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Lbm or lbf?

  1. Sep 29, 2014 #1
    I'm sure this has been asked before but it's annoying me. When we weigh ourselves is it in lbm or lbf?

    Because we weigh different on say, the moon, our weight must be lbf right? But if I weigh 150 any unit converter will say I weigh 68kg. Or do I weigh 2.13kg? Can I say I weigh 21 Newtons?
    [tex]\frac{150lbf}{32ft/s^2}*\frac{1lbm}{2.2kg}\cong2.13kg*9.8m/s^2\cong21N[/tex]
     
  2. jcsd
  3. Sep 29, 2014 #2

    CWatters

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    Domestic scales measure the force you apply to them so it would be reasonable for them to display the result in Newtons but they all assume they will be used on earth and have scales calibrated in kg (or some imperial equivalent). In effect they attempt to display your mass. Since gravity isn't the same everywhere on earth they won't display the correct mass everywhere.
     
  4. Sep 29, 2014 #3

    sophiecentaur

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    This is an old chestnut. Essentially, Weight is the force which pulls you down and it can vary with position. One really has to come to terms with the common usage of the term 'Weight' and use the context of any statement to decide what is really meant. You can waste far too much time trying to reconcile the two worlds of Science and everyday life. There is a danger of getting a name for nerdiness if you inflict strict definitions on innocent people in civvy street.
     
  5. Sep 29, 2014 #4
    Weight is measured in pound-force. Mass is measured in pounds, (or pound mass?). But the term "weigh" can mean many things in the English language, including general measurement. Example: "weigh a decision"
     
  6. Sep 29, 2014 #5

    sophiecentaur

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    This certainly is a weighty subject.
     
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