It seems to me that those suggesting the weight remains the same can only do so by using an analogy that has two different fluids. Jed A1’s glass full of water and sand works with two fluids that have different weights but this is not analogues to the original question. To be so the glass and sand would be in a fish tank full of water, now swirl the sand around and what would happen to the weight of the glass? Having said all that a physicist friend of mine has read this thread and sent me the following:
“
The total mass of the aircraft when in flight is equal to the mass of the aircraft plus , the mass of its :
fuel
passengers
pilot
geese
water
poo in the toilet
and air in the cabin and holds.
The total flying weight of the aircraft is equal to the above total mass multiplied by the gravitational field strength, at that point in space above the Earth. Mass X Gravity (mg)
It does not matter whether the geese are asleep on the floor or on the wing. The total mass of the aircraft and its contents remains the same. Not strictly true because it is using fuel and losing mass and therefore weight every moment.
You might think that flying around the cabin removes their weight but this is an illusion.
Think of the birds as being suspended in a fluid filled tube such as some plastic beads in a jam jar of water.
As the birds fly there are many forces acting upon them:
frictional drag
Lift due to pressure difference as the air flows over their wings
Upthrust from the air due to the displacement of a mass of air
A weak gravitational pull between their own mass and that of the aircraft The forward thrust of their wings on the air
All of these forces will have equal and opposite reaction forces (Newtons ThirdLaw) at some point in this complex system.
They are all, however, relative to the air in the aircraft and the aircraft itself. As such they do not change the overall mass or weight of the system that is the aircraft in flight.
Hope this helps,
Clearly you are not busy enough if matters such as this distract you.”
He has a point in his last paragraph
