Hi guys. I'd like to make an introduction somewhere but there doesn't seem to be a forum for that here. Basically Im an older student who, despite having low grades all throughout school, always loved science. I decided to go back to adult school to upgrade my marks and then go to university for geology. I'd like to discuss geology and career paths but I will do that on the other topics on this forum. So far Im doing alright in grade 12 physics. I've jumped into to grade 12 physics without grade 11 and its definitely harder than I thought, but of course it all depends on how much work you put into it. Everything is in the book and I've had no problem learning from that. Right now were on chapter 5 which is about the law of conservation of energy, keplers laws, planetary motion, stuff like that. I have no problems so far but when I do run into problems Il ask here. I do however need help with communication. I have 4 questions from my last test that just need an explanation but I only got half marks for them. My teacher said that if I can give her a better explanation for these question, she will give me these marks back, plus an extra 10 marks for having corrected everything on that test. (shes really nice like that haha) Il start with the first question Define "internal force" and "external force" and explain how these terms relate to the law of conservation of momentum. My answer: Internal forces are all the forces contained in a system where external forces cannot affect them. External forces are all the forces outside of a system. These forces relate to the law of conservation of momentum because if a system is not isolated and external forces can affect the internal forces of that system, they will affect the momentum of that system as well. I got only half marks for that. I guess shes looking for some algebra to prove it maybe, or in better words? Im not sure. Any advice/help on this this would be greatly appreciated.