> > This whole thing reminds me of the conundrum, if that's the word, of the bird in the cage. If a bird is in an airtight cage attached to a scale and it starts to fly, will the scale read the same or less than before? I believe the answer is no as the bird still exerts downward pressure on the air below which in turn affects the scales.
> > Am I right in thinking this?
> >
> > Bea 'Materials science degree didn't really cover this' sty
>
> OK, I have NO IDEA on that one. Anyone else got something? (The principles seems sound... It's just very weird.)
>
> Don

Well, I'll see if I can take a whack at this. Let's see. I predict that, as the bird jumps up from the bottom of the cage to begin flying, the scale will first read more, as the bird exerts a downward force to push off. Also, every time the bird flaps its wings down, the scale will read more then before. When the bird move its wings up, however, I believe that the scale will read the same as just the bird cage, as the bird does not exert a downward force, as it would be in freefall for that small amount of time.

If the bird is high in the cage, however, I'm not sure if the downward push of its wings would equal the mass of the bird pushing down directly on the cage. In other words, I believe that if the bird is high in the cage, then the system with the flying bird will weigh less then the system with the bird just sitting there. I'll see how well I can reason this out.

If the bird is sitting directly on the cage, then its entire mass will add to the weight of the system, as gravity will act on the entire mass of the bird. At very low altitudes, the downward force exerted by the wings of the bird to keep the bird up must equal the force of gravity pushing the bird down. If the bird is flying low, all of this force from the wings pushes directly against the bottom of the cage, and thus affects the scales.

If the bird is in a high altitude however, I do not think that weight of the sitting-bird-in-a-cage and flying-bird-in-a-cage will be the same. As the bird pushes the air downward, it initially has the same force of gravity pushing the bird down, mostly due to the air's acceleration that the bird gave it. As the air directly below the bird interacts with more air farther away from the bird, however, the acceleration of the few particles of air becomes less, as the acceleration is now shared between more air particles. Some of the air particles may hit the sides of the cage, and the force will be used to make the cage move slighly left or right. After a while, when the downward force of the air reaches the bottom of the cage, it will not have nearly as much force as before. This is why we don't feel the sudden weight of a bird on our shoulders if one happens to fly high above us.

Well, that's my hypothesis anyway. I hope that you can figure out what I'm trying to say most of the time....I realize that my reasoning might be a bit convoluted.

-Ka"Great. Now where am I to find a bird and a really big completely air-tight cage to work with?"z!