> Heh. This "bird flying in a cage" question seemed to bemuse the engineers at my work to no end. I think the question is impossible to answer if one does not realize that air itself has mass and exerts a downwards atmospheric force of 1 kilogram per square cm (14.7 pounds per square inch in the archaic system). Whenever it is flying, the bird pushes down on the air mass beneath itself with a force equal to its weight. That explanation, given in simple terms, seems clear enough -- but I'm still unhappy with the details of the actual dynamics/mechanics that I've heard so far.

Right now, the question is bemusing me to no end. I'd like to give this a test, but that is pretty much impossible for me at this time. Now, I realize that the air itself does have mass and that every time the bird flaps its wings it displaces the air underneath it which, in turn, could push down on the scale. What I'm not sure about is how exactly the air moves to the bottom of the cage. If it moved in a straight downward direction, then I'm sure that the added pressure on the bottom of the cage would equal to the bird's weight (and possibly even greater because the bird obtains an upward acceleration). I'm not sure that the air does move down in a straight path, however. If it did not spead out at all, I'm sure that we'd feel quite squished if an airplane flew overhead. So, I believe that some of the downward force changes into horizontal force as the air-under-high-pressure moved away from the bird. Since only the downward component of the force is measured by the scale, then the scale would read a decrease in weight, as some of the high-pressure-air would attempt to push the sides of the cage apart (although probably unsuccessfully).

-Ka"Maybe if I find a strong metal tube an a mini-heicopter...."z!