What Is the Maximum Height Air Pressure Can Support?

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Discussion Overview

The discussion revolves around the maximum height that atmospheric air pressure can support a column of liquid, specifically in the context of using a straw. Participants explore the physics behind how air pressure can lift liquid and inquire about the limits of this phenomenon.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that atmospheric pressure exerts a force on surfaces, including the water in a straw, and provides a rough estimate of atmospheric pressure as ~10^5 Newtons per square meter.
  • Another participant explains that the ability to suck liquid through a straw is due to the pressure differential created when the top of the straw is sealed and the pressure inside is reduced.
  • A participant describes the mechanics of how water is held in the straw, mentioning the roles of viscosity and surface tension in preventing air from entering the straw from below.
  • There is a request for clarification on the maximum height that can be supported using this method, with one participant suggesting a height of 760 mm of mercury or about 30 feet of water.

Areas of Agreement / Disagreement

Participants express curiosity about the maximum height that air pressure can support, but there is no consensus on a definitive answer, as some participants provide estimates while others seek further clarification.

Contextual Notes

Participants reference specific measurements and concepts related to atmospheric pressure and fluid dynamics, but the discussion does not resolve the maximum height definitively, leaving room for further exploration.

Who May Find This Useful

This discussion may be of interest to those studying fluid dynamics, atmospheric physics, or anyone curious about the principles of pressure and liquid columns in practical applications.

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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
 
Last edited by a moderator:

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