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What really "is" temperature? What does it mean when the radio says it's 78 degrees and a fine warm day? And for that matter, how is "temperature" related to "heat"? First, let's review the temperature scale. Strangly enough it's easier to explain how the temperature scale came to be, before going on to discuss what temperature "is".What we all do know is things like fire is "hot" and ice is "cold", even if we can't easily explain why, and there are intermediate states between the "cold" of ice and the "hot" of fire which we can readily distinguish and might call "warm" or "very warm" and so on. This probably doesn't seem like much but it is actually pretty important. Scientists a few hundred years ago were struggling with the whole concept of what we now call temperature, and it took a pretty smart person to find a starting point. Isaac Newton (around 1700) was a pretty smart man, famous for a whole range of new ideas including calculus and gravity, and he applied his genius to many different problems, including the concept of temperature. Lacking any better idea Newton started ranking things in order, from the coldest to the hottest, using the intuitive idea we all have for "hotness", ie hot things burn your fingers. After a bit of work Newton had a list of about 20 items that started with "cold air in winter" and finished with "glowing coals in the kitchen fire". Each item in his list was "hotter" than the one before it. Newton could now say "how hot" something not on his list was simply by saying "as hot as my body" or "as hot as boiling water" or "in between my body and boiling water", and so this list was a perfectly useable temperature scale that allowed him to describe the temperature of something to someone else as long as they both agreed on what the list of standard temperatures was. The concept of temperature, and the word for it, still hadn't been invented so Newton described the "hotness" of something as the "degree of its heat". Of course with only about 20 points his scale was a bit crude and not very convenient, so he set about finding some simple system that could be used to measure the "degree of heat" of an object. The fact that most things expand as they get hot was well known, and so Newton took a container of linseed oil and measured its change of volume when it was placed up against "cold" and "hot" objects. He found that a container sitting in melting snow and holding a volume of 1 litre of linseed oil contained a volume of 1.0725 litres when placed in boiling water. After playing around with the numbers a bit he decided to set "degrees of heat" proportional to the change in volume of the oil, and defined "0 degrees of heat" as the volume corresponding to melting snow, and "33 degrees of heat" as the volume corresponding to boiling water. With some quite ingenoous experiments he was able to show that the "degrees of heat" measured by the volume of the oil corresponded quite well to the sequence of "hotness" indicated by his previous list, and so he concluded his new instrument was a useful way of measuring what we now call temperature. Just why he chose 33 "linseed oil" degrees for boiling water isn't clear, but that's what he did, and he called the instrument he had developed a "thermometer". |
fire is hot
ice is cold
and our coffee is warm
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more coming later...