Fahrenheit vs Celsius

1. Oct 15, 2012

SW VandeCarr

A meteorologist friend of mind told me a story about an American who owned a condominium overseas. The owner got an email from the caretaker saying the temperature in his condo was 32 degrees and for asked permission to turn on the air conditioning and set the thermostat to 28. The owner promptly replied:"ARE YOU CRAZY!? Turn on the heater and set the thermostat to 55 right now!" Angry at receiving such a rude reply, the caretaker dutifully complied, even to the extent of replacing the heater thermostat with one for an electric oven that could be set at 55 C (131 F).

It's not clear if the story is true or just part of meteorological lore, but my friend does think that the real choice is between Fahrenheit or Kelvin. He points out if a relative scale must be used, Fahrenheit is better because it's a finer scale (1C=1.8F). The fact that Celsius is scaled to the phase transitions of water is merely an aesthetic advantage in his view. Besides, there are no recognized named multiples or divisions of the Celsius/Kelvin degree. It's not really a metric unit.

So are Americans really right to hold out and not adopt the Celsius scale for weather reports, cooking and taking your body temperature?

Last edited: Oct 15, 2012
2. Oct 15, 2012

AlephZero

Fahrenheit vs Kelvin?? Don't you mean Rankine and Kelvin? (They both have 0 at absolute zero). Or Fahrenheit and Celsius?

FWIW I've had fun and games with US propulsion engineers supplying us with temperatures in R, but not bothering to state the unit. And ignoring the "K" on data we sent to them, because they thought it was a typo.

3. Oct 15, 2012

Staff: Mentor

The actual measurement of temperature is the same no matter what you use, so in terms of accuracy and precision it doesn't matter which unit you use.

4. Oct 15, 2012

SW VandeCarr

My friend means Kelvin for scientific work and as I said, if you must use a relative scale for everyday uses, Fahrenheit has a finer scale. You get a more precise reading for the same number of characters. He doesn't want to replace Kelvin with Rankin. Kelvin is well established everywhere, but Celsius is not widely used by the general public in the US and my friend thinks nothing practical would be gained by switching to it.

EDIT: I think my friend wants to use Kelvin exclusively in meteorology, including weather reports, but if that can't be done, he believes it's better to stick with Fahrenheit.

Last edited: Oct 15, 2012
5. Oct 15, 2012

Astronuc

Staff Emeritus
The Fahrenheit scale is also an arbitrary scale with the phase changes of water, the melting/freezing point and boiling point separated by 180°F/°R. It's just as arbitrary as 100°C/K.

I have to use both English/British and SI/MKS (and occasionally cgs) systems in my work, but I prefer metric.

6. Oct 15, 2012

Staff: Mentor

That's just silly. Hasn't he heard of decimals?
Even if the first thing were true, which it isn't, it wouldn't be relevant to the second, which is also wrong.

http://en.wiktionary.org/wiki/millikelvin

7. Oct 15, 2012

Staff: Mentor

Right: depends on the instrument.

8. Oct 15, 2012

SW VandeCarr

OK. He's a research based meteorologist. I think his point is that in published weather reports the number of characters is fixed. If you say 1 C, it could be 1 F or 2 F because you don't have the option of using decimal fractions. This is quite common.

Last edited: Oct 15, 2012
9. Oct 15, 2012

Staff: Mentor

Are weather models precise enough for that to matter? Or does the extra precision in the presentation provide a false sense of precision in the prediction?

Also, climate data is published by the government in a precision of .1C: http://www.nrel.gov/docs/fy08osti/43156.pdf

So perhaps it is just the day-to-day weather forecasts that are lower precision.

10. Oct 15, 2012

Staff: Mentor

That was what I was thinking. If you are using the temperature in casual conversation and just using whole numbers then Fahrenheit would be more accurate. However I don't see much of a need for this accuracy in such circumstances.

11. Oct 15, 2012

Mentalist

Fahrenheit sounds better.

12. Oct 15, 2012

Staff: Mentor

I would rather use Kelvin.

13. Oct 15, 2012

SHISHKABOB

I like Kelvin because it's got absolute zero right at zero.

14. Oct 15, 2012

SW VandeCarr

Well my friend likes Kelvin too. An absolute scale is necessary if you're going to use temperature with other units and Kelvin is the SI unit for temperature. As I said, my friend wants only Kelvin for meteorology, but he realizes that it might be difficult for the general public to get used to hearing weather reports saying things like the high temperature for today will be 300 (K). I will say that that's never going to be mistaken for a Fahrenheit temperature in a weather report like Celsius might be (see post 1). His point is that if the US public is going to be re-educated to a new measure of temperature, it should be Kelvin, not Celsius. Otherwise, he says we might as well stick to Fahrenheit for things like weather reports, cooking and taking body temperatures.

I'm just asking for comments on this. Should the US remain practically the only country in the world that still uses Fahrenheit given Celsius arguably offers no inherent advantage but would conform to what the rest of the world is using?

Last edited: Oct 15, 2012
15. Oct 15, 2012

Staff: Mentor

I say no, but I realize that the public would most likely be overwhelmingly negative in their reaction to such a change.

16. Oct 16, 2012

SW VandeCarr

OK, but should we convert to Celsius or Kelvin? If it's Kelvin, the US would be ahead of the world instead of behind as it usually is in things like this.

17. Oct 16, 2012

Staff: Mentor

I don't think there is a "right" answer to this.

18. Oct 16, 2012

Jimmy

Recall seeing this on the forums fairly recently:

On the serious side, Kelvin doesn't seem to be a very practical scale for weather forcasts aimed at the public and conversion between Celsius and Kelvin is pretty simple. If America did officially switch to Kelvin, I'm pretty sure forecasts would still use Fahrenheit as well.

19. Oct 16, 2012

PhysicsGente

I grew up using celsius so the choice is obvious ;).

20. Oct 16, 2012

PhysicsGente

I grew up using celsius so the choice is obvious ;).

21. Oct 16, 2012

f95toli

Not true. In order to go from Kelvin to Celsius you only have to substract a number; this in turn means that Celsius and Kelvin are the "same scale" whenever you are dealing with differences in temperature. We don't actually deal with absolute temperatures that often in science and engineering, but temperature differences tend to pop up quite frequently in engineering (e.g. thermal expansion, insulation etc.) and for example chemistry. The fact that 1 degress C is the same as 1K means that all constants etc. that are part of the SI have same value in both systems.

(I work in low temperature physics,so the unit I use most is actually mK)

22. Oct 16, 2012

SW VandeCarr

I would hope everyone here knows this. For the US general public., virtually everyone has an understanding of what 81F means. When they see 27 (C) they think "cold". Obviously they could learn Celsius, but my friend thinks that as long as they do that, they should learn to think in terms of Kelvin. It's true that it's just matter of addition and subtraction, but for most people, 273 is not the easiest number to work with in your head. Also, 0 C technically should equal 273.15 K so there would be a a small inaccuracy introduced by simply adding or subtracting 273.

My friend is a research meteorologist and in his work he uses Kelvin. He doesn't want to have to work in up to three scales (four if you include Rankine).

Last edited: Oct 16, 2012
23. Oct 16, 2012

SW VandeCarr

Right. When Daniel Fahrenheit (who was Swiss) invented the more or less modern thermometer, he developed a scale that was deliberately designed for the range of human experience. Since temperatures had not been accurately measured before, he couldn't be sure what that range would be so he guessed based on temperatures normally experienced in lowland Switzerland and other parts of Western Europe. He got a scale compatible with human life over the range of 0 to 100.

Last edited: Oct 16, 2012