There Does Heat Hide?
The Ghost of Warmth
The first theory (or rather, hypothesis) was that heat or warmth is a special substance capable of penetrating into any body. This substance was called “caloric” and was considered weightless and diffused throughout the matter, capable of “combining” with bodies, turning solid bodies into liquids and liquids into gases. According to this reasoning, the more caloric in the body, the higher its temperature. The idea that heat is a substance that is not generated or destroyed, but only redistributed between bodies, was expressed back in 1613 by the great Galileo Galilei.
Scientists of that time, when endeavouring to prove the existence of caloric, relied on the facts obtained by experience.
So, they saw two bodies — one cold and one hot — and observed that when they came into contact, the hot body would cool and the cold one would heat up. Indeed, it looked as if something was pouring from a warmer body into a colder one. It was believed that every body consists of two substances — the substance of the body itself (water, copper, iron, glass) and caloric. At that time, even equalities of this type were written:
Opponents of the Caloric theory
disproved it through other experiments.
Everyone knows that when heated, bodies increase in volume, or expand. Supporters of the theory argued that this was due to the presence of caloric in the heated body.
Opponents also cited the example of water, which behaves differently when frozen.
Water, as you know, expands when cooled (put a full bottle of warm water in the freezer and see what happens), although logically, when cooling, the caloric should leave it and the frozen water should have a smaller volume.
WATER + CALORIC = WATER VAPOUR
ICE + CALORIC = WATER
Movement is Life!
Thus, another theory (hypothesis) was proposed at the beginning of the 17th century by English scientist Francis Bacon.
According to this theory, heat is the movement of small particles (molecules, atoms) inside a body. This hypothesis was also based on experimental observations demonstrating that heating can be caused by movement. For example, scientists drew attention to a fact known to any blacksmith for a long time: under repeated blows from a hammer, a cold piece of iron becomes hot.
In addition, the method of obtaining fire by friction has been known since time immemorial. Experiments showing that two pieces of ice or fat or wax can be melted by simple friction against each other, without touching any warmer body, cast doubt on the existence of caloric. It turned out that, with strokes and friction, you can produce heat yourself, without getting it from
another source. Such views on the nature of heat are called the mechanical theory of heat. This theory had many famous supporters — including Descartes, Boyle,
Hooke, and Lomonosov.
In 1760, the Scottish physicist and physician Joseph Black conducted another experiment: he applied the same amount of heat to equal masses of various sub-
stances and found that the bodies were heated differently. He did not find any caloric, but thanks to Black and these experiments, we now know that different substances have different thermal capacities and that this process has nothing to do with caloric.
Both theories, with all their differences, had something in common. Both of them believed that warmth is something contained within a body.
According to the first hypothesis, the body contains caloric, and in the second, particles with their “life force” (this was what they called kinetic energy). They also agreed that heat does not simply appear and disappear: if, on contact between two bodies, one of them loses heat, the other receives it. What is lost by one body is acquired by another. What ended the dispute about the nature of heat? Which of the two hypotheses won? It should be noted that the experiments and studies in the 18th century could not
close the case. More complex experiments were still needed, which would show that a body’s temperature can rise without any supply of heat, due to mechanical work alone. So at the end of the 18th century, the experiments of Anglo-American Sir Benjamin Thompson (Count Rumford) did some tangible blow to the caloric theory Rumford was drilling out gun barrels in his workshop when he noticed that the temperature of the drill and cannon barrel had both greatly increased. Then, Rumford decided to conduct an experiment: in a metal disc, which he placed under water, a hole was drilled with the help of a blunt drill, driven by the force of two horses. After two and a half hours, the water boiled. “The astonishment of others who saw that such
a mass of water boils without fire was indescribable” Rumford recalled. From his experiments, he concluded that there is no caloric, and that movement is the cause of heat.
In this way, famous scientists of that time were able to refute caloric theory through ingenious experiments, proving that heat is weightless and can be obtained in any quantity simply through mechanical movement, or, in other words, by doing work. In addition, by the middle of the 19th century, atomism (philosophical doctrine on the intermittent structure of matter and small particles — atoms and molecules) stepped forward in this direction. Physicists, relying on this science, could now explain the essence and nature of heat.
As a result, scientists came to the con-clusion that:
- Caloric does not exist.
- Heat is caused by the movement of particles within bodies
The Energy Inside Us
It is known that all bodies consist of molecules that are in continuous motion.
This means that these molecules have kinetic energy
. In addition, in solid bodies and liquids, each molecule also possesses potential energy, since it is connected with the surrounding molecules by forces of interaction.
And so: what is “contained” inside a body is not heat, but the internal energy of the body(that is, the sum of the kinetic energy of all of the molecules and atoms of the body and the potential energy of their interaction).
Heat is a part of the internal energy of the body which is transferred (for example, upon contact) to another body or other bodies.
Each of you is unknowingly a source of heat, or rather, a “producer.” When you are engaged in sports, actively moving, running or riding a bicycle, you get hot. Your face may turn red, your temperature may rise
slightly, and you begin to sweat. This is not due to the fact that heat began to fl ow into your body, but simply because your body is doing work and the molecules that make up your body begin to move faster. This increases the internal energy of your body.
We, imperceptibly, have reached the concept of internal body energy — one of the most important principles of a great area of physics called thermodynamics.
In another article, we will tell you more about what the internal energy of our body is, how it changes, and how these changes can be used in everyday