kg is placed on the end of a copper wire. The wire extends a distance of 4.2 cm. Calculate the potential energy stored in the wire and the loss of potential energy of the mass. The elastic strain energy stored in the wire = 1/2 . F . x = 1.65 J The loss of gravitational potential energy by the mass = mgh = 3.3 J So where has the other 1.65 J gone? In stretching, the entire wire (with the exception, presumably, of an infinitely thin cross section immediately adjoining the support) descends by varying amounts and itself loses g.p.e.. How is energy conserved? I can only conclude that the wire in descending, gains kinetic energy which is then dissipated as thermal energy. Comments please on this please especially on mechanisms involved.