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Force/density difference in liquid question

  1. Aug 5, 2008 #1

    lys

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    Hello,
    I am wondering how one can calculate the upwards force of a less dense object within a denser liquid based on the object's volume (or mass) and density, i.e of an air balloon in water.

    I've already searched for an answer for a while, but just don't seem to be asking google the right questions.
     
  2. jcsd
  3. Aug 5, 2008 #2

    Doc Al

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    Staff: Mentor

    Look up buoyancy and Archimedes's principle. Try: Buoyancy
     
  4. Aug 5, 2008 #3

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    Start with Archimedes's principle: an object submerged in water (or other liquid or gas) displaces its own volume. The upward force (bouyant force is, I think, the technical term) is just the weight of the fluid displaced minus the weight of the object. Since weight= mg, that would be g(massfluid- massobject). Since, further, mass is just density time volume, the force is gV(densityfluid- densityobject), where V is the volume of the object.
     
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