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Archimedes Principle

  1. Sep 25, 2004 #1
    How would I best explain Archimedes Principle to kids 9-10? So they can understand it? I don't need any experiments, All I want is an easy explination on what it is and how it works so 10 year old kids can understand. And in the shortest amount of words.....
  2. jcsd
  3. Sep 25, 2004 #2


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    For stuff that floats, the water displaced (think of a full bathtub) has to weigh the same as the floating object, since the remaining water is carrying the same load.

    For stuff that sinks, it is a volume displacement.
  4. Sep 25, 2004 #3


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    How about this:
    1.Think of a portion somewhere in the fluid (we assume the fluid is at rest).
    2.That portion isn't moving, in particular, it isn't falling down.
    3.So, another force than the weight of the fluid portion works on it to keep it from falling down (that's called the buoyancy force)
    4. Now, what's making that force?
    Answer: The rest of the fluid surrounding your portion (i.e, through the fluid pressure)
    (What else could it be?)
    5. Suppose you switched out your selected portion with an object of the same shape and volume.
    The water surrounding that object can't see the difference between that object and your original fluid portion (why should it?)
    But that means that the surrounding fluid gives the same buoyancy force onto the object as it did on the displaced fluid.
    (That is, Archimedes law)

    Is this too difficult?
    (This explanation is called Stevin's principle, after a Dutch scientist Simon Stevin in the 17th century)
    Welcome to PF, by the way.
  5. Sep 25, 2004 #4
    Thanks! Can anyone provide some sort of cartoon? I want to provide a visual, but I don't have the time to do an experiment.
    Sorry if I am being difficult....
  6. Sep 27, 2004 #5
    easiest and practicle way

    The most easiest and practicle way is, take a little heavy book a put it on his head. He will obveously try to lift it with his hands or by straightening his neck, explain to him that like he do not want weight over him similerly fluids do not want any mass over them hence the exert upward foce on them.
    I Think it will work.
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