## Kelvin vs. Celsius

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Capt.Awesome
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### Kelvin vs. Celsius

So, with 83+ pages of topics in "Science" I decided just to start a new topic for my question

I am an AP chemistry student and I came across a slight problem when converting between Kelvin and Celsius.
When you convert from Celsius to Kelvin you simply add 273.15 to the Celsius temperature. that part is easy. But when I tripple the number they should be the same.
i.e. if I take 6C and I tripple it I get 18C. When I convert 6C into Kelvin I get 279.15K. When I tripple 279.15K and convert back into Celsius (873K -273= 564C) I get 564C. These are obviously off a little bit.
Which is correct? What am I doing wrong, and why is it wrong?

Tass
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### Re: Kelvin vs. Celsius

Capt.Awesome wrote:So, with 83+ pages of topics in "Science" I decided just to start a new topic for my question

I am an AP chemistry student and I came across a slight problem when converting between Kelvin and Celsius.
When you convert from Celsius to Kelvin you simply add 273.15 to the Celsius temperature. that part is easy. But when I tripple the number they should be the same.
i.e. if I take 6C and I tripple it I get 18C. When I convert 6C into Kelvin I get 279.15K. When I tripple 279.15K and convert back into Celsius (873K -273= 564C) I get 564C. These are obviously off a little bit.
Which is correct? What am I doing wrong, and why is it wrong?

Why should you triple it? Multiplying a temperature only makes physical sense on the absolute (that is: Kelvin) scale. 2C is not "twice as hot" as 1C.

Also be careful when considering differences: The difference between 10C and 6C is 10C-6C=4C. I you do it in Kelvin you get 283K-279K=4K. Note the difference is the same in both scales. You can't convert back and say that the difference is 277K. (I've seen books do this, although with Celcius and Farenheit. No 2degreesC/m is not 36degreesF/m).

If your triple temperature goes in any sort of formula then it is safe to say that doing it on the Kelvin temperature is the right.

Gigano
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### Re: Kelvin vs. Celsius

The scale of Kelvin and Celcius are the same: the differ in what temperature they label with 0 degrees. Celcius sets 0 degrees to be the melting point of water, while Kelvins sets 0 degrees to be the absolute thermodynamic zero (-273.15 degrees C).

Thus when tripling a temperature in Celcius, and wanting to convert it to Kelvin, you should just triple the temperature in C, then add 273.15. So your tripling of 6 C and subsequent conversion to Kelvin would be (6 * 3) + 273.15 = 291.15 K.

And as Tass has pointed out, only factoring temperatures in the Kelvin scale actually mean that one temperature is a factor n hotter than another temperature (i.e. 500K is twice as hot as 250K; respectively 226.85 and -23.15 degrees C).
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yurell
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### Re: Kelvin vs. Celsius

For your chemistry uses, you'll likely be needing temperature in Kelvin before performing any maths on it.
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mfb
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### Re: Kelvin vs. Celsius

Tass wrote:Also be careful when considering differences: The difference between 10C and 6C is 10C-6C=4C. I you do it in Kelvin you get 283K-279K=4K.

Use Kelvin for temperature differences please, exactly for that reason. A difference of 4°C has no physical meaning, a difference of 4K has.

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### Re: Kelvin vs. Celsius

mfb wrote:A difference of 4°C has no physical meaning, a difference of 4K has.
A difference of 4 degrees C has exactly the same meaning as a difference of 4K, actually.
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BobTheElder
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### Re: Kelvin vs. Celsius

Surely the problem here is just the basic math?
multiplying a BIG number by amount x gives you a bigger increase than multiplying a SMALLER number by x.
Surely this just means you shouldn't be doing multiplication with temperature? It will always increase by the same PROPORTION, won't it? So the physical logic still makes sense.
Rawr

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### Re: Kelvin vs. Celsius

But it's perfectly okay to multiply temperatures on an absolute scale. The problem is where the 0 of your temperature scale is somewhere else, bcause what multiplication really does is change the distance from zero.
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pnyxtr
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### Re: Kelvin vs. Celsius

But after having made control systems for cryocoolers for a couple of years, Celcius isn't more natural to me than Kelvin, it's obvious that it's just popular because it's a quite convenient scale for people. (The reasons for people to use Fahrenheit elude me, though, it's so incredibly impractical.)

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### Re: Kelvin vs. Celsius

How is Fahrenheit any less convenient for people than Celsius?
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cpt
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### Re: Kelvin vs. Celsius

gmalivuk wrote:How is Fahrenheit any less convenient for people than Celsius?

