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Homework Help: Pound Force and Pound Mass

  1. Feb 27, 2008 #1
    This is the most refined concept I could make by reading wikipedia. Our thermodynamics' teacher today introduced us to the 'real' English Engineering system.

    My confusion was that like we know if we want to find the weight of a 51 kg person we would simply multiply it with 10(approx) and get 510 N.If we have 51 lbm and want to convert it into lbf then we can't simply multiply it with 32.2(approx) and get the answer but we will also have to take that 'g subscript c' into account which is also 32.2 and so these two 32.2s cancel out and we get 51lbf.

    Am I right?
  2. jcsd
  3. Feb 27, 2008 #2


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    Science Advisor

    You are correct. Just remember in the English system, the direct correlation to the kg is NOT the Lbm. It is the slug. In that case you don't have to worry about Gc.

    Take a look here and notice the table at the top of the article.
    http://en.wikipedia.org/wiki/Slug_(mass [Broken])
    Last edited by a moderator: May 3, 2017
  4. Feb 27, 2008 #3
    Thanks a lot.
  5. Feb 28, 2008 #4


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    There are actually two "British systems".
    1. A body with a mass of 1 slug weighs 32 pounds.
    2. A body with a mass of 1 pound weighs 32 poundals.
    Of course, you have to stick with one or the other throughout a calculation.
    So "pound" can mean either "mass" or "force", depending on the system.
    One of these systems (I think the poundal) was called the "engineering" system.
    In any event, colloquially, if an American "weighs" 220 pounds, his European twin
    "weighs" 100 kilo, even if some terms are used incorrectly.
  6. Feb 28, 2008 #5
    Got it. Thanks
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