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How Does A Ship Float on A Glass Of Water

  1. Jun 7, 2013 #1
    1. The problem statement, all variables and given/known data

    How Does A Ship Float on A Glass Of Water other than that he didnt gave me any details or it is really possible for a ship float in a glass of water in concept of density and buoyancy it's just our first week in class and i dont really have any idea

  2. jcsd
  3. Jun 7, 2013 #2
    Does "glass of water" mean the water and the glass, or just the water?
    If the later, then you can design the "glass" or container any way you want.
  4. Jun 7, 2013 #3


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    This was beat to DEATH here quite some time back in a long thread. Try a forum search.

    I started out vehemently opposing the idea but ended up seeing how it DOES work.
  5. Jun 7, 2013 #4


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    It's not a glass of water but a very small amount of water. Imagine a ship in a container that's the same shape as the hull of the ship and just barely bigger, perhaps just a few mm gap between the ship and the container, with water filling that gap. Since pressure within the water is a function of depth and not the quantity of water, and since buoyancy is a function of what would be the water displaced by the hull below the water line, it doesn't matter if that displaced water no longer exists within the container (otherwise the water wouldn't be "displaced"). (The ship could have been lowered into the container, spilling the displaced water outside of the container). So it doesn't matter that there is a small amount of water left in the container, and the ship will float on that thin layer of water. This only works if the density of the ship is less than the density of water.

    wiki article on bouyancy:

    Last edited: Jun 7, 2013
  6. Jun 7, 2013 #5


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    Some heavy rotating objects such as the lens systems in a light house float on a thin layer of mercury.

    You can see the round "tub" and the steel "boat" that the lens system floats on in this photo...


    Note the small gap for the "glass" of mercury.
  7. Jun 7, 2013 #6


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  8. Jun 7, 2013 #7


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  9. Jun 8, 2013 #8
    Hi Rittzlle,
    I am sure the thread above has answered all of you questions, I just wanted to add that the book recomended in the thread "thinking Physics" by L. Epstein is an excellent book and in it he states that this question was his fathers's favourite physics question.

    It is effectively what is happening in a dry dock once they seal the doors just before they pump the water out.

    Get the book
    Last edited by a moderator: Sep 25, 2014
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