So I’m aware it’s because of pressure difference, but why does that matter? Why does the pressure try to equal out immediately and not just slowly wait as things move into it like they would in ambient pressure?
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With nothing in the hole to push back, why wouldn’t the surrounding ambient pressure force into the gap?
You seem close to the logic, but I guess the answer would be because pressure is really strong, and things are really weak.
If you created a vacuum and put a plank of wood across it, the plank probably wouldn’t get sucked in because wood is strong. But don’t downplay the *strength* of air pressure, at sea level it’s roughly 15lbs per square in.
Imagine a 15lb weight on a piece of wood, pretty strong. Put that weight on a balloon and it’ll pop instantly, gases are really weak.
So not everything *floods* into a vacuum, weak materials will yes, but under strong enough pressures solids might too.
Individual molecules move randomly. But random motion will average out to filling the vacuum because there is less resistance that way. Say you are an air molecule at the outlet of a pressurized tank in space. Behind you there are billions of angry other air molecules. If you go that way, there’s a good chance you will hit one and get sent flying back out. In front of you there is empty space. So on average way more air molecules will be moving out than in.
It’s easier to picture if you don’t think of it as the vacuum pulling things in, but as everything else trying to push things out. Gravity is pulling all of the air (or water, etc.) down, which makes it all squish together near the ground. All of the air has other air all around it pushing on it.
At normal pressure this means the air mills about, bouncing off the other air and moving a little when it finds some less crowded space. A vacuum has (almost) no air, which means that the air next to it has a lot of push on one side and no push on the other. All of that other air pushes it into the empty space until it fills up, and then it has air pushing from all sides again.
Pressure in a gas is the force of the molecules bouncing around and hitting the sides of the container.
Logically, a higher pressure means more molecules or faster bouncing around, so if the container suddenly expanded then a higher pressure would more quickly expand with it to fill the new empty space.
Even if the individual molecules aren’t any faster, because more of them are bouncing around, more of them move into the new space, and it fills faster.
The actual physical speed that the individual molecules expand into the new space depends on their original speed, and so their temperature. At room temperature, this is around 300 or 400 meters per second. Almost no matter the pressure, at this temperature the gas will spread out at this speed on average.
Air is a bunch of randomly moving particles. They bounce (sort of) off each other and the container all the time, and when you put a hole in the container, the ones that’d bounce off the container there instead go out. Since now they’re not in their original location, others can spread out to there, and subsequently outside.
With ambient pressure, the leaving particles are replaced, for the most part, by the particles coming in from outside, so you don’t have a massive move towards the hole.
Remember what pressure actually *is*. It’s the physical effect of the atoms of the gas pushing against each other and the boundaries of their container or against the boundaries of an area of different pressure.
The reason why things would move slowly when pushing against something with ambient pressure is because of that ambient pressure, it’s pushing back. A vacuum has no pressure so there is nothing to push back or stop something else flooding in.
At ambient pressure, air molecules are flying around at high speed, constantly bouncing against the walls and into each other. If you have a cloud of gas, its molecules will try to fly outward, but are soon bounced back into the cloud by the air molecules around it, and only slowly this random back-and-forth will lead to the cloud dissipating into the air around it.
If the cloud neighbors a vacuum though, there is no resistance at all in the direction of the vacuum. Any molecule that flies into the void will just keep flying until it hits the opposite wall, so the vacuum will fill up quite fast.
As an analogy, imagine you have a pawn on a chessboard, and you repeatedly throw a coin. At heads, you move it one row forward, at tails, one row backward. That’s the random motion of a gas cloud at ambient pressure. You will eventually reach the other side, but it will take a while. Now you do the same, but tails don’t count. That’s the expansion into a vacuum; you will reach the other side way faster.
Imagine a little ball floating through space. Theres nothing else around, so it will keep floating in the direction it’s moving. That’s no pressure/vacuum.
Now let’s say we have a bunch of balls moving in random directions. Occasionally they’ll bump into each other, and they’ll both change direction. That’s pressure/an atmosphere. The more stuff you put into a small area, the more they crash into each other, and the more they change direction.
Now put a vacuum next to a pressurized atmosphere. Anything that moves INTO the vacuum will keep pushing moving forward. But if a ball tries to move OUT of the vacuum and into the atmosphere, its going to crash into all of the other balls that are bouncing around. Since it’s easier to move INTO the vacuum than to get back out, it looks like everything gets pulled in.
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