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I have read about torricelli's invention of barometer,in that he used a test tube which he filled it fully with water and also he take a container and filled that container with some water.Now he inverts that test tube and put it inside the container and here he sees that not all the water in the test tube move into the container but some amount of water moved into the container creating a vacuum inside the test tube.Torricelli told that this happens because water pressure becomes equal to air pressure.And my question is how could water pressure be equal to air pressure as above water in the container there are so many air pressure?I am finding it confusing.If anybody want my question in visual prospect then please refer the link below https://youtu.be/EkDhlzA-lwI

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    $\begingroup$ Explain your question in the question - not all of us want to watch a youtube video to try and work out your question. $\endgroup$
    – user207455
    May 31, 2019 at 13:03
  • $\begingroup$ As it has been said if we move higher and higher then the pressure decreases but in this case water pressure was dominant to some case then as the water pressure increases it becomes equal to air pressure at some height why is that happening $\endgroup$
    – user230507
    Jun 1, 2019 at 7:12

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I assume the reason for your statement is you want to know how the demonstration in the video shows that water pressure equals air pressure. If that is not the case, you can disregard this answer.

Atmospheric air pressure is about 101,325 $\frac{N}{m^{2}}$ at sea level. The pressure of water as a function of depth with a vacuum above the water (in the video, the water in the tube with a vacuum above it) and at sea level is given by

$$P_{water}=ghd$$

Where $g$ = 9.81 $\frac{m}{s^2}$, $h$ is the depth in meters, and $d$ is the water density which can be taken as 997$\frac{kg}{m_2}$. Setting the water pressure equal to the atmospheric pressure gives us (9.81)(h)(997)=101,325. Solving for $h$ gives $h$ = 10.35 meters.

So the pressure at the bottom of the water column acting upward on the water outside the tube equals the air pressure acting downward on the surface of the water outside the column when the height of the column is about 10.3 meters, as demonstrated in the video.

Hope this helps

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