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Like a Bird on a Wire

Segment from the helicopter documentary "Straight Up!", showing power line maintenance being performed on live wires by a man outside a ...

Balance- A Bird Sitting In A Wire Cage Which Is Hanging From A ...

When the bird is not flying, the scale would register the [b]weight of the cage and the weight of the bird.[/b]

Now when the bird flies, while still inside the cage, the air "lift" produced by the wings of the bird sustains the weight of the bird.[b] The floor of the cage does not bear anymore the weight of the bird.[/b]

This argument holds through even on other cases. Now consider, if an airplane flies directly overhead, will we feel its weight?

This is from Arshad's link http://answers.yahoo.com/question/index?qid=20090724204859AAxic4V

I din't understand hoe wt is same in both ( bolded ) cases Thanks Arshad

[i]"If the bird is flying, the bird is pushing down on the air. The air is pushing down on the cage.

If the bird is not rising, the weight of the cage should be approximagely the same whether

the bird is resting or flying. If the cage were very small, some of the force might be

dissipated to the earth, but we're talking first-order effects, here."[/i]

My Doubt : Shud we consider the weight due to the air pushed down by the bird's wings??

there are two cases for this problem....at least according to me...
CASE 1) when the cage has a solid base which can stop blowing air....
so when the bird is sitting quietly the normal reaction on the bird is balanced by its weight. as the same normal force is given to the cage, and spring balance gives an upward force kx....so
kx[ss]1[/ss]=mg+m'g

now the bird starts flying the air is pushed down so that the bird gets a reaction force m'g upward....now this air strikes the base of the cage with same force...thus net downward force is again mg+m'g
so kx[ss]2[/ss]=mg+m'g

so kx[ss]1[/ss]=kx[ss]2[/ss]
or,x[ss]1[/ss]=x[ss]2[/ss]
so same reading.. CASE 2) when the cage has a grill base through which air can pass....
for bird at rest same logic holds good..
so kx[ss]1[/ss]=mg+m'g

now when the bird flies...

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