What is Heat?

When heat, a form of energy, is supplied to a substance, we expect it to produce a rise of temperature. In other words, heat usually causes an increase in the average kinetic energy of the random motion of the molecules of which the substance is made up. However, heat may also produce a change of state without any temperature change.

Today heat is known to be a form of energy. But about a century ago heat was considered to be a kind of a weightless substance which was neither created, nor destroyed. This substance called "caloric" was believed to pass from a hotter body to a colder one, eventually both of them coming to the same temperature. To explain that phenomenon was easy: a hot body, it was supposed, contains more of the heat fluid, i.e. caloric, than a cold one; and this fluid flows from hot to cold. Again, people knew that it takes more caloric to raise the temperature of a pound of water 10⁰ than a pound of iron. They naturally supposed water to have higher caloric content than the iron. In fact, the caloric theory of heat as it was called accounted for almost everything that was known about heat at that time, except one important phenomenon, namely: the production of heat due to friction. However, numerous laboratory experiments demonstrated that each time when mechanical energy was expended as a result of friction, a corresponding amount of heat was produced.

In spite of that inability to explain the production of heat by friction, the caloric theory of heat seemed to be the only acceptable theory.

Great scientist and poet Lomonosov was among the first to find and state that heat phenomena were due to the motion of molecules. That statement of his resulted from many carefully performed laboratory experiments, from study and observation.

Lomonosov's theory laid the foundation for the present day molecular-kinetic theory of heat. As was often the case he left his contemporaries far behind and his statement was finally proved long after his death. The caloric theory of heat is known to have existed almost up to the middle of the 19th century.

The unit of heat is called a therm or a calorie; the latter term appears to come from the Latin word "calor" which means heat.

A calorie is defined as the amount of heat required at a pressure of one atmosphere to raise the temperature of one gram of water one degree Centigrade. (We know the gram to be a metric weight equal to 15.432 grains of the English system of weights).

One should not think that the very amount of heat which will raise the temperature of one gram of water from 0 to 1⁰ C will also raise the temperature of the same mass of water from, say, 60 to 61⁰ C. Experiments have shown that the quantities of heat to be required in these two cases are slightly different. Hence, the true calorie is defined as that quantity of heat which will raise the temperature of 1 gr of water from 19.5 to 20.5⁰C.

Exercise 2. Read the following words. Translate them.

kinetic, molecule, i.e., pound, iron, mechanical, inability, contemporary, finally, phenomenon, century, raise, experiment, require, define, theory, weight, amount, case, suppose, fluid, friction, average, increase, iron, scientist, numerous, content.

Exercise 3. Translate the words into English:

період, вага, речовина, рух, доводити, проте, озеро, внутрішній, рідина, пояснювати, руйнувати, середній, визначати, перетворювати.

Exercise 4. Answer the questions:

1. What is heat?

2. What does heat usually cause?

3. What is a substance made up of?

4. Does heat always produce a change of temperature?

5. Was heat considered to be a form of energy a century ago?

6. What did Lomonosov state?

7. Who was among the first to state that heat phenomena were due to the motion of molecules?

8. How long did the caloric theory exist?

9. What is the unit of heat?

10. How is the caloric defined?

Exercise 5. Give the synonyms to the words:

increase, suppose, know, call, heat, great.

Exercise 6. Give the antonyms to the words:

The first, motion, carefully, fluid, heat, present-day, raise

Exercise 7. State if the following sentences are true to the fact or false. Correct false statements.

1. Today heat is known to be a form of energy.

2. Heat usually causes a decrease in the average kinetic energy of the random motion of molecules.

3. The substance called „caloric” was believed to pass from a colder body to a hotter one.

4. A hot body contains more of the heat fluid than a cold one.

5. The caloric theory of heat accounted for almost everything that was known about heat.

6. Great scientist Lobachevskiy was among the first to find and state that heat phenomena were due to the motion of molecules.

7. Lobachevsiy’s theory laid the foundation for the present-day molecular-kinetic theory at heat.

8. The true calorie is defined as that quantity of heat which will raise the temperature of 1gram of water from 19.5 to 20.5 C.

Exercise 8. Write out the keywords and phrases and make up a plan.

Exercise 9. Retell the text.