Hey All, This is my first post and I'm glad I joined. It looks like a lot of good advice is given around here. Anyway, on to my problem: If only an external force can change the velocity of a body, how can the internal force of the brakes bring a car to rest. This question totally stumps me. I'm not really sure what I am supposed to be doing at all. I am not sure exactly what forces are being taken into account, and I'm not sure what my answer is supposed to be. I'm pretty lost. I'm not necessarily looking for an answer, as much as I am looking for a little bit of explanation or clarification.