Because 0 is less arbitrary than 32.

kidding

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### Re: Kelvin vs. Celsius

0 is also less arbitrary than -17.77777...
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ajd007
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### Re: Kelvin vs. Celsius

Fahrenheit is nice because an average person's experience with temperature is going to be in the range of 0 to 100 degrees F. It's intuitive in the sense that 0 is probably the coldest temperature you've experienced, and 100 is probably the highest. It makes no sense for scientific uses, but it's very convenient for everyday usage.

PM 2Ring
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### Re: Kelvin vs. Celsius

ajd007 wrote:Fahrenheit is nice because an average person's experience with temperature is going to be in the range of 0 to 100 degrees F. It's intuitive in the sense that 0 is probably the coldest temperature you've experienced, and 100 is probably the highest. It makes no sense for scientific uses, but it's very convenient for everyday usage.

I think that'd depend on where you live. I've never experienced weather with temperatures below freezing. I don't think I'd want to live where the temperature got below 5°C on a regular basis; I think the coldest it got here last winter was 8°C. And while I'll agree that 100°F can be classed as rather hot, it's not unbearably hot. Add another 10°F onto that though, and I don't feel like doing very much. OTOH, I know guys that regularly work outdoors in such high temperatures.

FWIW, Australia changed from using Fahrenheit to Celsius when I was in my early teens. So I grew up being familiar with temperatures expressed in Fahrenheit, but these days I have to convert them to Celsius in order to make sense of them. In contrast, I can cope equally well with length measurements given in metric or imperial units.

But even though I'm much more comfortable these days dealing with temperatures expressed in Celsius, and agree that the definition of the Celsius scale is a bit more sensible than that of the Fahrenheit scale, I do think that the Fahrenheit degree is a more conveniently sized unit than the Celsius degree, at least when it comes to talking about the weather. Of course, our weather reports could state temperatures to the nearest half a degree, but they never do - it's always (rounded ?) to a whole number of degrees.

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### Re: Kelvin vs. Celsius

ajd007 wrote:Fahrenheit is nice because an average person's experience with temperature is going to be in the range of 0 to 100 degrees F.

I know preference of one scale over another is large cultural and subjective, but I have to disagree with this statement.

The lowest temperature you experience will depend hugely on where you live. In many places it'll never get anywhere close to 0 F. In others temperatures can drop far below them. Fahrenheit himself, who was from Poland / Germany / The Netherlands, must have experienced temperatures below 0 F. It's not common in those parts, but it does happen every few years.

The highest temperature the average person experiences on a regular basis however will definitely be above 100 F for everybody. Everybody cooks food, or has experience with boiling things in some way or form. And if you're running a fewer you're already above a 100 F.

The celsius scale is quite natural, I think, because the freezing and boiling of water are two very common and very important natural phenomena. Noone ever cares about the difference between -1F and +1F. But the difference between -1°C and +1°C, that is the difference between being well fed in the coming months, or dying of starvation because your entire crop just got destroyed. It is the difference between driving home safely, or dying in a carwreck because of glaze.
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yurell
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### Re: Kelvin vs. Celsius

To be fair, your last point is also true of Farenheit, just at a different point (31 - 33).
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### Re: Kelvin vs. Celsius

And in both cases it's not actually true on account of ice being able to exist above "freezing" and liquid water being able to exist below it. It's not as if entire crops die the second there's a bit of frost on them, nor do roads glaze over the second it drops below freezing.
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LaserGuy
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### Re: Kelvin vs. Celsius

Diadem wrote:The celsius scale is quite natural, I think, because the freezing and boiling of water are two very common and very important natural phenomena. Noone ever cares about the difference between -1F and +1F. But the difference between -1°C and +1°C, that is the difference between being well fed in the coming months, or dying of starvation because your entire crop just got destroyed. It is the difference between driving home safely, or dying in a carwreck because of glaze.

Doesn't everyone regularly need to use 1:1:1 mixtures of ice, water, and ammonium chloride in their daily lives?

jmorgan3
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### Re: Kelvin vs. Celsius

LaserGuy wrote:
Diadem wrote:The celsius scale is quite natural, I think, because the freezing and boiling of water are two very common and very important natural phenomena. Noone ever cares about the difference between -1F and +1F. But the difference between -1°C and +1°C, that is the difference between being well fed in the coming months, or dying of starvation because your entire crop just got destroyed. It is the difference between driving home safely, or dying in a carwreck because of glaze.

Doesn't everyone regularly need to use 1:1:1 mixtures of ice, water, and ammonium chloride in their daily lives?

