I was thinking about force lately, after reading some physics 100 questions on the internet to see if I have what it takes to become a physicist. For example, when you shoot a bullet, the chemical reaction that takes places exerts a force on the bullet for a short period of time (due to pressure). After that, the only force acting on the bullet is air resistance (slowing it down). However, isn't it also true that the bullet exerts a force on anything it may encounter? Such as say air molecules? (The bullet exerts a force on any air molecules it comes in contact with, losing energy as thermal and slowing down) What is the correct answer to a question like this one? How does this whole thing work? "A horizontally moving bullet slows down. Is anything exerting a force on it? How do you know? Is it exerting a force on anything? How do you know?" This isn't a homework question, its just something on the internet I'd like to know the answer to. How would one answer this question? Am I thinking too deeply about physics? Or is deep thought what is required? I would personally think this is the fact: It exerts a force on air molecules, or anything that it may encounter because air around the bullet moves. and Air exerts a force on the bullet, because the bullet slows down. EDIT: Also, any advice for someone looking to study physics?