4 ms·

I’ll never stop being fascinated by how neatly all of this fits together: take a hollow cube that has 10cm long edges. Fill it with water - now you have a liter

I’ll never stop being fascinated by how neatly all of this fits together: take a hollow cube that has 10cm long edges. Fill it with water - now you have a liter of water. It weighs 1kg. Put it into the freezer, when it just starts freezing, it’s 0°C. Put it onto a stove, and when it starts boiling, it’s 100°C. Simple as that.

defrost 3y ago
> Put it onto a stove, and when it starts boiling, it’s 100°C. Simple as that. Not quite - don't forget your elevation | air pressure. Of course not even elevation above mean sea level is straightforward .. what is the MSL of Australia, for example, and how does it relate to the Geoid, the long tidal run through the long narrow straits to the north of Australia, the WGS ellipsoid, etc.
- jeffchien 3y ago
  Not to mention the dissolved solids as well, so it's not as simple as using tap water. IMHO Celsius is the SI unit least deserving of praise. It's just bolted onto the system through the Boltzmann constant and isn't intricately linked like other SI/CGS units. It's also a little too coarse for modern use. Sure, I could use decicelsius myself, but that doesn't stop every other weather station, AC/thermostat manufacturer, etc. from still using whole degrees. You can buy $2000 Italian espresso machines with elaborate PID controllers that can only be tuned to whole degrees, which ironically means that using Fahrenheit is more precise!
  - triactual 3y ago
    The isotopic content of the water matters too. Boiling point are not used to calibrate thermometers though. Freeze points and triple points are used for temperature calibration. And outside of a primary standards lab, it’s usually just a transfer standard (another, more accurate thermometer).
  - pocketarc 3y ago
    I think there’s some confusion here - the Kelvin is the SI unit of temperature, not Celsius.
  - arlort 3y ago
    Besides Celsius not being the SI unit. I'd be shocked if weather forecasting is ever precise to less than 1-2 °C
    - defrost 3y ago
      > I'd be shocked if weather forecasting is ever precise to less than 1-2 °C That's not a forecast .. actual forecasts for a region are often more accurate than that wrt "mean tempreture" for that region. Where I live the BoM (Bureau of Meteorology) cannot "accurately" predict the upcoming daily tempreture and rainfall for the town that I'm in. They do very accurately predict the mean temp. and rainfall for the wider region. Doppler RADAR gives a very accurate measure of the amount of moisture held by rain bearing clouds, stable wrt broad area winds give a good path for that moisture's travel in the next 12-24 hours, experience + data give solid predictions for the amount of water to be shed, along with bulk cooling from shade and water fall + evaporation. The difficulty rarely lies in the bulk parameters for a broad area, the devil is in the small details which are inherently turbulent. To measure the accuracy of forecasting it first has to be ring fenced by what area you intend to predict the mean attributes for, the timescale you intend to project for, etc.
      - arlort 3y ago
        Yes, but all of that is unrelated to the original point The commenter I replied to was complaining about weather stations not using decimals. As you point out we can predict averages with a better accuracy, but services which have that accuracy do use decimals, where decimals aren't used is in consumer weather forecasts where an accuracy of less than 1 degree is anyway useless because > the devil is in the small details which are inherently turbulent
    - Ekaros 3y ago
      Also temperature is variable. It fluctuates through the day and then things like clouds or rains can drop it quite a lot or keep it higher during winters in parts of the world. You can get pretty good hour level forecast in some scenarios. But how do you effectively communicate those outside showing some type of graph...
  - The_Colonel 3y ago
    The only use case I encountered where Celsius is too coarse is measuring body temperature.
  - eqvinox 3y ago
    > doesn't stop every other weather station, AC/thermostat manufacturer, etc. from still using whole degrees I am European and while I agree on weather stations, I have never seen an AC or thermostat that doesn't at least use 0.5°C increments. (And I'd argue a whole °C is perfectly appropriate for weather.)
javawizard 3y ago
It gets even better: take that 1kg of water at 0°C, add 100 kilocalories of heat energy, and it's now 100°C and just about to boil. (That's assuming you're at sea level, as another commenter noted - if you're at 5,000 feet, the boiling point of water is something like 95°C.)
akira2501 3y ago
If you do this at Sea Level when Air Pressure is the barometric mean pressure with nothing but H2O, yes. Otherwise, not exactly, in ways that require formulas to quantify. Metrology is the dirtiest of all sciences, it does not grant simplicity. Anyways.. the counter example was the old definition of the Ampere: "the constant current which, if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed one metre apart in a vacuum, would produce between these conductors a force equal to 2 × 10−7 newton per metre of length." Perfectly unrealizable within this Universe.
tzs 3y ago
It has some warts. A mole of electrons has a charge of about 96487 coulombs. 100000 would have been nicer.

