So imagine you are in a body of water: e.g a bath. You place a clear container in the water, like a jug, and fill it up. When you then invert the container and slowly rise it above the surface, why does the water stay inside the container until the container breaks the surface?
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If the water were to start falling out of the jug the moment the water level in the jug met the water level outside of the jug there would be nothing to fill the void left behind the water. Nature abhors a vacuum and won’t allow a low-pressure bubble to form behind the water when it can keep that area filled with water instead. The weight of the water in the jug is supported by the water in the bath and won’t fall out until you break the surface and atmospheric pressure isn’t enough to hold that much water in place against vacuum potential.
That’s also the reason pouring water out of certain containers with small mouths glug. As the water falls out air has to push its way in to fill the vacuum forming behind what you’re pouring out.
In some ways it’s a form of hydraulics, applying a small force over a large surface area to get a large amount of force over a small surface area. The bath has a lot of surface area with small atmospheric force pushing on all out and that provides enough force when the container’s opening is smaller relative to that surface area that it can resist the pull of gravity on the amount of water above it in the container.
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