# Why is it that when you put a small hole on a bottle that is close, the water inside doesn’t come out but if you open the bottle cap, the water goes out?

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Why is it that when you put a small hole on a bottle that is close, the water inside doesn’t come out but if you open the bottle cap, the water goes out?

In: Physics

Small hole on the bottom.

If water comes out of the bottle, something needs to replace it, in this case air.

If the hole is to small to let air past, the water won’t come out because air can’t get in the bottle, so the vaccum pressure holds the water in.

When you open the cap, air can get in to replace the water through the opening on top, so the water flows out.

When water comes out of the bottle something needs to replace it, this is typically air. When you open a small hole at the bottom there is no chance for air to enter the bottle, if water came out then there would be a vacuum at the top of the bottle. When you remove the cap air can rush in and allow the water to fall out the bottom.

An important factor that the other comments did not address is *surface tension.* Water likes to stick together, and so it takes effort to separate a stream of water from a body of water. If the hole is small, the water behind the hole sticks together enough that it doesn’t let any air bubbles past it through the hole, so not enough effort is exerted to separate any water. Unscrewing the cap = air pressure from the atmosphere coming down hard on the water from above, which is enough to overcome the surface tension.

Another type of effort that would overcome this would be squeezing the bottle with your hand, although with not enough air coming in quick enough to replace the water as it exits, the bottle would just stay crumpled inward until you opened the cap.