momentum theorem is one of the universal theorems of dynamics. the content is that the increment of the momentum of an object is equal to the impulse of the combined external force it experiences, that is, ft = δvm, or the vector sum of the impulses of all external forces. if a system is not subject to external forces or the vector sum of the external forces is zero, then the total momentum of the system remains unchanged. this conclusion is called the law of conservation of momentum. the law of conservation of momentum is one of the most important and universal conservation laws in nature. it applies to both macroscopic objects and microscopic particles; it applies to both low-speed moving objects and high-speed moving objects. it is an experimental law and also it can be derived from newton's second law and the kinetic energy theorem.

momentum: δm＝f*δt

f = force

δt = time change