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Could use help before Sunday the 15th

  1. Apr 13, 2007 #1
    I've convinced a local pool to let me do a pressure check on an invention that I'm working on, Sunday the 15th, but I've only got about 15 or twenty minutes to get it tested.
    What I need to do is to weight down approximately a gallon container of air down to a depth of 12 feet, and to do this I've got two 15 pound weights from a barbell.
    The question is, can I get this container down that far by just useing one of the weights?
  2. jcsd
  3. Apr 13, 2007 #2
    How's this an invention? What purpose does this serve?
  4. Apr 13, 2007 #3
    I'm working on a new alternative energy principle, it's part of the system, although, not to spec, but it will give me I hope three answers.
  5. Apr 13, 2007 #4
    I think that the force of buoyancy = (mass of fluid displaced) - (mass of object).

    In this case, air has a density of 1.2kg/m^3. 1 gallon = .00379 cubic meters. 1.2kg/m^3*.00379m^3 = .00454 kg, which equals .0100lbs. So, 1 gallon of air equals .0100 pounds.

    one gallon = .00379 cubic meters

    well you are essentially pushing up one gallon of water. this weighs:

    one gallon of water has a weight of .998g/cm^3 =998kg/m^3:: 998kg/m^3*.00379m^3 = 3.78kg::<b>8.33lbs.</b>

    your weights weigh 15 pounds, but also have boyancy.

    water has a density of 8.33 lbs/gallon.Assuming your weights have a volume of less than 2/3 of a gallon, you should be fine (2/3 of a gallon weighs about 5.6 lbs. your weight weighs about 9.4 lbs more, so that should overcome the 8.33lbs of buoyancy of the gallon of water). if they have a volume of 1 gallon, you will need both weights.

    i hope that makes sense...
  6. Apr 13, 2007 #5


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    Staff: Mentor

    You're working on an alternate energy invention involving buoyancy and you don't know how to calculate buoyancy? :surprised
  7. Apr 13, 2007 #6
    my knowledge at this time is the principle of the working parts of the application in that it's what I have worked on, and I have gone through its machinations, this part of the test is only by degree.
    But since I only have a little time to test it, I don't want to secure another weight that will not ad to the understanding of what I'm looking for, but just ad more weight I would need to lift when the test is over.
    Once I do my test, hopefully I will be correct in my ingenuity.
    PS, by the way the container of air will have other pieces connected, I didn't mention this, because I was only looking for the one answer so far.
    Last edited: Apr 14, 2007
  8. Apr 15, 2007 #7
    Had my test, and didn't concieve one problem, I don't weigh much, and since I didn't take a weight belt to keep me down underwater, it was a nightmare just trying to stay underwater at a depth of five foot.
    But I did test it at this depth briefly, it made me realize that I need to make my prototype device larger, and as far as my allotted fifteen minutes, it has now been extended to any Sunday, they evidently liked the premise?
    Last edited: Apr 15, 2007
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