General question about temperature

[bloodhound]

this has been troubling me for a while....

 

if its 0 degree centrigrade,, and the weather forecast says it will be twice as cold tomorrow, then how cold will it be?

[Martin]

this has been troubling me for a while....

 

if its 0 degree centrigrade' date=', and the weather forecast says it will be twice as cold tomorrow, then how cold will it be?[/quote']

 

scaling by proportions like that always assumes some zero or origin to the scale.

 

where I live the weather forecaster would never say something like "twice as cold"

because that wouldnt make any sense to the people listening

 

it is a wacky question, so you can get various wacky answers

depending one what people assume for the implied zero

 

IF THE IMPLIED ZERO IS 0 C, THEN twice that is 0 C and half that is 0C, so the weather forecast means that the temp will not change.

 

IF THE IMPLIED ZERO IS 0 K, then we are on the absolute scale

and then "0 celsius" is really 273 K

and then "twice as hot" would be 546 K

and "half as hot" or "twice as cold" would be 136.5 K.

 

that sounds more like the South pole of Mars

but I think they do not have a radio weather report there

[bloodhound]

its not that weather forecasters use that phrase here.. i just wanted to know..... thanks for the answer

[Martin]

its not that weather forecasters use that phrase here.. i just wanted to know..... thanks for the answer

 

glad they dont

but if people actually did use Kelvin then it would make sense

 

I like this line of questioning.

 

if you use an absolute scale then----well you know how hot things glow?----if you make something TWICE AS HOT then it will glow SIXTEEN TIMES AS BRIGHT

 

and if you make it 3 times as hot it will glow 81 times as bright

 

 

that is, if you double the Kelvin then it will increase the

watts radiated per sq. meter of surface area

by a factor of 16.

 

this is called the Fourth-power Law and one of the neatest things in the second semester of college general physics

 

 

since that law is so neat we should probably all be speaking of temp with an absolute scale like kelvin

and then phrases like "twice as hot" would make clear sense

[5614]

similaryly its like if you say its -2C outside but its gonna be twice as hot tomorrow... but one sec; -2 * 2 = -4 and thats colder!!!

 

and youre not gonna say its squared as hot tomorrow! (and that'd only work with 2).

 

again as soon as you hit zero and negative numbers you run into problems which is one of the advantages of kelvin.

[YT2095]

take a look here, from post #30 onwards:

 

http://www.scienceforums.net/forums/showthread.php?t=2164&page=1&pp=50