Discussion on question by sociocat: If you open a 1ft-diameter portal between Earth and space, how fast will the air rush through?

@KevinKeane Forget about gravity altogether, it’s not relevant to this question. All that matters is the difference in pressure. The pressure at the Earth end happens to be caused by gravity acting on the atmosphere, but that doesn’t matter — the answer would be exactly the same if the Earth end was replaced with a big sealed pressurised box in zero G.