this post was submitted on 07 Oct 2023

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752

Fahrenheit vs. Celsius vs. Kelvin (i.imgur.com)

submitted 9 months ago by [email protected] to c/[email protected]

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[–] [email protected] 101 points 9 months ago (3 children)

Fun fact time, -40F is -40C.

And 575F is 575K

[–] [email protected] 73 points 9 months ago (19 children)

Fahrenheit is a strange scale.

[–] [email protected] 20 points 9 months ago

It's just designed with a slightly different set of assumptions.

Instead of water freezing and boiling 100° apart, it's 180° in fahrenheit. That makes it so that they're on the opposite sides of a temperature gauge, and a degree of rotation of the gauge matches a degree of temperature.
Instead of zero being the freezing point of water under specific conditions, it's a brine solution whose temperature will stabilize in a way that's useful for using as a calibration point.

Stripped of its context, it's odd. But it's not irrational, just no longer consensus as the standard, and as such deprecated.

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[–] mathterdark 76 points 9 months ago (6 children)

Fahrenheit: how hot humans feel

Celsius: how hot water feels

Kelvin & Rankine: how hot atoms feel

[–] [email protected] 45 points 9 months ago (14 children)

I don’t think how hot humans feel works at all, it’s just arbitrary

Can humans survive 100 degree heat? Yes so it doesn’t represent 100%

150 for 3rd degree burns (almost instant), does Fahrenheit go off base 150? Also no

What about cold? Well -40 requires a lot of layers, so then +40 should be pretty hot for humans right? Nope, because it’s not related to humans at all

[–] ThatWeirdGuy1001 25 points 9 months ago (1 children)

100°F was supposed to be average human body temp. Guy who made the scale fucked up his math and we ended up actually at 98.6°F

[–] [email protected] 12 points 9 months ago (2 children)

Nah, that's a myth. It's actually a little more complicated than that, and the actual measurements changed over time.

https://en.m.wikipedia.org/wiki/Fahrenheit

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[–] Espi 12 points 9 months ago (2 children)

If farenheit represents how humans feel then 50 is the most comfortable temperature right?

[–] [email protected] 7 points 9 months ago (1 children)

0 should be the most comfortable, with less being cold and more being hot.

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[–] [email protected] 70 points 9 months ago (3 children)

Based on human perception, based on water chemistry, based on physics.

[–] [email protected] 28 points 9 months ago (4 children)

You'll be shocked to learn that the distance in Kelvin is also adjusted to water "chemistry", albeit changing the aggregate state seems more physics to me, since no molceules are reacting with each other.

[–] [email protected] 10 points 9 months ago

Thankfully that has been redefined using the Boltzmann constant, so now anyone in the universe can agree on °C and K without needing to measure any Vienna standard ocean water.

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[–] [email protected] 10 points 9 months ago (1 children)

Zero Fahrenheit is the freezing point of brine (of a certain concentration). That's water chemistry.

Originally, 90F was based on the average human body temperature, but that later changed to 96F, which just goes to show how arbitrary that scale is.

[–] [email protected] 9 points 9 months ago (1 children)

It's all arbitrary. Someone just decided to base a scale off of something and that something isn't fixed from the start. The meter used to be based off the measurement of the earth, but now it's based off of light.

It's just some random semi-useful starting point that we all agree on so we're using the same language.

[–] [email protected] 7 points 9 months ago

The meter did not change, science has merely defined it more precisely and reliably over time. It is a measure of length, still one 40 millionth of the circumference of the earth through the poles. Other definitions like the speed of light definition will give you the same result. These newer definitions have reduced uncertainty and added ways to reproduce its length by natural means. But it's not like the 'original' meter was shorter or longer than today's meter, at least not by any noticeable margin.

Shifting the top end of a temperature scale by over five percent of the scale is a bit more arbitrary than that.

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[–] guriinii 57 points 9 months ago (13 children)

Since when is 0°C "fairly cold" it's literally freezing.

[–] [email protected] 46 points 9 months ago* (last edited 9 months ago) (4 children)

0°C is completely fine with jeans and a thick jacket, especially when it's sunny and there isn't much wind. It's cold, but there's probably not much ice or snow, if anything, probably mostly slush.

Compared to say -20 C where you should have a good ski jacket and ski pants, warm shoes and socks, generally multiple layers everywhere, winter gloves and so on.

[–] kamen 19 points 9 months ago (2 children)

It can be -20 C and you can be still fine with jeans and a jacket if it isn't windy.

What I'm saying is temperature alone doesn't tell you the whole story.

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[–] [email protected] 36 points 9 months ago

It is also literally melting.

[–] [email protected] 27 points 9 months ago (1 children)

I've been in -37C snow shoveling. Since then 0C doesn't even register as cold to me

[–] [email protected] 19 points 9 months ago (10 children)

Yep, and I've been in 110C in sauna. It's pretty fucking hot but not death

[–] obbelusk 10 points 9 months ago

I think more that if it's 100c outside the planet is basically dead.

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[–] kn33 16 points 9 months ago

The northern half of the US laughs

[–] [email protected] 6 points 9 months ago (2 children)

The temperature that water freezes at is only fairly cold weather by a lot of people's perception.
I'd call it "chilly". No jacket for running to the mailbox, or if I'll be outside for half an hour or so. Light jacket otherwise. I don't expect it to snow, since it's not actually cold enough usually, and there won't be ice on the ground unless it's just warmed up.

So it might be "freezing", but that doesn't make it cold.

[–] [email protected] 8 points 9 months ago (6 children)

It's almost like being 'fairly cold for humans' is a wide range, and subjective, therefore useless as a baseline.

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[–] EfreetSK 49 points 9 months ago (2 children)

I'd like to propose a discussion between a person from Arizona and a person from Alaska to define what is "Really hot outside"

[–] [email protected] 9 points 9 months ago (2 children)

Im from Texas, and 100F is "stay inside in the AC" weather. I bet an Arizonan would say the same.

[–] GraniteM 14 points 9 months ago

Being from a particularly hot or cold location doesn't make you immune to heat or cold, it makes you a connoisseur of heat and cold. You get better at recognizing gradations of extreme temperature (knowing which are uncomfortable and which can literally kill you if you're not careful), you learn how to plan ahead and dress for the weather, and you develop emotional coping systems for extremes.

But if it's either 100°F or 0°F, no matter where you're from, that's a temperature to be wary of.

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[–] [email protected] 8 points 9 months ago

Or cold

[–] JoeKrogan 49 points 9 months ago (28 children)

Celcius is the logical choice. The others are just crazy.

[–] nyoooom 45 points 9 months ago (1 children)

Kelvin and Celsius are the same, just offset onto absolute zero or the water freezing point

[–] [email protected] 18 points 9 months ago (1 children)

Yeah, often it is just way more convenient to use the Kelvin scale without any negative temperatures for some calculations and formulas then Celsius

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[–] neonred 31 points 9 months ago (2 children)

[–] WaxedWookie 15 points 9 months ago (5 children)

We should really normalise the Japanese system - it makes as much sense as the European system and has the benefit of being "alphabetically" sortable.