So I was pondering this question: On a conceptual level, how does a perfectly spherical helium balloon rise? I understand that the density of helium gas is lower than that of our atmospheric composition of gases, but that is not giving the full perspective for me. On a molecular level, I feel like it WOULDN'T rise (despite my experiences in person). My logic behind this is: -A perfect spherical balloon has no net gas collisions with its container, as they are happening in all directions with equal force. -There is a pressure disparity between the helium and oxygen, but the atmosphere would be pushing equally over the entire surface of the balloon. No net pressure would imply that lift is not possible -Gravity is the only outside force that interacts with the spherical balloon (with no net pressure/molecular collisions). Thus, there is only a net downward force. I'm positive that the gas density disparity between helium and our atmosphere relates to this, but how does that work on a molecular scale?