X. i5ng> learning goal: understand that, for many purposes, a system can be treated as a point-like particle with its mass concentrated at the center of mass.
a complex system of objects, both point-like and extended ones, can often be treated as a point particle, located at the system's center of mass. such an approach can greatly simplify problem solving.
before you use the center of mass approach, you should first understand the following terms:

system: any collection of objects that are of interest to you in a particular situation. in many problems, you have a certain freedom in choosing your system. making a wise choice for the system is often the first step in solving the problem efficiently.