Why doesn't a barometer with vacuum get crushed by the atmosphere?

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A mercury barometer does not get crushed by atmospheric pressure because the external pressure is balanced by the weight of the mercury column, which is held up by atmospheric pressure. The barometer's strong glass or metal shell can withstand this pressure, unlike weaker materials that would collapse. The vacuum inside the barometer does not exert pressure; it is simply a space devoid of air, allowing the mercury to remain at a static level. Additionally, the strength of cylindrical shapes contributes to their ability to withstand uniform compressive loads. Understanding these principles clarifies why barometers function effectively without being crushed by atmospheric pressure.
  • #31
Atmospheric pressure exerts a 14.7 pounds per square inch at sea level. Making 1 sq inch of glass withstand 14.7 pounds isn't very hard (Or 1/4 inch per side = less than 1 lb)

Say you have 2 shallow cylinders of 1 foot diameter = 113 square inches with a vacuum between them. That means it will take 113x14.7 = 1661 lbs to separate them.
 
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  • #32
sophiecentaur said:
Yes. There are good mathematical models of materials and structures but, from what you say about your technical knowledge, you may find them hard to follow. Perhaps, if you googled terms like ' strength of a beam' you could see if you find the maths in that example accessible.
This is non-trivial stuff and needs to be approached from basic principles and not jumped into, half way through.

Thank you very much for your suggestions.
 
  • #33
meBigGuy said:
Atmospheric pressure exerts a 14.7 pounds per square inch at sea level. Making 1 sq inch of glass withstand 14.7 pounds isn't very hard (Or 1/4 inch per side = less than 1 lb)

Say you have 2 shallow cylinders of 1 foot diameter = 113 square inches with a vacuum between them. That means it will take 113x14.7 = 1661 lbs to separate them.

Thank you very much. That was an excellent use of mathematics.
 

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