defrost 3y ago

> Put it onto a stove, and when it starts boiling, it’s 100°C. Simple as that. Not quite - don't forget your elevation | air pressure. Of course not even elevation above mean sea level is straightforward .. what is the MSL of Australia, for example, and how does it relate to the Geoid, the long tidal run through the long narrow straits to the north of Australia, the WGS ellipsoid, etc.

jeffchien 3y ago
Not to mention the dissolved solids as well, so it's not as simple as using tap water. IMHO Celsius is the SI unit least deserving of praise. It's just bolted onto the system through the Boltzmann constant and isn't intricately linked like other SI/CGS units. It's also a little too coarse for modern use. Sure, I could use decicelsius myself, but that doesn't stop every other weather station, AC/thermostat manufacturer, etc. from still using whole degrees. You can buy $2000 Italian espresso machines with elaborate PID controllers that can only be tuned to whole degrees, which ironically means that using Fahrenheit is more precise!
- triactual 3y ago
  The isotopic content of the water matters too. Boiling point are not used to calibrate thermometers though. Freeze points and triple points are used for temperature calibration. And outside of a primary standards lab, it’s usually just a transfer standard (another, more accurate thermometer).
- pocketarc 3y ago
  I think there’s some confusion here - the Kelvin is the SI unit of temperature, not Celsius.
- arlort 3y ago
  Besides Celsius not being the SI unit. I'd be shocked if weather forecasting is ever precise to less than 1-2 °C
  - defrost 3y ago
    > I'd be shocked if weather forecasting is ever precise to less than 1-2 °C That's not a forecast .. actual forecasts for a region are often more accurate than that wrt "mean tempreture" for that region. Where I live the BoM (Bureau of Meteorology) cannot "accurately" predict the upcoming daily tempreture and rainfall for the town that I'm in. They do very accurately predict the mean temp. and rainfall for the wider region. Doppler RADAR gives a very accurate measure of the amount of moisture held by rain bearing clouds, stable wrt broad area winds give a good path for that moisture's travel in the next 12-24 hours, experience + data give solid predictions for the amount of water to be shed, along with bulk cooling from shade and water fall + evaporation. The difficulty rarely lies in the bulk parameters for a broad area, the devil is in the small details which are inherently turbulent. To measure the accuracy of forecasting it first has to be ring fenced by what area you intend to predict the mean attributes for, the timescale you intend to project for, etc.
    - arlort 3y ago
      Yes, but all of that is unrelated to the original point The commenter I replied to was complaining about weather stations not using decimals. As you point out we can predict averages with a better accuracy, but services which have that accuracy do use decimals, where decimals aren't used is in consumer weather forecasts where an accuracy of less than 1 degree is anyway useless because > the devil is in the small details which are inherently turbulent
  - Ekaros 3y ago
    Also temperature is variable. It fluctuates through the day and then things like clouds or rains can drop it quite a lot or keep it higher during winters in parts of the world. You can get pretty good hour level forecast in some scenarios. But how do you effectively communicate those outside showing some type of graph...
- The_Colonel 3y ago
  The only use case I encountered where Celsius is too coarse is measuring body temperature.
- eqvinox 3y ago
  > doesn't stop every other weather station, AC/thermostat manufacturer, etc. from still using whole degrees I am European and while I agree on weather stations, I have never seen an AC or thermostat that doesn't at least use 0.5°C increments. (And I'd argue a whole °C is perfectly appropriate for weather.)

javawizard 3y ago

It gets even better: take that 1kg of water at 0°C, add 100 kilocalories of heat energy, and it's now 100°C and just about to boil. (That's assuming you're at sea level, as another commenter noted - if you're at 5,000 feet, the boiling point of water is something like 95°C.)

akira2501 3y ago

If you do this at Sea Level when Air Pressure is the barometric mean pressure with nothing but H2O, yes. Otherwise, not exactly, in ways that require formulas to quantify. Metrology is the dirtiest of all sciences, it does not grant simplicity. Anyways.. the counter example was the old definition of the Ampere: "the constant current which, if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed one metre apart in a vacuum, would produce between these conductors a force equal to 2 × 10−7 newton per metre of length." Perfectly unrealizable within this Universe.

tzs 3y ago

It has some warts. A mole of electrons has a charge of about 96487 coulombs. 100000 would have been nicer.