Question for smart people. If you have a van (that weighs 1000kg), full of pidgeons, say 50kg and they are on the floor the whole van will weigh 1050 kg.

What happens if they are flying? Assume the van is sealed....

I'm not trying to be clever, we're having a big debate on this

Interesting question. Except I think it belongs in offtopic, unless these are somehow Swiss pigeons with little white crosses strapped to their backs.

My guess? A pigeon hovering inside the van must be exerting a downward force equivalent to its own body weight.

Therefore, the weight will still be 1050kg.

I agree. Now what if the van is open topped?

Dunno.

What about a practical experiment, say, off the top of Uetliberg?

Well providing that the pigeons stayed under the roof line then one could safely assume that the force of the air forced downwards by their wings would still exert pressure on the van floor so the weight would still be 1050kg.

Since you guys are obviously into such intellectual discussions, and since you work for the billing section of a certain carrier I think I'll be checking my phone bills more carefully from now on

what happens if we put you in the van and make you stand on a weighing scale.....then you jump up in the air.

Will you weigh the same when you land and will you land in the same place?

Or what if the pigeons were all "Brother Super Mario":

http://www.toppigeons.nl/en/nieuws.php?id=296

Well I hope you check ALL your bills carefully. Considering some of the shit that I have seen before

Weight is a mass * acceleration, which is usually g force downwards. If the bird is flying then it has accelerated upwards to exceed the force of gravity, so the weight acting downwards on the van through its centre of gravity will be minus the (landed) weight of the birds.

dave

was it from all the pidgeons?

and.......?

It depends how your pigeons are flying. If they were rocket-birds firing straight up, at the point of take-off their act of flying would cause a downward force on the floor of the van, sufficient to get them off the ground which would be about their weight. So at that point you would not notice any weight difference in the van.

However, birds fly aerodynamically driven by a forward thrust of a variable wing surface , so very little of their thrust is downward.....this means very little of their weight would be recorded if you weighed the van on a weighbridge as the whizz around the inside of the van on their way to Newcastle.

dave

As with an airplane, four main forces affect the flight of a bird: lift, drag, thrust, and the downward pull of gravity. To overcome gravity, birds must generate lift, the force that takes them upward. Air flowing over and under their specially-formed wing creates lift, but the airflow also pushes the wing back with a force called drag. When lift and drag are combined, an upward and backward force results. To overcome this, birds creates thrust by flapping their wings to move themselves forward.
HOW DOES A WING WORK?
A bird wing is very stream-lined, tapering from a thick, rounded leading edge to a thin point at the trailing edge. Because the wing is concavely curved, air traveling over the upper surface has to cover a greater distance and moves faster to catch up with air taking the shorter bottom route from the front to the back of the wing. This fast-moving air creates a low pressure zone along the upper surface of the wing. With low pressure above and higher pressure below, the wing is "sucked" up.

WING SHAPE AND USE
Birds with different types of flight have wings that are shaped very differently.
Many seabirds, like albatrosses, have long, narrow pointed wings for gliding long distances over the ocean into the ocean winds. The length generates lots of lift, while the narrow, pointed shape helps reduce drag while gliding.
Long, broad eagle wings have a large surface area for soaring on rising warm air currents. The spaces between the feathers at the end of the wing help reduce drag and are used for fine control at slow speeds. Storks, pelicans, and hawks have wings similar in shape.
Short rounded wings allow pheasants rapid takeoffs, good maneuverability, and short glides. Many forest birds have small rounded wings that are good for quick, sharp turns while flying among trees.
Similar to a high speed jet, swallows have relatively small, narrow, tapering wings. These wings can be flapped rapidly to provide speed with little drag. The fastest flyers in the bird world, falcons and swifts, have wings of this shape.

FLIGHT MOTION
Birds fly by flapping or gliding. Flapping takes tremendous energy, so many birds, such as jays and woodpeckers, follow bursts of flapping flight with gliding flight. Some larger birds have developed wings that let them soar and glide for long periods without flapping. Hummingbirds, with their tiny wings, can hardly glide at all.
On the upstroke of the wing beat, the feathers at the end of many bird wings twist sideways to let the air slip through with little resistance. The down stroke is the power stroke. Rather than rowing a bird through the air, the wings act like the propeller on an airplane to pull the bird forward.
Darting from flower to flower, hummingbirds fly like tiny helicopters. They can hover or quickly move forward, backward, sideways, straight up or straight down. Some hummingbirds flap their wings as many as 100 times per second to accomplish these maneuvers. Their unique shoulder joints also turn the wings upside down on the backstroke, enabling the wing's path follows a figure-8 pattern.

I think for the purposes of this rather silly discussion we would have to assume that our feathered friends are in a hover pattern and directing their force downwards. There wouldn't be enough space for them to get any forward motion

circles! If they're briefed thoroughly, I am sure this could work. After all, it's for a world record attempt isn't it?

i am one of the world record-holders for the number of people on a double bed. We did it on the Late Late Breakfast Show in 1988.

Boring but true.

dave

It would also depend upon how high our feathered subjects are hovering above the floor of the van. If they were close to the floor, they would have some of the benefits of ground effect and therefore exert more force on the floor of the van. If they are closer to the roof, this force would diminish as they begin to apply force to the resistance of the air itself. Also, they would not be flapping synchroniously, which, may result in some intermediate result.