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Basic bouyancy

  1. Jan 1, 2008 #1
    1. The problem statement, all variables and given/known data

    I have a balloon with helium in it, I need to know the acceleration that it rises. It would be great if you could tell me what I need if I am missing any. This is what I have,

    Density of liquid(air) = 1 g/l
    Density of Helium = .1786 l/g
    Volume of Balloon = 91 cubic centimeters

    I need to know the velocity upwards as I change the Density of the Balloon

    2. Relevant equations



    3. The attempt at a solution

    I got the 91 cubic centimeters, also figured out .1786, other than that... horrible failure, like 1000 meters per second
     
  2. jcsd
  3. Jan 1, 2008 #2

    Doc Al

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    Staff: Mentor

    What forces act on the balloon? What's the net force?

    What's the mass of the balloon?

    Apply Newton's 2nd law.

    (You won't need the velocity of the balloon to find its acceleration.)
     
  4. Jan 1, 2008 #3
    to find the mass I need the weight, I don't have the physical balloon, how can I figure out using the percentage of helium as a variable how much it weighs? then I can multiply times 9.8 and get the mass? I think it was a mistake taking a.p physics, it is so tough for me
     
  5. Jan 1, 2008 #4

    Doc Al

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    Staff: Mentor

    You have the volume and the density, so you should be able to find the mass of the helium. (Ignore the mass of the balloon material itself--assume it's zero unless you are given it.)
     
  6. Jan 1, 2008 #5
    I found out a better way to ask the question. Do you know of a way to calculate acceleration as a function of density?
     
  7. Jan 1, 2008 #6

    Doc Al

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    Staff: Mentor

    You'd figure out the acceleration in the same manner that I described above.

    What information are you given?
     
  8. Jan 1, 2008 #7
    It's a science fair, I am see'ing the effect of helium on a balloon in air
     
  9. Jan 1, 2008 #8
    can I have an equation to find the mass of the helium? then using that, find acceleration
     
  10. Jan 1, 2008 #9

    Doc Al

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    Staff: Mentor

    What equation relates density to mass and volume? (What's the definition of density?)
     
  11. Jan 1, 2008 #10
    d = m/ v

    mass per unit if volume
     
  12. Jan 1, 2008 #11
    of volume*
     
  13. Jan 2, 2008 #12
    I got an A on my science fair checkup! thanks so much
     
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