动量守恒定律是宏观世界和微观世界都遵守的共同规律 ,应用非常广泛 .动量守恒定律的适用条件是相互作用的物质系统不受外力 ,实际上真正满足不受外力的情况几乎是不存在的 .所以 ,动量守恒定律应用重在“三个”选取 .一、动量守恒条件近似性的选取根据动量守恒定律成立时的受 The law of conservation of momentum is a common law that both the macroscopic world and the microscopic world obey, and it is widely used. The law of conservation of momentum is that the interacting material system is not subject to external forces, and in fact it is virtually non-existent if it is actually satisfied with external forces. The application of the law of conservation of momentum focuses on the “three” choices. First, the selection of the conservation of momentum conservation conditions is based on the conservation of the principle of conservation of momentum.