求翻译：机械能守恒定律是动力学中的基本定律，即任何物体系统如无外力做功或外力做功之和为零，系统内又只有保守力做功时，则系统的机械能保持不变。是什么意思？

Conservation of mechanical energy is the basic laws of dynamics, that is, any object systems such as external forces acting or external forces acting zero, the system only conservative forces do work, then the mechanical energy of the system remain unchanged.

Mechanical energy is 守恒定律 dynamics in the Basic Law, that is, any object system such as No external force or forces 做功 做功 for zero, the system is only conservative force 做功, the system of mechanical energy is unchanged.

The mechanical energy conservation relations are in the dynamics fundamental law, namely sum of any object system like non-external force acting or the external force acting is the zero, in the system when the conservative force acting, then the system mechanical energy maintenance is invariable.

Mechanical energy conservation law is the fundamental law of dynamics, that any work of object system if there is no external force or outside forces sum to zero, when only conservative force doing work within the system, the mechanical energy of the system remains unchanged.

正在翻译，请等待...