Ok, so the other day I was chatting with a friend of mine, and this doubt came up... It is my understanding that hot air rises over cold air in the atmosphere because, being hotter, it is less dense and, hence, lighter. However, if we consider air as an ideal gas, doesn't that mean that the attraction between the molecules is negligible? If so, we could not really say that a mass of air is 'heavier' than another one, since gravity would pull on each of the molecules individually - as opposed to a solid object, where the molecules pull on each other and we can abstract their weight into a 'center of mass'.... Here each molecule is on its own, so how would it matter if a certain portion of air is less dense than another one? One possibility I imagined, discarding the 'heavier' or 'lighter' explanation, is that hotter air molecules have more kinetic energy so it takes a greater force to pull them down, and that because of this they tend to rise... But it is a guess mostly, and I have heard the 'heavier' gas explanation a lot of times, is there a way that it comes to terms with there being no attraction between the molecules? Please do say if I have not been clear and I will attempt to rephrase it better. I hope it is the right section to ask the question, bare with me please since I am new to the forum. Oh, and thanks in advance to anyone stopping by on this one.