The conditions of the law of conservation of momentum are mainly as follows:
There are no external forces acting on the system, or the sum of the external forces on the system is zero. This is because external forces change the momentum of the system, and the law of conservation of momentum requires that the total momentum of the system remain constant. If the system is acted upon by an external force, then the momentum is no longer conserved. In fact, there is no such thing as an object being subjected to an external force, and when applying the law of conservation of momentum, it is mainly considered that the external force on the system is much less than the interaction force between the objects, or the system is not affected by an external force in a particular direction or the external force is much less than the internal force, so that the influence of the external force can be ignored.
The interaction forces inside the system must meet certain conditions, including that the interaction forces should be in the same direction, equal in magnitude, and in the same time. Only if these conditions are met, the total momentum of the system can remain constant.
The quality of the system is to remain the same. This is because mass is a measure of momentum, and if there is a change in the mass of the system, then the total momentum of the system will also change. Therefore, for momentum to be conserved, the total mass of the system must remain constant.
The shape and size of the system should remain the same. This is because changes in shape and size affect the momentum distribution of the system and thus the total momentum of the system. Therefore, for momentum to be conserved, the shape and size of the system must remain the same.
The initial and final state of the system is known. This is because the law of conservation of momentum is verified by comparing the initial and final states of the system. If the initial and final states of the system are unknown, then there is no way to verify whether the momentum is conserved or not.
When judging whether momentum is conserved or not, it is first necessary to clarify the type of system and the motion state of the object, and then choose an appropriate judgment method to analyze the problem. For example, in mechanical engineering, Newton's laws can be used to analyze the state of motion of a system and to determine whether momentum is conserved or not. In a chemical reaction, it is possible to judge whether momentum is conserved or not based on the breaking and formation of chemical bonds.
The above information is for reference only, it is recommended to consult a physics professional or consult the literature related to the law of conservation of momentum for more comprehensive and accurate information.