Not so long ago, temperature did not seem to exist, it was not measured or taken into consideration. Why was this physical size created?
How many times during the past, extremely snowy and cold winter have you listened to, looked at or searched for temperature data? If you think about it, it turns out that temperature is a physical quantity that is more often reported than all those more media-attractive, lively and “unscientific” quantities, such as the number of deaths in accidents or the price of grain on world stock exchanges. Especially when it comes to air temperature.
Information on the current air temperature is today an integral part of almost every news program, it is available in every car, on the website and on every better phone. Only data on time, hours and minutes are more widespread than data on temperature. At the same time, temperature and data about it strongly influence life. In accordance with it, daily obligations, political campaigns, military attacks, the number of purchased kilowatt-hours and the number of vehicles on the streets of the snow-covered city are planned.
But what is temperature anyway? First of all, it is not the same as heat, which is often mistakenly equated. Namely, if you ask physicists, who naturally know the most about physical quantities, they will say that temperature is an intense physical quantity. That is, it is not extensive. And it hardly means much to you at first glance. But what is it about?
Extensive quantities are, in fact, additive and proportional to the size of the physical system they describe – such are surface area and volume, density, charge, energy and momentum. If you think about it, we somehow experience this type of size more naturally and it is easier to understand – the bigger a river is, the more energy it has, or the bigger the vessel, the bigger the volume. Extensive quantities also include heat, since it is always actually some exchanged energy, while temperature, as has been said, belongs to intensive quantities.
Intense sizes, although we use them regularly as in the case of temperature, elude that kind of thinking. Often people, although they are quite close to them, do not think about such quantities at all and are not really aware of what they physically represent, so they mostly understand them conditionally, ie connect them to some very specific phenomena – the lower the temperature, the more snow. In addition to temperature, such quantities are velocity, viscosity, concentration, or specific charge.
Intensive quantities always characterize a system regardless of its size. They are such that they must be the same in the whole system and all its parts. Thus, it is understood that each part, each wagon of the train moves at a speed of 50 per hour, if it is said that the train moves at that speed.
On the other hand, when we say that the air temperature is ten degrees Celsius, we also mean that it is the temperature that refers to both the air in the room in which we read and the air that is outside. Or not? Of course not, if the room is heated. We can at least say that ten degrees is everywhere in the street. Or not either? The taxi driver measures 12 degrees on one corner of his temperature meter in the car, and the street clock with an electronic thermometer on the principle of a thermocouple on the other corner shows nine degrees. Who’s wrong here?
Are meteorologists lying when they say that the temperature in the whole city is ten degrees? Of course, they are talking about the average that refers to the conditions that prevail in the meteorological measuring station. And what if we stay in a well-heated room where we carefully and reliably measure the temperature accurately, but go further and see if the temperature is the same for every liter of air?
The fact that the temperature does not depend on the size of the system actually means something else and when we talk about it, one important thing is forgotten – it implies that the system is in the so-called thermodynamic equilibrium. When we pour hot water into a cold cup, they do not have the same temperature, but after a short time their temperature will equalize, so we believe that they are in thermodynamic equilibrium and have the same temperature that is the same for the whole system, which we said was the case. with intense sizes.
If we return, for example, with a heated room, it turns out that in that room, if we do not disturb it too much by opening and closing the windows, turning the heating on and off, after a long enough time, the mentioned thermodynamic balance will also be established. The laws of thermodynamics speak of the inevitability of that scenario. And when it already happens that the whole room is in thermal equilibrium, that all the molecules of that system are conditionally uniform in speed, then we can say that there is a size that characterizes the whole system, in whole and in parts. And that is – the temperature.
To measure it, we will insert a meter into the room and wait for it to come into thermodynamic equilibrium with the rest of the room. We consider such measuring instruments as thermometers – for historical and human reasons in general, they do not give an “intensive” number that is primarily characteristic of the speed of movement of all molecules in the room, but show a comparative, completely indirect length – the height of the mercury column. temperature higher.
Such a very suggestive meter from the 18th century conditioned the making of all previous temperature scales. All of them, whether the Fahrenheit, Celsius or Kelvin scale, are only the subject of human agreement, since the magnitude of one degree could have been set differently. As, after all, only a few centuries ago, people did not measure temperature at all, nor did they know about it.
Temperature scales are actually artificially developed in relation to two very clearly visible natural thermal phenomena that occur with water and only at normal atmospheric pressure – one is melting ice, ie converting water from solid to liquid, the other is boiling and converting water into gas. By simply choosing to have the first event at zero and the second at 100 degrees, you get the whole scale, as well as the size of each degree.
This is how, in essence, the temperature scale was set in 1742 by the Swedish astronomer Andres Celsius, although he himself chose zero to be boiling and 100 degrees freezing water. However, at the suggestion of the famous botanist Karl Line, the scale was reversed and set as it is today, when it comes to normal atmospheric pressure. It turns out that, precisely measured, the beginning and the end of the scale are not exactly zero or 100 degrees Celsius, but that does not change the essence.
Since the question of the lowest possible temperature prevailing in open space remained, in 1900 the absolute Kelvin scale was introduced, which belongs to the official SI system of measures and whose zero, 0 ° K, was moved to -273.15 ° C, which is considered the lowest temperature in nature. But the breadth of the degree is still arbitrarily human and tied to water under a certain, normal pressure.
It’s really hard to imagine what a world looked like just a few centuries ago, where temperature was neither measured nor taken into consideration, but isn’t it amazing how a completely agreed, almost imaginary quantity has become so important for everyday life today? Especially when it only indirectly speaks in what kind of thermal balance the air in the room, the human body, wood or an electronic device found itself.
However, the temperature still reveals a crucial thing about the behavior and condition of the entire system – whether it is overheated, sick, cold, mobile. Knowing only the temperature of something, we know at least half the truth about what is with it. It doesn’t matter if we are talking about the body temperature of a person who lies or the organization of a society such as a bee.