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I was washing the dishes and came across a situation that was counterintuitive (at least from my perspective). The situation consisted of a bowl of water and a filled bottle of water. When I dip only the tip (opening) of the water bottle into the bowl of water, the water from the bottle does not flow out into the bowl. On the other hand, once the bottle is raised just enough so that the opening in the bottle is above the bowl of water, the water then obviously flows out into the bowl.

Below is a picture demonstrating the situation.

enter image description here

My Question

Would this phenomena change depending upon which liquid(other then water) is used?

Or more specifically could the surface tension properties of another liquid differ so much from water where a observable difference would occur in this situation?


marked as duplicate by Community Aug 3 at 3:19

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The liquid does not flow out because doing so will create a vacuum at the raised end of the bottle. There is no way for air to enter the bottle to fill the raise end. The pressure difference prevents this from happening. This is not dependent on the liquid used.

  • $\begingroup$ So why doesn't the water flow out and then the bottle gets crushed by the atmospheric pressure? $\endgroup$ – Cabbage Champion Aug 2 at 17:35
  • $\begingroup$ Just a small vacuum creates a pressure difference that is stronger than the pressure difference between the raised part of the water in the bottle and the pressure of the water at the top of the tank (atmosheric pressure). You can put a piece of cardboard on the top of the bottle, hold it on tight, and turn bottle upside down. Remove you hand from the cardboard and it will stay in place and no water will leak out. This is the same principle. $\endgroup$ – jmh Aug 2 at 17:47
  • $\begingroup$ @CabbageChampion So simply said, The pressure inside is 0 atm (vacuum), and the pressure outside is 1 atm. The force pushing the water would be much greater than the gravity to the water inside the bottle, making it unable to escape. $\endgroup$ – Matthew Roh Aug 2 at 19:05

This situation is in fact sensitively dependent on not only the liquid being used but also the diameter of the opening in the inverted bottle. Here is why.

For water to run freely out of the bottle neck requires that air simultaneously enter it in the opposite direction. This requires the bottle neck to support what is called two-phase flow, which requires that the surface tension of the liquid be relatively low and the diameter of the neck be relatively large, compared to the density of the fluid and the magnitude of gravity. There is a nondimensional scaling law (whose name I cannot remember right now) which allows the transition point between one-phase flow (called slug flow) and two-phase flow to be estimated for any values of surface tension, density, neck diameter and gravity. I invite the experts here to help me remember the name of that scaling parameter!


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