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Very basic question.

  1. May 22, 2003 #1
    First I want to say that some of these discussions are way over my head but others I find very interesting and I will continue to read through the threads just to exspand my understanding. I have tried a few searches and not found exacly what I am looking for so here it is.
    I want to figure out what it will take to float myself in water.
    My weight is 160 lbs and my understanding is that water is 62 lb per cubic foot for its weight. So to me that means 160/62= the amount of water I need to diplace to float myself or or 2.58 cubic feet of water needs to be diplaced. Is that correct?
     
  2. jcsd
  3. May 22, 2003 #2
    Uhm, float yourself? I think most people float on top of water normally, I sure do.

    I go in the pool and lay down and I float on top, no problem at all. So I'm confused...
     
  4. May 22, 2003 #3

    chroot

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    Yep. You'll need to displace at least 2.58 ft3 of water to float.

    - Warren
     
  5. May 22, 2003 #4
    I'm thinking that the density of your body needs to be factored into the equation. If you have a lot of 'blubber' you will be more buoyant than a lean person of equal weight with a higher level of muscularity.

    [edit]
    On the other hand, I'm thinking more along the lines of scuba diving, were a 'fattish' person will require more lead weights on his/her belt.
     
    Last edited by a moderator: May 22, 2003
  6. May 22, 2003 #5

    chroot

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    What else do you think weight and volume would be used to determine? The statement a 162 lb man must displace more than 2.58 ft3 of water to float is equivalent to the statement the man must be less dense than water to float.

    - Warren
     
  7. May 22, 2003 #6
    I think I confused myself.

    I was thinking not of displacement, but how some people are more buoyant than others...
    Does that make any sense? I’m confused…
     
  8. May 22, 2003 #7

    chroot

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    Re: I think I confused myself.

    Fat percentage and lung volume are the two largest variables.

    - Warren
     
  9. May 22, 2003 #8

    ahrkron

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    I think this is correct (I have no idea about the numbers though).

    The relation betwenn this and density is that the ammount of water you displace is related to your volume.

    Sometimes exagerating things help understanding. For instance, imagine you weight 160 lbs, and that you are extremely big, so that your legs already have a VOLUME of 2.58 cubic feet. This means that once you have submerged them, you already pushed away all the water you needed in order to float.

    On the other hand, if you weight the same 160, but your whole body only occupies 2 cubic feet, then even if you sink completely you won't displace enough water to have a buoyant force equal to your weight.

    Does that help?
     
  10. May 22, 2003 #9
    It helps me clear out a few cobwebs from out of my head. Thanks!!
     
  11. May 22, 2003 #10
    follow up

    Im sorry I should of been more specific. I was trying to keep it simple and instead made it more difficult. By float myself in water I should of said float myself in a boat. In the example I should of said myself and the boat weight would be 160 lbs.
     
  12. May 22, 2003 #11

    chroot

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    The same discussion applies.

    - Warren
     
  13. May 23, 2003 #12
    eureka!
    ok all kidding aside, you can use Archimedes principle here with no problem whotseuever.
    ρ-naught/ρ-fluid = Volumme-fluid/Volume-naught
    Also, since you're not accelerating when you're floating, the sum of the forces = ma = 0, so Bouancy force = mg = ρVolume
     
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