small error (I think)

Discussion in 'Feedback and Suggestions' started by Unregistered, Aug 20, 2007.

  1. Unregistered

    Thread Starter Guest

    To Whom It May Concern:

    I'm no scientist, which is exactly why I'm poring through this Web site. But facts are facts, I suppose...

    I believe that there is an error in the first section of volume II, where you begin to explain how we measure electrical units. You compare it to measuring mass and termperature.

    When you refer to measuring mass, you write, "For mass we might use the units of 'pound' or 'gram.'"

    I could be wrong, but I thought pounds were only used to measure weight -- that's to say the measurement of gravity's effect on an object (objects weighing differently on the moon, for example, than on Earth). Mass I had always understood as an absolute, to be measured only in grams, and only on a balance.

    Am I wrong? Can mass, indeed, be measured in pounds?

    Just curious. Thanks for the great site.

    Austin
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    No, the proper unit is the slug. Whose mass is such that it weighs 32 pounds @ 1G acceleration. As long as mass is defined as an absolute, the units do not matter. Just a meters/second is a valid measure of speed, so is furlongs/fortnight.
     
  3. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
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    Although technically incorrect, mass and weight are used interchangeably when they have a constant active medium, i.e. gravity, due to a relationship of direct proportionality in such circumstances. The distinction is only really relevant when considering objects in different gravitational fields.

    That said the pound is the unit if mass in the imperial measurement system: http://en.wikipedia.org/wiki/Pound_(mass)

    Can you provide a link to section in the e-book so I can look at it in context?

    Dave
     
  4. recca02

    Senior Member

    Apr 2, 2007
    1,211
    0
    does this help (i found this on wiki)
    and even if it was meant to measure weight as long as g remains same we really do not need to bother.
    even in engg applications pressures r referred in Kg/sq(cm) where g is missing.
    yet the unit is widely acceptable.
     
  5. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
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    Its bad news when we are using legislation drafted by politicians to validate an argument!! :D

    I suppose the question here is, is the pound a derived unit of measurement? If not, then it can without question be used as a unit of mass.

    Dave
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    Some time ago, a bill was intorduces into the Alabama legislature to change the value of pi to 3.000 so it would agree with a biblical reference.
     
  7. Dave

    Retired Moderator

    Nov 17, 2003
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    LMAO! Is that true?! See how in the crazy modern world I can believe such stories...!

    Dave
     
  8. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    When speaking of any unit of measurement I prefer one that has some immutable constant. Mass never changes regardless of gravity. Weight changes because of gravity. Definitions can vary though.

    When speaking of weight there are places you'd really want your gold weighed at. ;) Say on a neutron star but the banker would want one of the trojan points or deep space.

    http://en.wikipedia.org/wiki/Mass
     
  9. Dcrunkilton

    E-book Co-ordinator

    Jul 31, 2004
    416
    11
    I have changed the instance of pound to kilogram in the master copy at ibiblio. This should remove the mass vs force (weight) confusion factor.

    Thanks for the suggestion Austin. I have listed you as Austin@allaboutcircuits.com on the Contributors list. If you want to be listed under your real name please contact my by clicking above left on my name.
     
  10. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    144
    Good call Dennis. I think standardising the units used throughout the e-book are best, and we use SI units thus removing any ambiguity and bringing the e-book into line with other standard texts on the subject.

    Dave
     
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