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Will a Blow Up Doll filled with Helium Float?

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    This is a prank me and my friends want to pull off. I want to work out whether its feasible using buoyancy, but I have no idea what to use as the mass of the doll and the volume. Any ideas?
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    Prank with you and your friends....sure.
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    I wouldn't have thought so, the material used to make them is much heavier than a balloon.
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    Well the weight of the doll multiplied by gravity is the force acting downwards. So say it 0.5kg heavy, its force downwards would be the mass, 0.5, timsed by the force of gravity (9.8 in Mechanics or 9.81 in Physics) which gives a downward force of 4.9N, I think.
    I'm not sure how you'd find the upward force considering it's helium, look on the internet for some research.

    Hopefully, this has been some sort of help.
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    No harm in trying. After all, you've probably got spares lying around, eh?
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    Someone clearly missed Myth Busters this evening.
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    (Original post by multiplexing-gamer)
    Well the weight of the doll multiplied by gravity is the force acting downwards. So say it 0.5kg heavy, its force downwards would be the mass, 0.5, timsed by the force of gravity (9.8 in Mechanics or 9.81 in Physics) which gives a downward force of 4.9N, I think.
    I'm not sure how you'd find the upward force considering it's helium, look on the internet for some research.

    Hopefully, this has been some sort of help.
    Downward force is easy, dont worry i'm taking physics. you also need the weight of the helium.
    Upward force is called buoyancy, for which i need the volume... any ideas?
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    depends... (my opinion)
    the total mass of the helium and material has to be less than the air of the same volume

    (Original post by multiplexing-gamer)
    the force of gravity (9.8 in Mechanics or 9.81 in Physics)
    dont get too into this (which to use for which)... id rather use 9.8 as a general value... the field strength varies across the planet
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    Calm down with the sex gags. If i was doing a blow up doll, i wouldnt want it to be hard to get.
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    (Original post by Dmon1Unlimited)
    depends...

    the total mass of the helium and material has to be less than the air of the same volume
    I think so too. but my friends are doubtful. Apparently 'balloon' helium isn't pure, we are thinking about buying some industrial He to be sure.
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    Of course it will float; they all float.

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    So this is why they're calling physics a 'boys subject' nowadays. :holmes:
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    (Original post by juliusb)
    I think so too. but my friends are doubtful. Apparently 'balloon' helium isn't pure, we are thinking about buying some industrial He to be sure.
    if you can work out whether the entire system is lighter than its air equivalent volume, and its still less, then does it matter?

    be careful with it, wouldnt want it to ignite (or be breathed in too long)
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    (Original post by hollywoodbudgie)
    So this is why they're calling physics a 'boys subject' nowadays. :holmes:
    me and some mates designed a rocket and launched it in the park...

    it was the crappiest launch ive ever witnessed, but it was funny as hell...


    warning: dont try this at home kids (or anywhere) :pierre:
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    (Original post by Dmon1Unlimited)
    if you can work out whether the entire system is lighter than its air equivalent volume, and its still less, then does it matter?

    be careful with it, wouldnt want it to ignite (or be breathed in too long)
    Guess you don't do Chem. Helium won't ignite however hard you try.
    The breathing is dangerous you are right.

    But yeh this is my question, is the entire system lighter than its equivalent air volume?
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    (Original post by juliusb)
    Downward force is easy, dont worry i'm taking physics. you also need the weight of the helium.
    Upward force is called buoyancy, for which i need the volume... any ideas?
    fill it up with air and measure the displacement of water from a bath. Easy way would be to fill up the bath, mark a level on the side, then submerge the thing, which will raise the water level and then remove the water to get it back to it's original level. I doubt it'll have enough volume though.
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    Pretty unlikely as they're made of fairly thick plastic to take the strain of *ahem* their intended use. also Baloons are a pretty efficient shape for holding a volume with the least surface area, Therefore material and mass are minimised. Thats not really true for dolls which are a pretty inefficient shape imo.
    Suppose you could submerge the inflated doll in a bathtub then find the number of baloons you need to hold under to raise the level by the same amount. If that number of balloons weighs much more than your doll you're in trouble.
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    (Original post by Tobedotty)
    fill it up with air and measure the displacement of water from a bath. Easy way would be to fill up the bath, mark a level on the side, then submerge the thing, which will raise the water level and then remove the water to get it back to it's original level. I doubt it'll have enough volume though.
    That would work well, but we haven't bought the doll yet...
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    (Original post by Joinedup)
    Pretty unlikely as they're made of fairly thick plastic to take the strain of *ahem* their intended use. also Baloons are a pretty efficient shape for holding a volume with the least surface area, Therefore material and mass are minimised. Thats not really true for dolls which are a pretty inefficient shape imo.
    Suppose you could submerge the inflated doll in a bathtub then find the number of baloons you need to hold under to raise the level by the same amount. If that number of balloons weighs much more than your doll you're in trouble.
    You're right, you reckon if we tied on a few balloons it would make a difference? or would that be too many? I mean kids fly off with helium balloons all the time..
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    want the doll to go on top for once?

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