除了重力和系统内弹力做功,其它力做功的代数和为零时,系统机械能守恒,常见的表述有以下几种:(1)E1=E2,系统初状态的总机械能等于末状态的总机械能;(2)ΔEk=-ΔEp,系统动能的变化量与势能的变化量大小相等,符号相反.在具体解题中通常表述为系统动能的增加量等于势能的减少量,即 In addition to gravity and system elastic work, the mechanical energy of the system is conserved when the algebraic sum of other force work is zero. Common expressions are as follows: (1) E1 = E2, the total mechanical energy in the initial state of the system is equal to the total mechanical energy in the end state; (2) ΔEk=-ΔEp, the amount of change in kinetic energy of the system is equal to the change in potential energy, and the sign is reversed. In the specific problem, it is usually stated that the increase of system kinetic energy is equal to the reduction of potential energy, ie