6. Discussion
Variations of pressure and density, however slight, are necessary if a gas is to affect a scale and have measurable weight. In this respect a gas is very different than a liquid; an incom- pressible liquid will still have weight. From a pedagogical perspective the issue is compli- cated by the fact that macroscopically gases act like liquids in many respects. Specific to the issue discussed here if we were to perform the weighing experiment using a container without a lid or letting → ∞ h , equation (7), not accounting for temperature variation, predicts a weight equal to P A 0 . We should then interpret this result as the weight of the air column of area A extending to the edge of the atmosphere, that is, the weight of the air above the scale. The gas now exerts only a downward force on the scale which is consistent with common sense notions of weight, and would justify thinking of the gas like a liquid.
6. Discussion
Variations of pressure and density, however slight, are necessary if a gas is to affect a scale and have measurable weight. In this respect a gas is very different than a liquid; an incom- pressible liquid will still have weight. From a pedagogical perspective the issue is compli- cated by the fact that macroscopically gases act like liquids in many respects. Specific to the issue discussed here if we were to perform the weighing experiment using a container without a lid or letting → ∞ h , equation (7), not accounting for temperature variation, predicts a weight equal to P A 0 . We should then interpret this result as the weight of the air column of area A extending to the edge of the atmosphere, that is, the weight of the air above the scale. The gas now exerts only a downward force on the scale which is consistent with common sense notions of weight, and would justify thinking of the gas like a liquid.
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