What Is the Maximum Height Air Pressure Can Support?

AI Thread Summary
Atmospheric pressure exerts a force on surfaces, allowing liquids to be suspended in straws due to pressure differentials. The pressure is approximately 10^5 Newtons per square meter, enabling the water's weight to be countered by this force. When the top of the straw is sealed and lifted from the water, a pressure drop occurs, creating an upward force that opposes gravity. The maximum height that atmospheric pressure can support water in a straw is around 760 mm of mercury or about 30 feet of water. This phenomenon illustrates the principles of fluid dynamics and pressure differentials in action.
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Check this video.
How physics explains that? I know that it is because of atmospheric air,but I want more specific explanation.

Thanks!
 
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The air pressure leads to a force on every surface, including the surface of the water inside the straw. Atmospheric pressure is ~10^5 Newtons per square meter, which is probably around 1 Newton for the cross sectional area of a straw. The weight of the water is less than 1 Newton, so the force from atmospheric pressure is sufficient to keep the water suspended in the straw.
 
it works for exactly the same reason you are able to suck liquid through a straw --- have you thought about that. I mean, if this puzzles you, why are you not puzzled that you can drink soda through a straw?
 
After the top of the straw is sealed, and as the straw is removed from the water, some of the water flows out the bottom of the straw, expanding and reducing the pressure of the air between the sealed top of the straw and the surface of the water inside the straw, and the pressure differential between the ambient pressure air outside the straw and the reduced pressure air within the straw generates enough upwards force to oppose gravity. The viscosity and the surface tension at the bottom of the straw "seals" the bottom of the straw well enough to prevent air from flowing up through the water inside the straw from below.
 
okay, people who answered this, tell me this. what is the maximum possible height which is can hold using this method.
 
oneomega said:
okay, people who answered this, tell me this. what is the maximum possible height which is can hold using this method.

760 mm of mercury or about 30 feet of water.

http://www.thermospokenhere.com/wp/02_tsh/B080___torricelli/barometer.png
 
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