A weird reality up until now is that we have dealt with one body problems. Sure we have had things interact with that body but the focus has always been on one body moving and one body experiencing force. In this section we talk about what happens when you have two bodies collide with each other and how it impacts their motion by examining their momentum. In this video I tried talking about the idea of systems and systems analysis but it is an idea and approach to problem solving that becomes much more applicable if we were to move onto energy.