As far I understand gravity holds the air back down, but surely it isn’t like a seal where air can’t escape
In: Planetary Science
Vacuum doesn’t “suck”.
The reason vacuum “sucks” in air on earth is because it’s surrounded by air under pressure. So to be more specific, the surrounding air forces itself into unoccupied space. It’s pushed, not pulled.
Once we establish principle, it’s easier to explain vacuum of space. Without anything else acting on it, the air on earth would like to push out and disperse too. But there IS something acting on it, pulling it down. The Earth, it’s gravity. It’s what’s causing the air to be under pressure in the first place, because that’s how gas resists being squished. It’s not pushing out, it’s just resisting being pushed down even more. That’s why air pressure drops the higher you go, until it transitions into the vacuum of space.
TL;DR There’s only one force acting on it, towards earth’s surface
Well, that’s ALMOST all. Light enough gasses, like hydrogen and helium, float to the very top of the atmosphere where they can be blown off by the solar wind. So earth loses a some atmosphere all the time.
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