Law of conservation of mechanical energy K:+u =ke+u In a system in which only conservative forces do work the total mechanical energy remains constant In this chapter: we consider systems of particles for which the energy can be changed by the work done by external forces(系统外的力) and nonconservative forces Ch 13 Energy III: Conservation of energyCh.13 Energy III: Conservation of energy In this chapter: we consider systems of particles for which the energy can be changed by the work done by external forces(系统外的力) and nonconservative forces. Ki +Ui = K f +U f Law of conservation of mechanical energy: “In a system in which only conservative forces do work, the total mechanical energy remains constant