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The buoyant force of air? Concept question

  1. Aug 15, 2012 #1
    if we weigh a metal object which is immersed in water, we have to correct the buoyant force for water. Air is a fluid. Why don't we correct for the buoyant force of the air when we weigh it in the air?

    What i think it may be is because we have a set atmospheric pressure being 1.013 Kpa in the air and we measure everything in relation to the world relative to that?

    Can someone discuss why this is, I'm not sure what i said onto is a logical quick explanation, but there should be much more to this?
     
  2. jcsd
  3. Aug 15, 2012 #2

    AlephZero

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    The density of air at sea level is about 1/800 the density of water, and the buoyancy correction for weighing most objects in air is small (less than 0.1%). The correction is applied when weighing objects very accurately.

    Of course if the object being weighed has a density of the same order of magnitude as air (e.g. an inflated balloon) the correction is not negligible!
     
  4. Aug 16, 2012 #3

    CWatters

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    ..especially a balloon inflated with helium.
     
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