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I Why does Celsius temperature in degrees have +/- signs, since it's scalar?

  1. Feb 10, 2019 #1
    Why does Celsius degrees have +/- signs, since it's scalar?
     
  2. jcsd
  3. Feb 10, 2019 #2

    phinds

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    How would you recommend temperatures below zero Celsius be indicated?
     
  4. Feb 10, 2019 #3

    Dale

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    Scalars can be negative. You are thinking of a magnitude which is strictly non-negative. Temperature is not a magnitude.
     
  5. Feb 10, 2019 #4
    Thank you so much for the distinction. That makes perfect sense.
     
  6. Feb 11, 2019 #5

    sophiecentaur

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    The Celcius scale (also the Fahrenheit scale) uses values that relate to arbitrary points on an absolute temperature scale. That scale starts at Zero K so all temperature values are actually 'in the same direction'.
     
  7. Feb 11, 2019 #6
    Yea, the Kelvin scale makes more intuitive sense to me, but yea the arbitrary nature of that zero point makes sense too, as representing another temperature scale. Thank you!
     
  8. Feb 11, 2019 #7

    boneh3ad

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    It's not really arbitrary, though. The scale for Celsius was chosen so that 0 was the freezing point and 100 the boiling point of water, two commonly-occurring phenomena in everyday life. Similarly, Fahrenheit's scale was chosen to relate to a human's every day experience. Absolute scales like Kelvin or Rankine are non-negative, which is nice, but they are much harder to intuitively relate to what you experience in life. It's a lot less convenient to talk about freezing occurring at 273.14 K and boiling at 373.14 K.
     
  9. Feb 11, 2019 #8

    Vanadium 50

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    Originally, the reverse. It was changed by Linnaeus (yes, that Linnaeus) after Celsius' death.
     
  10. Feb 11, 2019 #9
    Yes, but in the big picture it is arbitrary -- we could be doing our labs on the planet Zork, where atmospheric pressure is different.

    Where I live, water boils at 204F. Oops, I mean 95.6 Celsius.
     
  11. Feb 11, 2019 #10

    boneh3ad

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    Still not arbitrary. It has a specific and logical reason.
     
  12. Feb 11, 2019 #11
    It has a specific and logical reason, but it is arbitrary.
    Lots of other values could have been used for equally
    specific and logical reasons.

    -- Jeff, in Minneapolis
     
  13. Feb 12, 2019 #12

    LURCH

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    You mean 0° used to be the boiling point of water, and 100° was the freezing point? Well then I’m glad it got changed; that’s just confusing.
     
  14. Feb 12, 2019 #13

    A.T.

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    If the Celsius scale is "arbitrary", then so is the Kelvin scale. The difference of 1K is still based on boiling and freezing of water.
     
  15. Feb 12, 2019 #14

    boneh3ad

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    ar·bi·trar·y
    /ˈärbəˌtrerē/
    adjective
    1. based on random choice or personal whim, rather than any reason or system.

    So... not arbitrary.
     
  16. Feb 12, 2019 #15

    A.T.

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    Except for arbitrary definitions of "arbitrary".
     
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