Your pet peeve, technical or otherwise.

[Analog Kid]

Not necessarily invalid, but only about as accurate as, say, a weight-guesser at a carnival.
(Although who knows? they might actually be pretty good at it.)

[TimFox]

IMO it is not foreign the idea of saying that "today the temperature dropped to half of what it was yesterday" - i.e., 50% less.
Sure, in a typical conversation no one would come up with additional fraction numbers such as 25 or 33%, but that does not invalidate the use of percentages for temperatures.

That statement is meaningless.  Also, I have never heard anything in typical conversation except that it will be, say, 10 degrees cooler tomorrow.
When would someone use a percentage in this context?

[Analog Kid]

IMO it is not foreign the idea of saying that "today the temperature dropped to half of what it was yesterday" - i.e., 50% less.
Sure, in a typical conversation no one would come up with additional fraction numbers such as 25 or 33%, but that does not invalidate the use of percentages for temperatures.

That statement is meaningless.  Also, I have never heard anything in typical conversation except that it will be, say, 10 degrees cooler tomorrow.
When would someone use a percentage in this context?

Yep. At the very least "today the temperature dropped to half of what it was yesterday" is an ... odd sort of statement, one that I've never heard anybody utter in my lifetime. I suppose you could use it colloquially, like "it's raining cats and dogs", but with about the same amount of realism.

[rsjsouza]

Descend from your pedantic high horses and stop thinking about kinetic energy of molecules and instead look on how regular people think about ratios, numbers and quantities. This is a regular expression where I come from (Brasil) and I have used and heard this many times, even here in the USofA. Blame on a specific climate where temperatures can go from "X" to "2 × X" in a single day (or vice-versa).

[Analog Kid]

Descend from your pedantic high horses and stop thinking about kinetic energy of molecules and instead look on how regular people think about ratios, numbers and quantities. This is a regular expression where I come from (Brasil) and I have used and heard this many times, even here in the USofA. Blame on a specific climate where temperatures can go from "X" to "2 × X" in a single day (or vice-versa).

OK. Never, ever heard that myself (and I've lived in places where there are huge temperature swings). But I'll accept it as a colloquialism. Like "it's so dry out there the trees follow the dogs around".

[CatalinaWOW]

I'll accept it as a local expression, though I have never heard it, even living at various times in the crazy climate extremes of various parts of the western US.  I have seen outdoor temperatures of -40 (C or F) and +53 C (128 F) and seen huge daily swings and bigger changes when a weather front sweeps through and the people around me hadn't adopted that way of describing it.  Colder than a witches tit, or hot enough to fry eggs and many other colorful expressions, but not that semi-quantitative description.

But the fact that people use these expressions don't mean they are useful for engineering, and should only be used for emotional context.  I have heard people from various locations compare the local mosquitos to light planes, or even military bombers.  But no one thinks of picking a fly swatter based on those comparisons, or designing a mosquito net to resist such.

[coppercone2]

Descend from your pedantic high horses and stop thinking about kinetic energy of molecules and instead look on how regular people think about ratios, numbers and quantities. This is a regular expression where I come from (Brasil) and I have used and heard this many times, even here in the USofA. Blame on a specific climate where temperatures can go from "X" to "2 × X" in a single day (or vice-versa).

OK. Never, ever heard that myself (and I've lived in places where there are huge temperature swings). But I'll accept it as a colloquialism. Like "it's so dry out there the trees follow the dogs around".

he basically told you to shut up and act stupid, on a physics forum, a pet peeve of mine when someone does that, good advise to follow if your a minion at gas station

[PlainName]

But the fact that people use these expressions don't mean they are useful for engineering

Who has suggested they're useful for engineering?

[Siwastaja]

This is a regular expression where I come from (Brasil) and I have used and heard this many times, even here in the USofA. Blame on a specific climate where temperatures can go from "X" to "2 × X" in a single day (or vice-versa).

Yeah. I would guess that "normal" people would use it whenever the temperature values involved happen to be in the correct range for the comparison to "feel" meaningful.

Like, temperature "halving" from +36degC to +18degC would be somewhat understandable. Or from -40degC to -20degC. The differences in how you need to clothe, how much heating or cooling your house is going to need, psychological (arbitrary) ratio is something 50%-ish.

This of course does not generalize, which is exactly the reason you won't hear that often. Many people intuitively understand it does not generalize and never say so. Those who would use this expression would intuitively do it only with certain values. Definitely not when comparing e.g. +6degC to +3degC.

