1. The problem statement, all variables and given/known data When the air rush out of a balloon, it shoots out. What physics principle is responsible for this behavior? 2. Relevant equations 3. The attempt at a solution Is it due to Newton's 2 nd law or 3 rd law?? We can compare this to a rocket propulsion. We can explain this using Newton's second law (conservation of momentum when Fnet = 0). However, it is true only if net force = 0. But we know that the balloon also will shoot up, if the balloon's open end is pointing down. How do I explain this because now force of gravity is acting on the system.