if you release a helium balloon, it soars upward and eventually pops. explain this behavior. why does the balloon rise? the air pressure is lower the higher you go up. helium has a negative mass. the molecules in the balloon are very light and tend to move in the upwards direction more than to the sides or downward creating a net force on the top of the balloon that drives it upwards. the gas in the balloon is cooler than the air around it. some helium always leaks out the bottom (no matter how well you seal a balloon). this slowly pushes the balloon up. the gas in the balloon is warmer than the air around it. the gas in the balloon is less dense than the air around