Why is the absolute scale adopted by System International
Answers
Answer:
so we can no other systems of communication
I presume you are referring to the use of degrees Kelvin in, for example, chemistry, rather than Celsius or Fahrenheit.
Any temperature scale requires two decisions:
Where you measure from , i.e. what your zero point is.
What is the division between points on the scale, i.e. how large is a degree on the scale.
Both of these decisions are essentially arbitrary (more on this in a moment) but as long as you have fixed both of these things, then anyone can use them and understand them.
Celsius is probably easier to understand. The zero point is defined as the temperature at which water freezes. The temperature at which water boils is defined as 100° so you simply divide this range into 100 and you have the definition of 1° Celsius. It’s been refined and is a bit more precisely scientific defined now, but that is essentially where it came from.
Daniel Fahrenheit’s thinking is a bit more complex and not precisely known, but he used the freezing point of a certain brine solution as his 0° and probably the human body temperature as 100° (adjusted later to 96°) hence the temperature at which pure water freezes is 32° and the boiling point of water works out at 212°- it’s a bit more complicated.
If you work it out, degrees F are smaller than degrees C but as I mentioned these are arbitrary divisions and in fact I could define the freezing point of water to be 50°H, the boiling point of water to be 200°H (Hawley) and it would be a perfectly usable temperature scale. Nobody but me would use it, but there’s nothing wrong with it.
Science for many years has used the Celsius scale, (even within the USA), to denote temperature. For most purposes this is fine, such as saying that lead melts at 327°C and everyone will understand what you mean. It’s just using the number to mark a point. However, this doesn’t work very well in certain chemical calculations, for example.
To understand why, you need to understand what the temperature of something actually means. In fact it is a measure of the energy possessed by the molecules or atoms of a substance. Something like vibration is the best way to put it. The atoms of a red hot iron bar are vibrating a lot, but those of such a bar in the freezer aren’t vibrating much.
You might well ask, “what if the atoms aren’t vibrating at all” - that is they possess no energy. Scientists are ahead of you here - they worked it out that the point at which there is no thermal vibration is at a temperature of about -273°C. It’s referred to as absolute zero.
However, when you’re working out how quickly a chemical reaction is going to take place then it turns out that it’s proportional to the overall energy of the atom or molecule. More energetic ones react faster. The absolute temperature scale is pretty much a direct measure of this. Celsius and Fahrenheit are not, because their zero point is fixed to a temperature where the atoms still have a lot of energy. If you raise the temperature of some atoms from 10°C to 20°C you have not doubled the energy of the atoms. They already had quite a lot at 0°C
Absolute zero means that the atoms have no energy of this kind. It’s a natural zero point and not arbitrary, so all we need to do is decide on the size of one degree and we have our scale. As the Celsius scale was by far the most popular in Science they just used this, and named it after the famous scientist, Lord Kelvin. So a degree K is the same size as a degree C - it’s just the zero point is different.
If you then do your calculations using °K, you can use the number directly in the calculation, but if you used °C or °F you’d have a more complex equation and the calculation would be harder (and more error-prone), that’s why the absolute scale is used much of the time. I used to do this as a job and it made my life a lot easier.
Chemists and such like will realize that I’ve simplified things a bit here, ignoring atmospheric pressure and such like, but fundamentally it’s all about the amount of energy.