original_query: How does referring the motion of constituent particles to their center of mass allow a subsystem to be decoupled from the larger system it is embedded in? What is the most relevant chunk to answer the query?
query: How does referring the motion of constituent particles to their center of mass allow a subsystem to be decoupled from the larger system it is embedded in?
answer: In Newtonian mechanics, a subsystem can be decoupled from a larger system by referring the motion of its constituent particles to their center of mass. This is because the influence of the larger system is irrelevant for the internal dynamics of the subsystem;  the object's acceleration is the vector sum of accelerations due to individual forces.