If someone was to weigh a lorry full of birds, would it weigh more to have all the birds on their perches, or all the birds flying?
2006-09-01 05:48:24 · 22 answers · asked by Matt S 2 in Science & Mathematics ➔ Mathematics
Balance of forces question.
When perched, you get the full force of gravity on each bird transmitted through the perches to the frame to the chassis to the wheels to the weighbridge.
When flying, the birds counteract gravity by creating a momentum change in the air around them. The act of creating that momentum generates a force which is equal and opposite to the gravitational force on the bird, if it is hovering, or it may have an additional horizontal component if it is travelling. But that isn't a concern.
The air flows downwards, and the floor of the truck creates another momentum change, which means there must be a force on the floor. In a frictionless universe and a sealed truck, that would be equal to the force acting on the birds, so the truck would weigh the same. But in real life some air leaks out the sides, and some energy is turned into heat by friction in the air, which reduces the momentum and thus reduces the force on the truck.
So with the birds flying, it weighs less. Note: energy is conserved, momentum is not.
2006-09-01 05:49:54 · answer #1 · answered by wild_eep 6 · 4⤊ 0⤋
They weigh the same. It's a closed system. When the birds sit on their perches, the perches support them. When the birds are flying, the air supports them. Assuming that the lorry is airtight, which it generally is in these physics problems, there won't be a weight difference.
2006-09-01 13:59:44 · answer #2 · answered by TychaBrahe 7 · 0⤊ 0⤋
The weight of the birds are always the same whether they are flying or not...
If you weigh the birds on the perches it would weigh more because the perches have a weight too...
2006-09-01 12:56:28 · answer #3 · answered by princessin_bluejeans 2 · 0⤊ 0⤋
this is a new slant on an old question which weighs more a ton of coal or a ton of feathers(any idiot knows a ton is a ton no matter what the product is)..however if all the birds were FLYING inside the lorry( big bloody lorry)..then the fact that they are airborne means that they cant be included in the weight of the lorry( same question as does the space shuttle weigh more with astronauts strapped in or less floating free..isn't it? please don't get technical about space causing weightlessness..it is a rhetorical question
2006-09-01 13:04:16 · answer #4 · answered by hondanut 4 · 0⤊ 0⤋
In theory: If the cage is completely closed airtight and if you weigh the cage with bird in it fly or not the weight will be same. In all other situations the weight should be different but the bird weight will NOT necessarily be zero.
2006-09-01 13:18:00 · answer #5 · answered by Dr M 5 · 0⤊ 0⤋
if they were flying.
if the birds were flying there would be no extra weight on the lorry because they would be in the air. the only downforce would be the air being pushed down by their wings
2006-09-01 12:57:39 · answer #6 · answered by Anonymous · 0⤊ 0⤋
if the birds were flying they wouldnt weigh anything as they float
on their perches would give you the weight
2006-09-01 12:50:10 · answer #7 · answered by ryn 4 · 0⤊ 1⤋
birds on perches not much of a puzzle
2006-09-01 16:29:04 · answer #8 · answered by mm_uk_2005 2 · 0⤊ 0⤋
It's not experimentally possible to weigh birds that are flying. It's a contradiction of terminology to assume that you can.
2006-09-01 12:56:54 · answer #9 · answered by _scientist 2 · 0⤊ 0⤋
On there perches, because flapping wings create air not weight
2006-09-01 16:34:57 · answer #10 · answered by Anonymous · 0⤊ 0⤋