I believe most northern Europeans drink this with breakfast.
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Tass
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### Re: Kelvin vs. Celsius

PM 2Ring wrote:I think that'd depend on where you live. I've never experienced weather with temperatures below freezing. I don't think I'd want to live where the temperature got below 5°C on a regular basis; I think the coldest it got here last winter was 8°C. And while I'll agree that 100°F can be classed as rather hot, it's not unbearably hot. Add another 10°F onto that though, and I don't feel like doing very much. OTOH, I know guys that regularly work outdoors in such high temperatures.

37°C is not unbearably hot?? I prefer it to stop at 25°C, the few summer days where it climbs to 30 are not nice.

jmorgan3 wrote:
LaserGuy wrote:Doesn't everyone regularly need to use 1:1:1 mixtures of ice, water, and ammonium chloride in their daily lives?

I believe most northern Europeans drink this with breakfast.

We do like ammonium chloride, but not that much.

yurell
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### Re: Kelvin vs. Celsius

Tass wrote:37°C is not unbearably hot?? I prefer it to stop at 25°C, the few summer days where it climbs to 30 are not nice.

Don't spend summer here, where almost every day is 30+ and a good chunk of that is 35+, with the occasional burst of 40+ (which I'm sure we can all agree is uncomfortable).
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### Re: Kelvin vs. Celsius

People deal with ice on roads and snow more often than they deal with frozen brine.
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Darryl
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### Re: Kelvin vs. Celsius

ajd007 wrote:Fahrenheit is nice because an average person's experience with temperature is going to be in the range of 0 to 100 degrees F. It's intuitive in the sense that 0 is probably the coldest temperature you've experienced, and 100 is probably the highest. It makes no sense for scientific uses, but it's very convenient for everyday usage.

As others have said, that's entirely dependent on location. My range of experience is from about -10 F to 90 F. -30 F on the low end if we're counting wind-chill.
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PM 2Ring
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### Re: Kelvin vs. Celsius

Tass wrote:
PM 2Ring wrote:I think that'd depend on where you live. I've never experienced weather with temperatures below freezing. I don't think I'd want to live where the temperature got below 5°C on a regular basis; I think the coldest it got here last winter was 8°C. And while I'll agree that 100°F can be classed as rather hot, it's not unbearably hot. Add another 10°F onto that though, and I don't feel like doing very much. OTOH, I know guys that regularly work outdoors in such high temperatures.

37°C is not unbearably hot?? I prefer it to stop at 25°C, the few summer days where it climbs to 30 are not nice.

Pfft! 30°C is nothing. It's not unusual during a hot spell here for the temperature to stay above 30°C for several days in a row, although I will admit it's not so easy to get to sleep in weather like that without air conditioning. I'm currently living in the sub-tropical part of Australia, but they get temperatures like that even in the southern parts of the country, and it can get really unpleasant away from the coast, where they don't get the benefit of the coastal humidity or sea breezes. Australia may be hotter than Denmark, but my Scandinavian ancestors managed ok, and that was in the days before aircon.

The warm climate might seem too hot for you, but the wildlife seem to like it. I get lots of birds visiting my bird-bath, including (at least) 4 species of parrot. [ Hi, Rasmine! ]

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### Re: Kelvin vs. Celsius

PM 2Ring wrote:The warm climate might seem too hot for you, but the wildlife seem to like it.
Well yeah, but the same can be said for undersea thermal vents.
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PM 2Ring
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### Re: Kelvin vs. Celsius

gmalivuk wrote:
PM 2Ring wrote:The warm climate might seem too hot for you, but the wildlife seem to like it.
Well yeah, but the same can be said for undersea thermal vents.

I'll let you get away with that remark since you have personal experience of this wide brown land. Or am I mis-remembering, and you only visited NZ?

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### Re: Kelvin vs. Celsius

PM 2Ring wrote:* gathers up several huntsman spiders to email to gmal *

Gmail dis-activated my account for doing exactly that. You might want to create a throwaway account for emailing any living beings.
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LaserGuy
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### Re: Kelvin vs. Celsius

ajd007 wrote:Fahrenheit is nice because an average person's experience with temperature is going to be in the range of 0 to 100 degrees F. It's intuitive in the sense that 0 is probably the coldest temperature you've experienced, and 100 is probably the highest. It makes no sense for scientific uses, but it's very convenient for everyday usage.

To add to the anecdote lists, in the winter here in Ottawa, we hit -30C (-22F) a few times a year. If you count windchill, we average about 2-3 weeks below -30C. If you're in the Canadian prairie provinces, or certainly anywhere up North, you'll occasionally be treated to days in the -40C range.

drj
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### Re: Kelvin vs. Celsius

It's like distances, in the following analogy: Is 2nd street in Manhattan twice as far from San Francisco as 1st street? Obviously not. Same way 2 degrees Celsius is not twice as hot as 1 degree C. Two degrees IS twice as far from 0 degrees C as 1 degree is, but that's all.

