I believe the poster was suggesting that because the bird was converting calories to other forms of energy (ultimately, being lost as heat energy), the weight of that caloric source would be lost to the system in question.- can't see what you're getting at here.Quote:
but
the bird is expending energy so it also makes sense if the box would weigh less the same as if I expended energy in lifting the box or if I was in the box then jumped up. As I came down I would be pressing the molecules beneath me but not on the way up so the box would weigh less, at least on my ascent
Correct which is why a birds wings are so difficult to engineer in a lab but my point remains that the upstroke is the reverse of the downstroke only to a lesser degree but so the box should weigh less on the upstrokeNow, when a bird is flying by flapping its wings, you are correct that the bird is only pushing downwards on the air when the wing is travelling downwards. If the bird were to move as much air upwards on its upstroke as it moves downwards on its downstroke, the bird would never get off the ground. The bird must be sure to angle its wings to move as little air as possible in the wing's upstroke, and to move as much air as possible on the downstroke..
Yes, the size of the box does matter. Because air pressure is highly variable..
They should have stood in the box themselves then jumped upas to what the Myth busters demonstrated, well, there are many flaws. The size of the box relative to the size of the bird is one. The large number of birds is another. They would have done better to create a cage large enough for a bird to fly, out of light wire and saran wrap, suspended from a scale to measure a dynamic load.
No. Air is not a perfect spring, which is what you are modeling.I disagree. The pressure caused by the wings is dissipated over a greater distance the bigger the box and while its force on any given point is less the force is simply spread out further so the accumulative effect is the same
That is because air can be compressed which is why they use oil in hydraulics instead of airNo. Air is not a perfect spring, which is what you are modeling.
Put a piston at one end of a tube, and you'll see the air pressure at the head of the piston increase and decrease as the piston moves. If the tube is short, you'll see the air pressure change at the other end of the tube as well. But if the tube is very long, you will not see any change in the air pressure at the far end of the tube as the piston moves.
Or, to your point as the area is increased, put a piston at the narrow end of a funnel and you'll see the air pressure change at the wide end of the funnel as the piston moves. But if the wide end of the funnel is very far away, the air pressure will not change at the far end.
LOL...now we have nuclear reactions. If you have any mass being converted to energy through the formula e=mc2 let me know...I want to be a long long ways away from that bird and box.Correct which is why a birds wings are so difficult to engineer in a lab but my point remains that the upstroke is the reverse of the downstroke only to a lesser degree but so the box should weigh less on the upstroke
My other point is that the bird is expending energy and energy can move weight as well as become mass e=mc2
So when the bird expends energy by flapping its wings this energy has the capability of moving the container and does so slightly on the up flap by pushing molecules against the roof and forming a vacuum beneath itself which makes the container weigh less
No.That is because air can be compressed which is why they use oil in hydraulics instead of air
but the energy created by the birds wings is not lost just dissipated you seem to infer the energy is lost and if the energy is absorbed by the compressing air there is a equal reaction somewhere
