I have a thought experiment for physicists and thermodynamicists and the like. Those who are always looking for 2+2=4 but for some reason avoid discussing certain issues that are very clear. Simply put the picture where we have an object of mass m in the ground. The physics math show that we have zero gravitational potential energy there. We need to do work in order to gain potential energy. This work is meant to have a negative sign. Then when the object falls, it does a positive work because kinetic energy, and then we have the plus work minus negative work equal zero..... Ok, enough talk. Now look into reality.... If the object breaks at the time it reach ground, where do we add that energy, the internal energy (energy of deformation?), in the 'perfect' thermodynamic cycle?? And what if instead of the object being a simple rock, it is some mechanism composed of magnet, solenoid, and a spring..... Obviously when such a mechanism hit ground after falling, it presents an electric current for the very basic reason of mechanical vibration and electromagnetic induction.