Me, I prefer degrees Reaumur - used in the famous infograph of Napoleons retreat from Russia. http://en.wikipedia.org/wiki/File:Minard.png

pnyxtr
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### Re: Kelvin vs. Celsius

PM 2Ring wrote:Pfft! 30°C is nothing. :) It's not unusual during a hot spell here for the temperature to stay above 30°C for several days in a row, although I will admit it's not so easy to get to sleep in weather like that without air conditioning. I'm currently living in the sub-tropical part of Australia, but they get temperatures like that even in the southern parts of the country, and it can get really unpleasant away from the coast, where they don't get the benefit of the coastal humidity or sea breezes. Australia may be hotter than Denmark, but my Scandinavian ancestors managed ok, and that was in the days before aircon. :)

The warm climate might seem too hot for you, but the wildlife seem to like it. I get lots of birds visiting my bird-bath, including (at least) 4 species of parrot. [ Hi, Rasmine! ]

Given that it does get up to 35 or above here, your Scandinavian ancestors would have had to live somewhere other than Scandinavia to not experince those temperatures. Also, we can get -35, no sweat. Maybe not where I live (thankfully), but there are many places where it goes way below that.

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### Re: Kelvin vs. Celsius

gmalivuk wrote:And in both cases it's not actually true on account of ice being able to exist above "freezing" and liquid water being able to exist below it. It's not as if entire crops die the second there's a bit of frost on them, nor do roads glaze over the second it drops below freezing.

You're being unnecessarily pedantic here. All these effects may not happen at exactly 0, but they certainly happen around zero. You can't deny that zero degrees Celsius is a really important temperature, while zero degrees Fahrenheit has no significance whatsoever. So my point stands.
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### Re: Kelvin vs. Celsius

Diadem wrote:You're being unnecessarily pedantic here. All these effects may not happen at exactly 0, but they certainly happen around zero. You can't deny that zero degrees Celsius is a really important temperature, while zero degrees Fahrenheit has no significance whatsoever. So my point stands.

You can't deny that 32 degrees Fahrenheit is a really important temperature, while 32 degrees Celsius has no significance whatsoever. So what's your point?
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### Re: Kelvin vs. Celsius

Right, do I really have to explain the difference between 0 and 32?
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### Re: Kelvin vs. Celsius

You have to explain why that distinction is important in this context.
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### Re: Kelvin vs. Celsius

But after having made control systems for cryocoolers for a couple of years, Celcius isn't more natural to me than Kelvin, it's obvious that it's just popular because it's a quite convenient scale for people. (The reasons for people to use Fahrenheit elude me, though, it's so incredibly impractical.)

You're missing an important factor of Fahrenheit. It is more granular than Celcius. Every degree Celsius is equal to 1.8 degrees Fahrenheit.

Also, 100 = fever is a very handy quick rule of thumb.
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### Re: Kelvin vs. Celsius

yurell wrote:You have to explain why that distinction is important in this context.
I'm putting 3:1 odds that you are trolling. But it could be that you are just confused.

0 is an important point on the number line. It coinciding with an important part on the scale you are measuring is a good thing. It not coinciding with an important point is a bad thing. 32 is not an important point on the number line. 0F being an uninteresting point is a misfeature of that scale. 0C being an interesting point is a good feature of that scale. 0K being an even more interesting point is an even better feature of that scale.
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### Re: Kelvin vs. Celsius

Yakk wrote:0 is an important point on the number line. It coinciding with an important part on the scale you are measuring is a good thing. It not coinciding with an important point is a bad thing.

Why is it a bad thing? Why does every scale have a significant point at 0? The zero-point for Fahrenheit was chosen around the freezing point of a brine solution, which Fahrenheit thought was a good idea because it stabilises very rapidly which in turn allowed for an accurate gauge in temperature at the time. Furthermore, he was attempting to fit a scale to agree with the one invented by another scientist. Why should the freezing point of water at one atmosphere of pressure be any less arbitrary? In fact, it's not even that any more — 0 degrees Celsius isn't defined in relation to water (although it was), it is defined as being 271.15K. To me, 271.15 sounds just as unimportant as 32, but maybe that's just me.
In fact, why don't you set Standard Temperature and Pressure to be the zero-point in your temperature scale? It's just as arbitrary as the freezing point ofwater water.

