How cold will it be tomorrow?

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This topic contains 19 replies, has 13 voices, and was last updated by  Simon Paynton 3 years, 6 months ago.

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    What temperature will it be tomorrow if it will be twice as cold as today, if today’s temperature is 0?



    What is the Temperature Scale? Celsius or Fahrenheit? Does it matter?


    Simon Mathews

    I agree with umar, the scale is important. Temperature scales other than Kelvin are just arbitrary convienences for the range of temperatures we are interested in. If it is 0 Kelvin it is not possible to be twice as cold as that.



    Let’s say it is 0°F (-17.7°C or 255.2°K)

    Half as cold would be:

    -229.4°F (-145.2°C or 127.8°K)


    Unseen is American and so the F scale was there for those from the only two countries who still use it (the USA and the Bahamas). For everyone else in the standardised measurements compromising world…we can try 0°C (32°F or 273°K)

    Half as cold would be:

    -137.5°C (-215.5°F or 135.5°K)

    And now kelvin. 0°K is -273°C or -459.4°F

    Divide absolute zero by 2 two and you end up with

    0°K is -273°C or -459.4°F

    No change it seems ? None of us would be alive in any case.

    Countries that use °F

    • This reply was modified 5 years, 9 months ago by  Davis.


    This shows countries that still use miles (there are a handful more than with °F (to be fair many in the UK still use the term miles and most British and English speaking Canadians measure personal body height in feet and personal weight in pounds).



    Twice as cold is a meaningless question as theres no such thing as cold. Only an absence of heat. Your question would be better asked what would tomorrow’s temperature be if it is half as warm as 0 degrees.

    Although this question has its own issues, as others have pointed out: to answer this question, one needs to know the scale. Since no scale is given, I feel that kelvins is the scale to be used as it is most typically used in science. In which case: 0/2=0



    Heat is simply the average kinetic energy of the molecules of the substance. OK, or -459F or -273C (I dropped fractions because I don’t remember them) is the temperature where the kinetic energy is zero, of course you can’t get less than that.

    Because only kelvins shows a linear relationship between heat and the number on the scale, it’s preferred by physicists; many formulae have “temperature” as a variable and it needs to be absolute, just like distances, etc., are, with zero being the lowest possible value. Celsius or fahrenheit are more useful in a day to day context becuase the numbers are reasonably small for temperatures we are likely to run into in our daily lives. (Fahrenheit, in fact, was originally designed so that weather would be in the range 0-100, but of course there’s plenty of weather outside that range.)

    Given that zero is in different places on all three scales, as pointed out, it’s important to know the scale when presented with a question like Unseen’s.



    As @matt describes, there’s no such thing as “cold”. However, our perception of cold is dependent on rate of heat loss (particularly to our skin surface). That heat loss is dependent on a number of things, but for the purposes of the question let’s assume we’re standing, our skin’s moisture and the air’s humidity remain constant, the wind is zero, and the sky is cloudy with a low cloud deck, like a northern winter’s day.

    In that case, the rate of heat loss will be largely dependent on thermal radiation, which goes as the 4th power of the temperature difference. So for the rate of heat loss to double (twice as cold), the temperature difference required is not enormous. A quick calculation puts it at -44.5C, assuming we were using Celsius for the scale and body temperature for our reference. Seventy five below if everything is in Fahrenheit.



    @steveinco You know kelvins have the same scale as celcius, right? Like the difference between any two degrees is the same for both kelvins and celcius. 0K = -273C and equivalently 273K = 0C.

    Good thinking with the rate of heat loss @drbob



    @matt, yes I do.

    That makes it simple to convert between the two.

    Converting from Fahrenheit to Celsius is much more complicated because not only are the zero points different, the size of the degree is, as well.

    There is (was, really) a scale starting at absolute zero but sized in Fahrenheit degrees (where the difference between freezing and boiling is 180 units, rather than a hundred), it was called the Rankine scale. Freezing was 491.67 on that scale.



    Although this question has its own issues, as others have pointed out: to answer this question, one needs to know the scale.

    You also need to know something else about the question. As some have pointed out, coldness is also a perception. So one way of interpreting the question could be “Under what conditions would it be perceived as twice as cold tomorrow as it is today,” which makes it a question about wind the wind chill phenomenon.



    Silly People, 2 * cold = hot/2. And tomorrow = 1/7 week bigger.


    What University did Kelvin attend to get so many degrees?



    @reg Silly man. Kelvin was so chilled he didn’t need a uni


    Simon Paynton

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