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hpr1432 :: Fahrenheit 212

A discussion of temperature systems: Fahrenheit, Celsius (Centigrade) and Kelvin

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Hosted by cyan on 2014-01-28 is flagged as Clean and is released under a CC-BY-SA license.
Science, temperature. 3.
The show is available on the Internet Archive at:

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Duration: 00:19:08


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Ken requests an episode on Fahrenheit, which really requires discussion of the two temperature systems, and how they are quantified.


Centigrade: old fashioned term for Celsius
Kelvin (K): less common measurement of temperature used for Science
Thermal Equilibrium:
Zeroth Law of Thermodynamics:
Absolute zero:

My personal preference is Celsius. Less numbers to deal with in everyday use.
Really Cold – Temperatures below 0°C
Really Hot – Temperatures above 30°C
The "American" thinking is temperatures go in 20's, 30's, 40's...etc. more work!
Obligatory gun discussion
Indirect conversation about PV = nRT formula
Correction: the absence of pressure (vacuum) causes water to boil.
Celsius and Fahrenheit are "measured" by the states of water boiling/freezing.

freezes at 0°
boils at 100°

freezes at 32
boils 212°

1 (K) Kelvin = -273.15°C


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Comment #1 posted on 2014-01-18 17:56:02 by Donald Desjardin

Mildly miffed comment

When the presenter of this show talked about how the Farenheight numbers were crazy/random/strange, I vaguely remembered from my early grade school days that there was a logical reason for the numbers.

So I tried to look up the reasons as I remmebered them, but couldn't find anything on the web.

From what I remember (almost 50 years ago) the person that developer the F scale (just like Mr Celcius) also wanted to use some known standards, and the coldest temp known and used was the freezing point of ocean water roughly zero F (it depend on the amount of salt/saturation in the water), and the 100 measurement was not the hottest point known (because they were still discovering hotter things), but the human body (98.6 is pretty close to 100, and i don't think they had the decimal precision then).

Hope that clear it up and makes un American's look a little less strange :-)



Comment #2 posted on 2014-01-21 17:38:58 by Ken Fallon

'twas I

Hi Don,

I'm the one that was ranting about the arbitrariness of the Farenheight scale. You are of course correct that the celcius scale is equally arbitrary, but at least there is a known reason for it. So I was thrilled to hear your explanation but my hopes were dashed by none other than the US Navy, "The freezing point of seawater is about 28.4°F (-2°C), instead of the 32°F (0°C) freezing point of ordinary water. "

But then wikipedia ( explains "The lowest temperature was achieved by preparing a frigorific mixture of ice, water, and ammonium chloride (a salt), and waiting for it to reach equilibrium. The thermometer then was placed into the mixture and the liquid in the thermometer allowed to descend to its lowest point. The thermometer's reading there was taken as 0 °F. "

Not that seems to support your point but then we have "The second reference point was selected as the reading of the thermometer when it was placed in still water when ice was just forming on the surface. This was assigned as 32 °F. " - Which begs my question why pick 32 degrees for that ?

Continuing "The third calibration point, taken as 96 °F, was selected as the thermometer's reading when the instrument was placed under the arm or in the mouth." So he may have been using a multiple of 32 but why ?

Also - you owe me a show :)


Comment #3 posted on 2014-01-26 07:49:54 by Ken Fallon

5150 make a complying argument for Fahrenheit

0 Fahrenheit - Really cold outside 100 Fahrenheit - Really hot outside

0 Celsius Fairly cold outside 100 Celsius Dead

0 Kelvin Dead 100 Kelvin Dead

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