Even more strongly, I can understand it being preferable to have the zero-point on a scale being some important land mark (which it is in Fahrenheit too, I will point out, for the purposes Fahrenheit was employing), but why is it bad for it to not coincide with an important point? 0K coincides with what is probably the most important temperature in the Universe, so does this make Celsius 'bad', because it's not corresponding to a suitably important point?

Personally, I prefer Celsius, since it's what I've grown up with, what I know and the division between 0 freezes while 100 boils is an intuitive and reasonable one, and I dislike Fahrenheit. What I dislike more, though, is simply asserting that because 0 is the freezing point of water, it is objectively better to use a scale that sits its zero point there than the freezing point of another substance. Even worse, also assert that it is bad to have '0' set with a 'not important point' without any arguments to support that, either.

Yakk wrote:32 is not an important point on the number line. 0F being an uninteresting point is a misfeature of that scale.

Uninteresting to you, maybe. The fact that Fahrenheit and his contemporaries chose it may indicate that it's not as uninteresting as you think, even if it was for purely academic / historical reasons.

Yakk wrote:0C being an interesting point is a good feature of that scale. 0K being an even more interesting point is an even better feature of that scale.

I agree on both these points. However, not having that particular 'good' feature doesn't make it 'bad' by default.
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### Re: Kelvin vs. Celsius

yurell wrote:
Yakk wrote:0 is an important point on the number line. It coinciding with an important part on the scale you are measuring is a good thing. It not coinciding with an important point is a bad thing.
Why is it a bad thing?
Because it throws away a useful signal to the user of the scale. It is wasteful.
Why does every scale have a significant point at 0? The zero-point for Fahrenheit was chosen around the freezing point of a brine solution, which Fahrenheit thought was a good idea because it stabilises very rapidly which in turn allowed for an accurate gauge in temperature at the time. Furthermore, he was attempting to fit a scale to agree with the one invented by another scientist.
Which is utterly unimportant to the user of the scale. Unless their goal is to make thermometers, or there is a high-salt brine port nearby whose freezing is of high concern. Ie, corner cases.
Why should the freezing point of water at one atmosphere of pressure be any less arbitrary? In fact, it's not even that any more — 0 degrees Celsius isn't defined in relation to water (although it was), it is defined as being 271.15K. To me, 271.15 sounds just as unimportant as 32, but maybe that's just me.
Also utterly unimportant to the user of the scale.
In fact, why don't you set Standard Temperature and Pressure to be the zero-point in your temperature scale? It's just as arbitrary as the freezing point ofwater water.
We are water based organisms living on a planet where the biosphere varies around 3 of the phases of water (vapor, less so). These points are sharp discontinuities in how we interact with temperature at these points.
Even more strongly, I can understand it being preferable to have the zero-point on a scale being some important land mark
Yes, preferable. So it is a good thing if it happens, and a bad thing if it doesn't.
but why is it bad for it to not coincide with an important point?
The waste of a good thing is a bad thing.
0K coincides with what is probably the most important temperature in the Universe, so does this make Celsius 'bad', because it's not corresponding to a suitably important point?
I stated that 0K being an important temperature is a good thing. You even quoted me as saying it right below.

As the intended users of the Kelvin and Celsius scale are different, how good the various choices are vary. As absolute zero, and ideal gas equation calculations, and the like are rarely something I use in my daily life, there are many ways in which absolute zero is not important to my non-scientific use of temperature.
Uninteresting to you, maybe. The fact that Fahrenheit and his contemporaries chose it may indicate that it's not as uninteresting as you think, even if it was for purely academic / historical reasons.
No, uninteresting to everyday use of Fahrenheit for temperature reasons.
I agree on both these points. However, not having that particular 'good' feature doesn't make it 'bad' by default.

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Last edited by JHVH on Fri Oct 23, 4004 BCE 6:17 pm, edited 6 times in total.

LaserGuy
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### Re: Kelvin vs. Celsius

Darryl wrote:

But after having made control systems for cryocoolers for a couple of years, Celcius isn't more natural to me than Kelvin, it's obvious that it's just popular because it's a quite convenient scale for people. (The reasons for people to use Fahrenheit elude me, though, it's so incredibly impractical.)

You're missing an important factor of Fahrenheit. It is more granular than Celcius. Every degree Celsius is equal to 1.8 degrees Fahrenheit.

Also, 100 = fever is a very handy quick rule of thumb.

You can just use decimals in Celsius if you need more precision...

gmalivuk
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### Re: Kelvin vs. Celsius

yurell wrote:0 degrees Celsius isn't defined in relation to water (although it was), it is defined as being 271.15K.
Then again, Kelvin is defined so the triple point of water is exactly 273.16K, and then Celsius is such that the triple point is at 0.01 and absolute zero is -273.15.
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