What Is the Maximum Height Air Pressure Can Support?

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SUMMARY

The maximum height that atmospheric pressure can support a column of liquid, such as water in a straw, is approximately 760 mm of mercury or about 30 feet of water. This phenomenon is explained by the force exerted by atmospheric pressure, which is around 10^5 Newtons per square meter. When the top of the straw is sealed and the straw is removed from the water, a pressure differential is created that generates an upward force sufficient to counteract gravity, allowing the water to remain suspended. The viscosity and surface tension at the bottom of the straw play crucial roles in maintaining this pressure differential.

PREREQUISITES
  • Understanding of atmospheric pressure and its measurement (e.g., 10^5 Newtons per square meter)
  • Basic knowledge of fluid dynamics, particularly pressure differentials
  • Familiarity with the concepts of viscosity and surface tension
  • Knowledge of barometric measurements (e.g., 760 mm of mercury)
NEXT STEPS
  • Research the principles of fluid dynamics and pressure differentials in liquids
  • Explore the concept of barometers and their role in measuring atmospheric pressure
  • Learn about the effects of viscosity and surface tension on fluid behavior
  • Investigate the physics behind suction and how it applies to drinking through straws
USEFUL FOR

Students of physics, educators explaining fluid dynamics, and anyone interested in the principles of atmospheric pressure and its effects on liquids.

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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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