Okay, so I'm at conundrum with my physics text book and I cannot seem to understand a few concepts. Allow me to elaborate. 1. Why is the total momentum of a firecracker sliding on ice the same before and after it explodes? Shouldn't the explosion cause the momentum to increase since the explosion is really like force? I just don't see how this is possible. 2. Why does term Ʃ (m.sub i)(vector velocity of CM) dot (velocity of i relative to cm) = 0 in the total Kinetic energy for a system?? Some mathematical proofs and diagrams would be great!! I have provided a picture to show what I am talking about. I would really appreciate some explanations of this and this section. I am getting a little bit frustrated :( thank you. P.S. This is for my University Physics course.