If 100°C is equal to 212°F then why is 1°C not equal to (212/100) or 2.12°F but instead equal to 33.8°F?
In: 0
Hey. Suppose you want to know how long is a thing. What you will do? You will find something straight, better if it is a ruler. Something straight with a length. That will be your *standard*.
You see, measuring the length of a thing is essentially comparing the measured thing with the standard. You may say a tree is roughly three times as high as you. Your height is the standard. If you think it is too sloppy, you will divide your standard into equal, smaller lengths. Now you can do a *finer* measurement. That is the *scale* on your standard. And this is how a ruler is made.
It is the same logic for measuring temperature. You need *two points* of temperature for an abstract “length”. That will be your standard to compare. And you divide your standard into equal, smaller parts.
Now you want to compare two rulers with two different scales. You need a common length enclaved on the two rulers, then you aligned the rulers with two endpoints of the common length. Only by then can you compare the length of the finer scales. You will not find the common length by a single point, there must be two points, right?
You may frown. Okay, we talk about the case directly. In the two temperature “rulers”, the 0°C is aligned with 32°F and the 100°C is aligned with 212°F. So the common “length” on the °C ruler is 100°C. But on the °F ruler, it is (212-32)=180°F. Thus the “length” of 1°C is 9/5°F and 1°F is 5/9°F.
There was extra trouble the past people made. Measuring temperature is something different from measuring length. When you use rulers, the usually used point with a “0” mark is your *reference point*. And you usually use the point to align one end of the measured thing. You will not causally put the point anywhere. But in temperature systems, the reference point can be aligned with any possible temperature. 0°C is not 0°F, but 32°F. 0°F is not 0°C, but -17.78°C. Hence it does not make sense to say directly “1°C = 9/5°F” because their reference points are not aligned with one temperature in reality.
The story ends here. Ah, no. I lied. Measure temperature as length is not “abstract” at all. We measured some length for it before. That was how (one kind of) thermometer works before!
They put some liquid into a glass tube. If it is hotter, the liquid will expanse and climb up in the tube. If it is colder, the liquid will contract and fall along the tube. As long as the liquid moves at a uniform speed for your stable heat source, that system will be a good thermometer. We just needed to measure the height of the liquid in the tube. Decades ago, this kind of thermometer (with mercury in the glass) was still quite common.
The Swedish astronomer Anders Celsius used the freezing point of the water as the reference point and the boiling point as the other point. Because he used water for his thermometer (If I am not wrong). And he subdivided the height difference into 100 parts. The two temperature points are exactly the points his thermometer fails. Since he used water, Celsius’s thermometer could not be sealed, that would be too dangerous. Vapors will explode. However, the speed of water flowing in the tube was thus quite sensitive to the air’s pressure.
The later German physicist Daniel Gabriel Fahrenheit had another idea. He made the mercury thermometer. It could be sealed, worked well, and could measure a wide range of temperatures. But the points he used for his standard were (1) the freezing point of a kind of salt solution (as the reference point) and (2) the average human body temperature at that time. And he subdivided the height difference into 90 parts. He did this for commercial considerations; the standard points he used were also quite useful in his age and he had the finest scale among different scales used at the day. He made his success once, but that becomes a troublesome legacy.
Latest Answers