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Simple Barometers & Air Pressure

  1. Apr 7, 2012 #1
    Hey Guys! I need help with interpreting something regarding simple barometers. I believe I understand what is going on relatively well, but I am having trouble figuring out what is going on when I adjust something.

    Mechanism: Barometer tube is a "vacuum" with no molecules inside of it. So when the Barometer with Mercury it is exposed to air pressure at sea level, the air pressure pushes down on the Mercury such that it is pushed through the tube up to a height of 760mm.

    Question: If I increased the surface area of the barometer cup from lets say a given [..I..] to [.......I.......], would the increased surface area of Mercury that air pressure can push on increase the height that Mercury moves up beyond 760mmHg?
    --> Considering Pressure is a force, wouldn't the increased surface area to exert a force on result in a stronger total force?

    Question: If I increase the radius of the barometer tube from lets say [..I..] to [..III..], would Mercury still rise to 760mmHg? I am confused when asking this because I am trying to reason how a whole column/layer of water in the ocean exerts only 1 atm of pressure on a diver when he is 10m below the ocean. I think this has something to do with how 1 atm of air pressure makes a water barometer rise to 10.3m, but does that reasoning also apply to the 10m column/layer of the ocean? (I hope this made sense... I just want to know the relationship between why 10m below ocean is 1 atm when the width/radius of the ocean is beyond that of a barometer tube)
  2. jcsd
  3. Apr 8, 2012 #2
    no,of course not,but for other reason...
    pressure is the same,1 atm,doesn`t matter the diameter of tube,but the mercury will fall due to his own weight,so it wouldn`t rise at760 mm...
    that`s why such tubes have tiny diameter,for the weight not to count...
    this pressure is made by gravity of the air,so gravity it`s the same,doesn`t matter the mass of the object,they are attracted with the same g to the earth...
    if you understand this,you understand the pressure problem as well...
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