First of all, buoyancy depends on gravity. If there is no gravity, there can be no such phenomenon as buoyancy. Look up the definition of buoyancy on Wikipedia or search buoyancy NASA on google, if you don’t believe it.
If gravity is simply buoyancy and density then why does hot air rise and not go down instead, or sideways? I’ll tell you why. Because we live in an environment where there is a downward force acting on things based on their mass. This can be experimentally verified and it does not depend on assuming the earth is a sphere. If I put 5 apples in a grocery scale I will get a certain weight (force). If I put an additional 5 apples of about the same size in the scale, the scale will register about twice the weight. So the force known as buoyancy depends on this downward force proportional to mass. This is why the deeper you go in a body of water the more pressure there is. This is why the higher you go in the atmosphere the less pressure there is.
Liquid water is nearly incompressible, so its density does not change much as you go deeper. In contrast, the atmosphere is made up of a mixture of gases, and they are very much compressible. So as you go up in the atmosphere, with the decreasing pressure the gaseous mixture becomes thinner or less dense because it is becoming less compressed.
If a mass of air were of the same temperature as the surrounding air, it would not tend to go up or down, because the upward forces around it based on decreasing pressure with altitude are balanced by the downward forces upon it based up its mass. But if the air were hotter than its surrounding air, its density would be less so that the downward force based on its mass would be less than the upward force due to decreasing pressure with altitude so the resulting balance of forces would cause it to rise. This is how a hot air balloon works.
Interestingly, forces greater than 1 g (i.e. 1 earth’s gravity) acting upon masses and proportional to mass can be artificially produced mechanically with centrifuges, or in an airplane in a steep coordinated turn, where a very steep turn may be alternately referred to as a high g turn, or pulling many g’s.
It was discovered today by T. Mark Hightower, formerly an engineer with NASA but now retired and actively engaged in flat earth theory research, that current flat earth theory implies that while one is present in one place on the flat earth they are actually at the same time also in two other far away distinct locations on the flat earth. (It may alternatively be possible that no one is actually present anywhere on the flat earth, but flat earth researchers consider this the null case where further study is not merited.) The ramifications of this discovery are far reaching for the fledgling resurgence of flat earth research in the recent past as many were hoping that flat earth theory would be a tremendous simplification of our understanding of God’s fish bowl in which we live, but now it appears that flat earth theory may be just as complex, enigmatic, and paradoxical, as Einstein’s theories of relativity, quantum mechanics, string theory, and multiverse theory, where our cozy fishbowl with the ceiling of a planetarium was erroneously viewed as being the result of a big bang billions of years ago resulting in an expansive and seemingly infinite multidimensional space time continuum containing countless galaxies, stars, black holes, planets, moons, asteroids, hemorrhoids, comets, explosive diarrhea, and aliens. Practical applications of these new discoveries are firmaments away, but some day it is hoped that the average Flat Earthian will be able to transport him or herself to other places within the flat earth fishbowl instantly and at will, thereby saving tremendous amounts of energy, and also making it unnecessary for NASA to continue faking the launching of satellites and other spacecraft, saving even more money and energy and improving NASA’s public image on Youtube, Facebook, and Google, and also making it much less likely that it will be necessary to target NASA employees in a future false flag incident possibly made to appear as if it were carried out by a lone nut Flat Earthian. Rigorous documentation of this discovery will be given in the near future (perhaps in a week or two) for peer review by fellow flat earth researchers, as well as conventional scientists and others.