"Extreme situations" in physics problems I don't know if this question is pertinent for this discussion forum. I was making some study notes, and i was trying to recollect statements that are always "extreme" in physics problems (such as mechanics). Until now, i have found two of them: Lose contact with the ground (the normal force is 0), and rope goes slack (tension force is 0). I was wondering, are there any other "extreme situations" that i should be aware of? Thank you very much for your time.