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  #22  
Old February 1st 04, 08:22 PM
Peter Duniho
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"G.R. Patterson III" wrote in message
...
In an airplane, air is pushed down to support the plane and it's contents,

so
the pressure on the Earth's surface doesn't change. I'd say that makes it

"the
same weight". I don't know if one can say the same about people in lighter

than
air craft.


Of course one can. In a lighter-than-air craft, the aircraft is still being
supported by the air underneath, which transfers that load to the Earth.

There are ways to nitpick the question, considering things like angular
momentum and inertia -- after all, it's true that since the air doesn't
provide a rigid connection, there are theoretical ways to demonstrate that
the Earth's total mass *does* change -- but then in those cases, anything
not firmly anchored to the planet could be considered not part of the total
mass of the planet, and thus the fact that the hypothetical people are in
the air is irrelevant. The Earth would have been "that much lighter" the
instant they were not firmly anchored to the planet (say, on the walk across
the ramp to the airplane).

Pete