When you punch holes in a bottle filled with water , it starts leaking but once you cap it ,it stops leaking. Why is that?
What’s happening here? Many things, but one big one is air pressure. With the cap screwed on, the water stays in the bottle. This is because the water needs more air to take the space at the top of the bottle, to replace the space previously filled by the water. Gravity is pulling on the water, and the water tries to flow out, but needs the air to expand and take up more space to do so. The air pressure isn’t changed – the air won’t expand or contract from the very small pull of the water. The air pressure is stronger than the pull of gravity. So the water stays in place.
If the cap is screwed on, there is nothing to replace any space used by the water. So the water doesn’t move. Unscrewing the cap allows air to flow into the bottle, which allows the water to pour out from the bottom, and the air takes up more and more space at the top.