Total Mechanical Energy (TME) – the sum of the kinetic and the potential energies ET Ek Eg Ee As an object moves, one of the following results must occur. • The system’s total mechanical energy is conserved only if there is no friction to dissipate any energy and there are no external forces so no work is done. (In other words the system is frictionless and isolated). • The total mechanical energy of the system changes when some of the mechanical energy is dissipated (and is then stored as thermal energy, light energy, etc.). • The system’s total mechanical energy changes due to energy being transferred into or out of the system by means of an external force (by a process we call work).