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Archimedes Principle & Specific Gravity

  1. Nov 19, 2008 #1
    I was reading a lab online and I came across one that dealt with Specific Gravity and Buoyany and stuff.. and then they had these equations:

    *Note: p = density, M = mass, V = Volume, g = gravitational acceleration, W = Weight
    Subscripts: S = substance, W = water

    SG = pS / sW = (MS / VS) / (MW / VW) = (MSg / VS) / (MWg / VW) = (WS / VS) / (WW / VW)


    SG = (WS / V) / (WW / V) = WS / WW = WS / (buoyant force) = WS / (loss of weight in water)
    = WS / (WS - weight of substance in water)

    which all makes sense to me, mathmatically.. but then i thought about this part "WS / (buoyant force)" and that kinda throws me off because isnt Archimede's Principle that weight of an object is equal to the buoyant force.. and that makes SG always 1? but im pretty sure thats not the case, though..

    well, idk, im sure all you smart people will see something that i dont, lol. :tongue:
  2. jcsd
  3. Nov 19, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    No, it's not. Archimedes' principle states that the buoyant force equals the weight of the displaced fluid, not the weight of the object. Read all about it: http://hyperphysics.phy-astr.gsu.edu/Hbase/pbuoy.html#arch3"
    Last edited by a moderator: Apr 23, 2017
  4. Nov 19, 2008 #3
    oh, okay, lol.

    thanks :D
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