13-1 Work done on a system by external forces △K+△U= (13-1) SyS SyS ext Positive external work done by the environment on the system carries energy into the system, thereby increasing its total energy i vice versa The external work represents a transfer of energy between the system and the environment. Ch 13 Energy III: Conservation of energyCh.13 Energy III: Conservation of energy 13-1 Work done on a system by external forces Positive external work done by the environment on the system carries energy into the system, thereby increasing its total energy; vice versa. The external work represents a transfer of energy between the system and the environment. Ksys + Usys =Wext (13-1)