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Homework Help: I Need Help with Archimedes Priniciple and Bouyant Force

  1. Nov 1, 2006 #1
    How do you Determine whether it floats or not
    I know how to find the apparent force but how much force does it take to float above water and submergered but not sunken
  2. jcsd
  3. Nov 1, 2006 #2
    As per forum rules, please post your specific problem, your attempted work so far, and details of where/how you're struggling. We'll be happy to help you with that. :)
  4. Nov 1, 2006 #3
    Its not a specific problem but just in general i don't know how you can tell besides looking at it
    i'll find an example and post it i guess
  5. Nov 1, 2006 #4
  6. Nov 1, 2006 #5
    A cubic dm of aluminum is submerged in water. the density of aluminum is 2.70 X 10^3 kg/m^3

    F buoyant is 9.80 N
    F g is 26.5 N
    26.5-9.8= 16.7 N
    F apparent is 16.7 N

    how can you tell if it floats or not, i'm sure the answer is simple, but i'm not the brightest crayon in the box
    Last edited: Nov 1, 2006
  7. Nov 1, 2006 #6


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    Archimedes principle states that the buoyant force is equal to the weight of dsiplaced fluid. The maximum possible buoyant force is when the object is completely submerged. If the object has a volume V, then if it weighs less than the same volume V of fluid, it will float. If it weighs more than the same volume of fluid it will sink. If it weighs the same as an equal volume of fluid it is neutrally buoyant and will stay at any level it is placed in the fluid.

    The "apparent weight" calculation is the difference between weight and the maximum possible buoyant force. If that is positive, as it is in your example, the object will sink. If it is negative the object will float.

    When an object floats on a liquid, it only displaces the amount of liquid that weighs the same as the object. If it displaces more than that (because it was dropped in the fluid or is pushed down) it will bob up and down until the final level is reached.

    You can tell if an object will float by comparing its density to the density of the fluid. If an object is more dense than the fluid, then it will weigh more than an equal volume of fluid and it will sink. If it is less dense, it will float.
  8. Nov 2, 2006 #7
    thanks that makes much more sense than my book
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