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Fred_Kohlhepp23-Emerald I
23-Emerald I
September 3, 2015
Solved

Trouble with temperature

  • September 3, 2015
  • 2 replies
  • 4648 views

I've always had issues with temperature units, early Mathcad had "R" and "K," for Rankine and Kelvin; these made sense, they were confusing but it was the confusion we had been dealing with since we learned about "hot" and "cold."

Then we were given the Centigrade and Fahrenheit scales, and if that didn't suffice, the "difference in temperature" scales.

I began the attached sheet to calculate the change in size as a function of temperature change.  I got my answer, but I also got an aggravating question.

Can anyone explain the attached (version 15) sheet; how can -321 °F not be -321 °F?

Best answer by LucMeekes

Because there's a difference between:

If you know that °F is a function and -321 is (or, appears to be) the parameter it is applied to.

You cannot see it, not even in the mathcad sheet itself, but in fact the first expression is °F applied to -321, while the second expression is the negative of °F applied to 321. To make it explicit:

Success!
Luc

Here's one of the causes for trouble with temperature units:

If today the out-door temperature is 32 °F, and tomorrow it will be twice as cold, then what will the out-door temperature tomorrow be?

2 replies

L
LucMeekes23-Emerald IVAnswer
23-Emerald IV
September 3, 2015

Because there's a difference between:

If you know that °F is a function and -321 is (or, appears to be) the parameter it is applied to.

You cannot see it, not even in the mathcad sheet itself, but in fact the first expression is °F applied to -321, while the second expression is the negative of °F applied to 321. To make it explicit:

Success!
Luc

Here's one of the causes for trouble with temperature units:

If today the out-door temperature is 32 °F, and tomorrow it will be twice as cold, then what will the out-door temperature tomorrow be?

R
RichardJ19-Tanzanite
19-Tanzanite
September 3, 2015

Is a physicist asking, or an engineer?

L
LucMeekes23-Emerald IV
23-Emerald IV
September 3, 2015

This is one question of a list of questions to ask your teacher in school.

V
24-Ruby IV
ValeryOchkov24-Ruby IV
24-Ruby IV
September 4, 2015

It is one old story:

Re: Ward No. 14: Negative absolute temperature

L
LucMeekes23-Emerald IV
23-Emerald IV
September 4, 2015

You're right Valery.

In Prime 3.1 (and I guess/hope the same is/will be true for earlier and newer versions of prime) you cannot apply the minus sign to the entire expression without ending up with brackets:

And if you remove a bracket in the second expression, (the other bracket also automatically disappears as it should and) the minus sign gets applied to the number alone, so you end up with a copy of the first expression and (therefore) the result changes to 77.039 K.

V
24-Ruby IV
ValeryOchkov24-Ruby IV
24-Ruby IV
September 4, 2015

Two useful cloud functions for the working with temperature:

tt.png

And the second.

Maple has 6 temperature scales, but Mathcad only 4. why?

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