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Grab a bag of sugar and say this weighs 1KG

  1. Sep 24, 2009 #1
    If I were to grab a bag of sugar and say this weighs 1KG. What do I actually mean?

    KG is the unit for mass, not weight. What is the actual weight of the bag of sugar? (Assuming I'm on earth) Would it be 9.81N?

    This has been running through my mind recently, I want to try and put the common world into it's proper perspective.
     
  2. jcsd
  3. Sep 24, 2009 #2
    Re: Weight

    You are right mass and weight are different things and on earth every Kg weighs 9.81N.
     
  4. Sep 24, 2009 #3

    D H

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    Re: Weight

    There are not different things colloquially, and more importantly, they are not different things legally. You have to be careful here. Weight has multiple meanings. A synonym for mass is one of them.

    And that is simply not true. A kilogram has a scale weight of 9.779 newtons in Mexico City but 9.819 newtons in Oslo. That is exactly why legally weight is a synonym for mass.
     
  5. Sep 24, 2009 #4
    Re: Weight

    So when a "common" person refers to weight they actually mean mass and it's the word that's incorrectly used, not the unit?
     
  6. Sep 24, 2009 #5
    Re: Weight

    Well when people say weight in kilos, they are using the unit of mass.

    However! You can describe weight as "kilograms force". Which is descirbing the weight that 1 kilogram of mass would make in standard gravity.

    1 KgF = 9.81 N = 1kg mass * gravity



    Its only the same as imperial units. Lbs for mass and lbf for force.

    1 lbf is the force given by a 1 lb weight * gravity.
     
  7. Sep 24, 2009 #6

    D H

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    Re: Weight

    The word is fine. Many words have multiple meanings. Suppose you pick an argument with a lay person regarding their supposed incorrect use of the the word "weight". One of the two of you is indeed wrong: You.
     
  8. Sep 24, 2009 #7
    Re: Weight

    But it is scientifically wrong, isn't it?
     
  9. Sep 24, 2009 #8

    D H

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    Re: Weight

    My personal opinion: In this case it is the scientists that are wrong. Look at it this way: Scientists really, really do not like the way the lay community has contorted the meaning of the word "theory". A scientific theory is the gold standard of science. You can't get any better. Somehow, theory has been contorted to mean "wild-assed guess" in the lay community -- and the lay community uses this meaning to question science. For example, "Evolution is only a theory, isn't it?"

    If we want to get uppity about the lay community usurping our terms, we ought not to usurp theirs. If we do, we ought not to get uppity about the lay community continuing to use their terms in the way they have used them for a long, long time.
     
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