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Bird in a box

Discussion in 'CycleChat Cafe' started by cisamcgu, 14 Aug 2007.

  1. cisamcgu

    cisamcgu Veteran

    Location:
    Merseyside-ish
    This may have been posted before, if so, please ignore :sad:

    A box weighs 1000g
    A canary weighs 10g

    Put canary in box, and then weigh them. Total weight = 1010g

    Canary starts to fly in the box (OK, rather tricky, but bare with me) - what is the weight now ? (I think still 1010g)

    Now, leaving the box on the scales, open the lid of the box, but let the canary land on the floor of the box. What is the weight now ? (I think still 1010g)

    What happens if the canary flies, but stays within the open box ? What is the weight then ? 1000g ? 1010g ?

    What happens if the canary starts to leave the box, but stays very close to the open lid ? (I have no idea about this bit ;))

    Any thoughts ?

    Andrew
     
  2. chris42

    chris42 New Member

    Location:
    Deal, Kent
    the answer is 42
     
  3. Arch

    Arch Married to Night Train

    Location:
    York, UK
    You are Mr Hippo, and I claim my five pounds.

    Hmm. Depends. Do you want the total weight of the items, or the weight shown on the scales.

    I don't see how the weight of the canary registers if it's flying. If it's sitting on the floor or the edge of the box it counts, if it's flying it doesn't, because it's not exerting a pressure on the scales. It still weighs 10g or whatever, but it's not on the scales.

    So, in terms of weight displayed on scales, it'll be a) 1010g, ;) 1000g, c) 1010g and d)1000g.
     
  4. alecstilleyedye

    alecstilleyedye nothing in moderation Staff Member

    what if the canary poops in the box?
     
  5. Tetedelacourse

    Tetedelacourse New Member

    Location:
    Rosyth
    Arch is right i think.
     
  6. cisamcgu

    cisamcgu Veteran

    Location:
    Merseyside-ish
    lol - I'm not Mr Hippo ;)

    No, I ask it because I was on hoiliday last week (in The Netherlands - marvellous cycling country; rather flat, but so, so civilised), and mentioned the "plane on a treadmill problem" to a friend. He replied with the "bird in a box" - which I still cannot get my head around. When you open the lid, does the weight change ????


    Andrew
     
  7. Mr Celine

    Mr Celine Discordian

    Location:
    Under a cloud
    The gram is a measure of mass and not weight. The mass of the box includes the canary, the box and the air inside it so does not change.

    The weighing scales are showing the effect of gravity on that mass. I don't think that a canary can hover, but if it can then the air it pushes downwards to maintain its hover will have the same effect on the scales as if the canary was perched in the box.
     
  8. cisamcgu

    cisamcgu Veteran

    Location:
    Merseyside-ish
    But the mass of the box+canary must be the same even if the canary is in the air of not. Surely conservation of mass must still be true, otherwise where has the mass of the bird gone ?
     
  9. Mister Paul

    Mister Paul Honky

    Location:
    North Somerset
    When you open the lid, the weight doesn't change if the bird is still standing in the box. It changes when he flies off.

    The weight of the bird doesn't count if it is flying, as weight is force of gravity, and a flying bird's actions counter this force.
     
  10. Arch

    Arch Married to Night Train

    Location:
    York, UK
    Not unless the wings of the canary form an airtight seal with the box surely, and the pushed down air will escape up and around the wing? I don't think the downdraft of a canary wing would exert enough force to affect the scales, unless they were extremely sensitive.

    What about if there are 3 canaries, on a treadmill....
     
  11. Mister Paul

    Mister Paul Honky

    Location:
    North Somerset
    I'm not sure now. Apparently Mythbusters did it with birds, and with a helicopter, and there was no change when they were flying. And they are never wrong.

    Mind you, there is a point when flying a helicopter when the air forced downwards bouncing off the ground counters the lift created by the rotors. Or summat like that.

    But I don't care. Physics is all a load of guff anyway. Sometimes. But I never said anything.

    I think the 4 quarter pounders I just ate have addled my brain.
     
  12. bonj2

    bonj2 Guest

    The scales aren't measuring mass, they're measuring weight.

    The only 'mysticism' associated with this apparent conundrum relies on the reader not understanding the difference between mass and weight. Which no offence cisamcgu but you obviously don't.
     
  13. Cycling Naturalist

    Cycling Naturalist Legendary Member

    Location:
    Llangollen
    I hate to disagree with the fair Arch, but the box is a closed system and when the canary takes off, it can only do so by exerting enough pressure with its wings to overcome gravity. In other words it forces air downwards to the bottom of the box which will register as weight if the box is weighed. The weight will be less than 10g though because of the effect of turbulence as the down draught is dissipated.

    If you don't believe me - think of a rocket taking off and the effect of the blast on the launch pad.
     
  14. Mister Paul

    Mister Paul Honky

    Location:
    North Somerset
    The scales aren't measuring mass, they're measuring weight.

    The only 'mysticism' associated with this apparent conundrum relies on the reader not understanding the difference between mass and weight. Which no offence cisamcgu but you obviously don't.[/QUOTE]


    No it doesn't. You misunderstand. As Patrick said, under certain conditions the flying bird would exert force on the bottom of the box.
     
  15. Cycling Naturalist

    Cycling Naturalist Legendary Member

    Location:
    Llangollen
    The scales aren't measuring mass, they're measuring weight.

    The only 'mysticism' associated with this apparent conundrum relies on the reader not understanding the difference between mass and weight. Which no offence cisamcgu but you obviously don't.[/QUOTE]


    No it doesn't. You misunderstand. As Patrick said, under certain conditions the flying bird would exert force on the bottom of the box.[/QUOTE]

    Think of a hummingbird which also exerts a direct downforce.