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I will explain what I have done and my observations.

I took this bottle and added water into it.

1st time , 25 percent , then 75 percent and then 100 percent of water was filled in the bottle. Yes , water did not fall at any of the times. I turned the bottle and the water did not drip or fall.

1st time , there was almost 75% air inside the bottle with 25% water.That 75 % air is exerting force on the water and the weight of water itself and then the atmospheric pressure from outside. Even when air was 0% and 25% water didn’t fall.

I am not getting why didn't the water fall.

It doesn’t happen if I fill a tub of water and then turn it upside down or fill my water bottle or something else which has a shape similar to it.

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Please help me understand why it did not happen and how should we draw its FBD ?

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u can also slowly rotate the bottle.The water still does not come out.

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Now , Thank you all for your answers.I have attached this photo in which there is similar size bottle.From this water did drip , now how is that possible as well?It is almost similar.

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  • $\begingroup$ I really don't understand what you are observing, of what you are asking. So you file a bottle for 25% with water. Turned it around, and then the water stayed in bottom of the bottle (which is now on top), defying gravity?? $\endgroup$ – Bernhard Dec 29 '20 at 12:26
  • $\begingroup$ This is due to surface tension; en.wikipedia.org/wiki/Surface_tension $\endgroup$ – Adrian Howard Dec 29 '20 at 12:29
  • $\begingroup$ @Bernhard Yeah.I turned the bottle and the water did not drip.That’s it.What did you not understand sir ? $\endgroup$ – srijan Sri Dec 29 '20 at 12:45
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    $\begingroup$ Can you upload the photo of the bottle turned upside down ? I would like to see water not falling. $\endgroup$ – Danny LeBeau Dec 29 '20 at 13:06
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    $\begingroup$ Don't thank me, upvote instead! ;-) $\endgroup$ – Gert Dec 29 '20 at 13:50

There are two main possible explanations for the phenomenon you are reporting:

  1. Surface tension of water prevents it from exiting the bottle
  2. The atmospheric pressure prevents it from exiting

In the first case what is happening is the following: water has both adhesion and cohesion forces, meaning that water particles like to stick together and also like to stick with things they touch. Those are just properties of the water molecules. In your case water molecules really like to stick to the rim of your bottle, but they also want to stick to each other, so they form a film that needs a noticeable amount of force to be broken; and in your case turns out that the weight of the water in the bottle is not sufficient to break this film, so the water doesn't fall.

In the second case: our atmosphere is compressed by gravity, so it exerts force on everything it touches, this is how pressure in a stationary fluid work. Normally we dont feel it because the atmosphere exerts pressure in all directions, so the forces cancel out. But in your case if the water falls without letting air inside the bottle you create a partial vacuum inside the bottle, that doesn't exert as much force as the atmosphere, so the water gets pushed in by the atmospheric pressure and doesn't fall.

Of course your phenomenon is probably motivated not by only one of this two effects but by both effects working together. Consider also that surface tension is probably the cause of air not getting into the bottle.

To see if the explanation provided is correct I suggest you perform the following experiment: repeat the same experience, same bottle, same movements, same everything but this time mix a little drop of dish soap into your water before putting it into the bottle. Mixing soap into water will lower its surface tension strength dramatically. So if our explanation is correct you should see water dropping out of the bottle this time.

Of course this experiment is not an absolute proof of the correctness of our explanation, but it will help us to understand if we are on the right track!

  • $\begingroup$ Thank you so much for your answer sir.I have attached another photo of similar bottle from which water did drip.Please do check it $\endgroup$ – srijan Sri Dec 31 '20 at 11:29
  • $\begingroup$ The new bottle seem to have a wider neck. This is probably why water drips from it. As I mentioned in my answer this has to do with surface tension. Did you perform the experiment I suggested? If so be sure to share your findings! $\endgroup$ – Noumeno Dec 31 '20 at 12:40
  • $\begingroup$ 2 more cases @Noumeno , if it’s blood and oil instead of water, $\endgroup$ – srijan Sri Jan 6 at 19:35

Consider a 'normal' sized bottle, say half-filled with water. Now hold it upside down and notice how the flow isn't smooth at all, more like a 'gluck gluck gluck' start/stop kind of motion.

This is caused by the fact that not only does water have to leave the bottle but air has to enter it too, as otherwise a vacuum would form in the bottle.

Now when the bottle and its bottleneck are small flow is somewhat impeded (see Hagen Poiseuille flow) as it is and the atmospheric pressure outside and the partial vacuum inside the bottle stops flow altogether.

You can demonstrate this little 'theory' by inserting a bent straw into the upturned bottle, as shown below:

Bottle and straw

Now air can flow freely into the bottle through the straw (or tube) and water flow out of the bottle will be quick and smooth.

  • $\begingroup$ If it’s bottleneck is more in size than the bottle like tub.How does air enter into it like you have stated then sir ? $\endgroup$ – srijan Sri Dec 29 '20 at 13:29
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    $\begingroup$ What do you mean by 'in since', please? $\endgroup$ – Gert Dec 29 '20 at 13:31
  • $\begingroup$ this is what I meant.typo $\endgroup$ – srijan Sri Dec 29 '20 at 13:31
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    $\begingroup$ The wider the bottleneck, the easier water can flow through it (see Hagen Poiseuille and the influence of $R$). In a normal bottle a very partial vacuum forms when flow starts but that is then broken when air rushes past the water. What you get is a repeating cycle and that's what you observe for a normal bottle. $\endgroup$ – Gert Dec 29 '20 at 13:34
  • $\begingroup$ Hello sir, I have put another image of similar bottle just bigger in size.If you notice , from that bottle water did drip or fell. $\endgroup$ – srijan Sri Dec 31 '20 at 11:06

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