[PlainName]

Yeah. I would guess that "normal" people would use it whenever the temperature values involved happen to be in the correct range for the comparison to "feel" meaningful.

I wonder if that's why there are so many saying they've never heard it: they are nearly all Americans (or US relative) so use F, and that sort of comparison just doesn't occur in F. The ones that are amenable to it would, I suggest, use C.

[helius]

The situations are more or less the same. In °F, it could be 60 degrees during the day and 30 at night (especially in November).
I submit that whether someone uses this misbegotten expression ("half as hot") has more to do with physics literacy than anything else.

[TimFox]

The situations are more or less the same. In °F, it could be 60 degrees during the day and 30 at night (especially in November).
I submit that whether someone uses this misbegotten expression ("half as hot") has more to do with physics literacy than anything else.

That's typical weather for Chicago in November:  everyone here would say 30 degrees colder.

[Analog Kid]

^Yes; I think we can confidently say that while some people have at some point heard someone utter the phrase "it's twice as (hot/cold) as X", that this is an outlier and uncommon.

Question to those who have heard this said: how often have you heard this said? I'm guessing not very.

[Siwastaja]

^Yes; I think we can confidently say that while some people have at some point heard someone utter the phrase "it's twice as (hot/cold) as X", that this is an outlier and uncommon.

Question to those who have heard this said: how often have you heard this said? I'm guessing not very.

I agree it would be outliers. Now that I think hard enough I can imagine maybe having heard it once or twice in my life. Much more often it's a meta discussion like this one about "why you can't say so", instead of someone actually saying so.

In Finnish we have a separate word for "negative (in Celsius) temperature", "pakkanen"; with it the spoken numbers act like absolute values because the sign comes from the word itself. Like, -30degC is "30 degrees pakkanen". So the polarity of comparisons swap in an interesting way. In this context, when it warms up from -30 to -15, someone might have said that pakkanen halved. And with these kind of numbers maybe it means you can reduce amount of clothing if not by 50%, still something roughly that order of magnitude. Or the time-to-hypothermia would double. But when going from -4 to -2 degC, no one would ever say that "pakkanen" is halving.

[Circlotron]

In Finnish we have a separate word for "negative (in Celsius) temperature", "pakkanen"; with it the spoken numbers act like absolute values because the sign comes from the word itself. Like, -30degC is "30 degrees pakkanen".

Similarly in English we sat “30 below zero” or more commonly, just “30 below”.

[TimFox]

Another term in English, now uncommon, is "of frost" (below freezing):  i.e., 10^o Fahrenheit of frost is +22^o.

[Nominal Animal]

In Finnish we have a separate word for "negative (in Celsius) temperature", "pakkanen"; with it the spoken numbers act like absolute values because the sign comes from the word itself. Like, -30degC is "30 degrees pakkanen".

It is informative to note that "pakkanen" is a native word, likely thousands of years old (some other words are loans from proto-Germanic and proto-Slavic, like "kuningas" for king), and refers to both the state where pure water freezes, and to how much it affects things.

When the temperature is very, very cold, it is described as "kova pakkanen" or "kireä pakkanen" or "pureva pakkanen" (hard, tight, biting, respectively).  This correlates to how ice (and metals) get much stronger the colder there is.  (I've often wondered why cryoannealing tool steel in liquid nitrogen isn't more common: it's cheap, and quite effective in increasing strength and reducing brittleness in most alloys.  Ice itself can be called steel ice, "teräsjää", when it is very pure and very cold, and therefore very strong.)

The situation when it is already "pakkanen" but it is getting colder, is said to be tightening: "pakkanen kiristyy".
When a spell of "pakkanen" ends, and it starts becoming less cold (but still below freezing), it is said to fold: "pakkanen taittuu", and then "ilma lauhtuu" (air gets gentler).

In this sense, when someone says "pakkanen puolittui" (halved), it rarely refers to the exact Celsius scale temperature values, but more to how it feels like, and what kind of actions one needs to do to survive (or have their pets/lifestock/friends survive), and so on.  For example, my mom often says something along the lines of 'the thermometer says X degrees, but it actually is "kovempi pakkanen" than that', to refer to the combined effects of temperature and cloudlessness (cloudless sky during winter nights having a temperature below -55°C there).  Effect of wind is usually noted separately.  She's kept a diary of notable weather changes for the last four decades or so, too.

