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here is my question. Hope you'll help me ;-)

Consider a test-tube, almost completely filled with water, and closed with a stopper. Turn it over and then remove the stopper. If the diameter of the test-tube is small enough the water should not spill. I believe that the explanation is due to the fact that a loss of liquid would imply a larger volume for the air stucked at the top of the tube, which would imply a decrease of air pressure and this would act as a restoring force, opposite to the weight force of the water.

Am I right up to now?

My question is : how can i overcome that effect? I want to empty the tube so I believe I need to create air bubbles at the bottom interface. If I manage to create an air bubble, it will rise and then a volume of liquid is out of the tube.

My final question is then : what is the necessary pressure for the air at the bottom (or the necessary force) to overcome surface tension at the bottom to create an air bubble? Can you help me calculate that?

I hope my question(s) is(are) clear enough. Thank you for your answers.

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