Temperature scales

[matt_london]

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Say for example today was 32'farenhieght and tomorrow it was 64' farenheight would it feel twice as warm? If you convert these temperatures to Celsius it would be 0c on day 1 and 16c on day which is not double the temp so I would assume the answer is no. But neither is it 16 times warmer�? Is this because the scales do not start at 0 but at minus figures? You would not believe the things that keep me up at night��

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[Loosehead]

Twice as warm as what? you need a common frame of reference.

[gen2]

Your relative proportions will only work if you use the absolute temperature scale called Kelvin. Zero degrees Celsius is approx 273 K. An object would be twice as hot if its temperate went up to 546 K (273 degrees Celsius)

You have to watch out for these erroneous comparisons in everyday life. For example If newspaper A sells 1 million copies and newspaper B selld 3/4 million copies then a true comparison can only be made if the scale starts at 0 (ie A sells 33.3% more papers than B). Now the sneaky newspaper in question shows the sales as a bar chart that starts at 1/2 million so at a glance it appears that A sells twice as many copies as B!

[JudgeJ]

The Fahrenheit and Centigrade (or Celsius) scales are arbitrary, comparative scales. Your idea that something would be “twice as warm” falls down immediately because something which is 20 degrees Centigrade would be 40 degrees Centigrade to be “twice as hot” – an increase of 100%. If you take the same measurements in Fahrenheit it would be 68 degrees and 104 degrees – an increase of only 52%. The two scales only coincide at minus 40 degrees.

The Centigrade scale was devised with 100 degrees between the freezing point and boiling point of water. It is somewhat more logical than the Fahrenheit scale. Zero degrees (i.e 32 degrees F below the freezing point of water) on that scale was chosen as it was believed at the time that nothing could exist at a lower temperature. It was also believed at the time that on the Fahrenheit scale normal human blood temperature would be 100 degrees. The fact that it is actually 98.4 is said to be because the person on whom Mr Fahrenheit based his measurement had a fever at the time!

As gen2 says, The Kelvin or absolute scale is the only one where a comparison such as yours would be valid. This is because it is an absolute measurement energy contained within the object.

[brachiopod]

As gen2 says, it will only work on temperature scales based on absolute zero (it doesn't have to be the Kelvin scale which is based on the Celsius scale in terms of its intervals).

The Celsius and Farenheit scales are arbitrary in terms of the interval and the starting point (ie zero). So any comparisons such as "twice as hot" are meaningless.

Anders Celsius chose the freezing point of water for his zero, and divided up the difference between this and the boiling point into a convenient 100 units (hence why it was sometimes referred to as the 'Centigrade' scale). If you like, it was a 'metric' scale.

For his scale, Gabriel Farenheit used a mixture of ice and salt (known as a 'freezing mixture') for his zero point (the coldest temperature that could be created in a lab at the time), and human body temperature for his second reference point. Originally, the difference between these two temperatures was divided arbitrarily into 12 (why not? There are 12 inches in a foot), then a little later, into 96 (a multiple of 12).

It all depends where you start your scale and what measure of thermal energy (which is an absolute measure) is represented by each graduation on that scale.

[brachiopod]

Sorry, JudgeJ, it took so long between typing and submitting my last answer that it appears that I have just rehashed your answer ! It was not the case !

Unfortunately, I was distracted and actually had to do some work inbetween (how inconsiderate eh? First day back aswell.....!!)