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Thread: Density and Floating Question

  1. #1 Density and Floating Question 
    Forum Freshman AlphaParticle's Avatar
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    Oct 2010
    I recently heard on a television program (mythbusters to those who may know it) and heard that you float on water becuase you are less dense that it! Unfourtanetly immediately after i thought, "Hold on, why would being less dense make you float?". And now here i am asking...Why does being less dense than water make you float? (when answering remember i'm 14!!!)

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  3. #2  
    Forum Freshman
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    Apr 2011
    This link will give you an excellent answer on a level you should be able to comprehend.
    Ask a scientist - Floating

    the short version:
    When you put something (say a boat) on the water, it 'bends' the shape of the surface of the water. Water in a pond without wind is nice and flat. a boat however seems to be partially in the water and partially floating. In fact the boat is simply pushing the water below itself away.
    The water however will 'resist' being pushed away.

    So on one side (let's call it the top) there is a boat pushing down. On the bottom there is water pushing the boat upwards. The downward force by the boat is dependant on it's mass. If the water resists harder than the object wants to sink, it will stay afloat. If not, it will sink.

    The upward force from the water is based on the 'volume being affected' by the boat.

    The balance that describes this relationship (mass per volume) is called density. The higher the density, the more weight will be pressing down per volume.

    Iron for example has a density of 7.8kg/dm≥. Water has a value of 1 kg/dm≥.
    if iron is on top it will push down harder than water will 'push up'. vice versa the water cannot press down hard enough for the iron to move. thus water will not sink into iron (assuming the iron is liquid).

    ps: I know I've been loose with some terms like sinking and forces but I'm trying to explain it in Leyman's terms. Don't hold it against me.

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  4. #3  
    Veracity Vigilante inow's Avatar
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    Oct 2009
    Austin, TX
    The concept of buoyancy is useful here, too. Look into some explanations of that like on wiki and that might help.
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  5. #4  
    Iuvenis ducis Darkhorse's Avatar
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    Mar 2011
    Just to give you something else to chew on. All water is not equally dense. Extremely salty water like the dead sea is much more dense that regular sea water or fresh water so objects that are put in it float much easier.
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