I don't think this is a Finnish peculiarity, either, and would be recognizable/intuitive to any pre-thermometer scale culture in a similar climate.  It just happens to fit well into the Celsius scale.  However, Anders Celsius was Swedish, and I bet in 1742 Swedish had very similar idioms in wide use; Uppsala, Sweden, having the same climate as southernmost parts of Finland nearby.  I do not think that the choice of liquid water was at all arbitrary, and was simply thoroughly intuitive choice for him.

[TimFox]

Of course, Anders Celsius’ original thermometer had 0 at boiling and 100 at freezing, so I’m not sure what “half” would mean.

[Analog Kid]

Of course, Anders Celsius’ original thermometer had 0 at boiling and 100 at freezing, so I’m not sure what “half” would mean.

I find that hard to believe. Oh, I'm not disputing you at all; it just seems so counterintuitive. Was Celsius that out of touch with ordinary human reality? or even with basic thermodynamics, which even during his lifetime recognized that increased temperature meant increased energy.

[TimFox]

Of course, Anders Celsius’ original thermometer had 0 at boiling and 100 at freezing, so I’m not sure what “half” would mean.

I find that hard to believe. Oh, I'm not disputing you at all; it just seems so counterintuitive. Was Celsius that out of touch with ordinary human reality? or even with basic thermodynamics, which even during his lifetime recognized that increased temperature meant increased energy.

It’s true.  Some objected to renaming “Centigrade” to “Celsius”, but it conserved the initial letter.  Celsius died in 1744.  Classical thermodynamics (long before statistical mechanics) starts with Carnot in 1824.

[BlownUpCapacitor]

When major political events occur, the internet gets absolutely flooded about it. At least it got the images and video correct...

The results are better if I actually include the brand name though.

[shapirus]

I wonder if that's why there are so many saying they've never heard it: they are nearly all Americans (or US relative) so use F, and that sort of comparison just doesn't occur in F. The ones that are amenable to it would, I suggest, use C.

The Fahrenheit scale is as widely used as the Chinese script where I live (actually, not even as much as that, considering all the Chinese gadgets coming with untranslated manuals from Aliexpress lol), and even though everyone thinks in °C here, I have never ever heard anyone use ratios, like "half the temperature" or "twice the temperature" to describe the amount of change, at least outside of scientific areas where, of course, the absolute temperature scale would be referred to.

So I am quite surprised hearing that there are places where it's actually used.

[vk6zgo]

I wonder if that's why there are so many saying they've never heard it: they are nearly all Americans (or US relative) so use F, and that sort of comparison just doesn't occur in F. The ones that are amenable to it would, I suggest, use C.

The Fahrenheit scale is as widely used as the Chinese script where I live (actually, not even as much as that, considering all the Chinese gadgets coming with untranslated manuals from Aliexpress lol), and even though everyone thinks in °C here, I have never ever heard anyone use ratios, like "half the temperature" or "twice the temperature" to describe the amount of change, at least outside of scientific areas where, of course, the absolute temperature scale would be referred to.

So I am quite surprised hearing that there are places where it's actually used.

When I was a kid airconditioning in movie theatres in Oz was relatively rare, with many suburban theatres having an "open air" alternative for the hot summer nights.

In the city, there were a number of normal movie theatres which were open day & night, some of which had airconditioning, but most didn't.
Those that did made a big deal about it with signs saying "airconditioned".
The idea seemed to be not only to be airconditioned, but to really "rub it in".

To that end, they wound the aircond down so cold that after a while the customers started to shiver, so you got the strange situation where customers carried jackets & cardigans even though it was 38c outside.

Around this time, I noticed in US publications like "Life" that when movie theatres appeared in Summer street scenes, they often had signs saying things like "20% cooler inside", which intrigued me, as our movie houses didn't try to give a figure.

[TimFox]

This history of movie theater air-conditioning in the US  https://www.ashrae.org/file%20library/technical%20resources/ashrae%20journal/125thanniversaryarticles/044-053_chang_historical.pdf  points out that the marketing slogan was "20 degrees cooler inside"  (see p 49 of the article).

[Analog Kid]

This history of movie theater air-conditioning in the US  https://www.ashrae.org/file%20library/technical%20resources/ashrae%20journal/125thanniversaryarticles/044-053_chang_historical.pdf  points out that the marketing slogan was "20 degrees cooler inside"  (see p 49 of the article).

I'm sure that doesn't preclude the possibility of some marketing genius somewhere claiming "20% cooler". Those idiots always seem to misuse the concept of proportion. "30% more power": more power than what?