Give headings to each paragraph of the text.

Put two questions to each paragraph of the text and ask your fellow-students to answer them.

Find the infinitive constructions in the text and define them.

Give a short summary of the text.

LESSON TWELVE

THE NATURE OF HEAT

What makes one thing hot and another cold? What do the terms "hot" and "cold" really mean?

Scientists are known to have worked for a long time to find an answer to the last question. They decided at last that the manifestation of heat was caused by a weightless substance or fluid called "caloric." It seemed to be weightless because the numerous experiments proved that it did not produce any increase in weight. To explain its behaviour was simple and easy. According to the caloric theory, a hot body contains more caloric than a cold one. Hence caloric was considered to pass from the former to the latter. How­ever, experience showed that certain heat effects could not be explained by the above theory, namely: the development of heat owing to friction as well as the changes of temperature during the compression or expansion of a gas. Nevertheless, the theory in question seemed to be the only possible theory until the beginning of the 19th century, or so.

Lomonosov was the first to state that heat phenomena were due to molecular motion. His statement proved to be correct years after his death.

At present, we know heat to be a form of power. Besides, we are quite familiar with the fact that all substances are made up of little particles called molecules. These are so min­ute that a single drop of water, for example, is assumed to have millions of them. Although a drop of water left on the table may seem to be at rest, everyone of its molecules is really moving about, colliding with other, molecules, pushing them, and changing direction. Of course, while one molecule is travelling, all the other millions of molecules in the drop of water are doing the same thing. They are travelling in various directions, colliding, pushing other molecules and jumping away from each other.

What process takes place when we place a kettle full of cold water on the fire, in -other words, when we want to heat water? The molecules begin to move much faster then, so that every time there is a collision, they jump away from each other much farther than they did before. As a result, the drop of water becomes larger, that is to say, it expands. In scientific language this property is called expansion.

The much faster molecular movement makes the water first warm and then hot. On taking our kettle from the fire, we expect the molecules to slow down, and indeed the water begins to get cold. When our tea is said to be "hot" it really means that its molecules are travelling very fast. On the contrary, when the tea is cold, they are moving more slowly.

Although heat and temperature are certainly connected, it is necessary to understand the difference between them. To show that similar quantities of heat may produce very different effects in different substances, is not difficult at all. Placing a needle on the fire at the same time as a kettle of cold water, we find that the needle is red-hot before there is any marked difference in the temperature of the water.

We must say here that a red-hot needle receives far less heat than a kettle full of boiling water but its temperature is nevertheless much higher. On the other hand, if we place it in the boiling water, although the latter is certain to possess far more heat than the former, the needle gives up heat to the water and not vice versa. When two bodies at different temperatures are brought into contact, we expect the warmer body to get cold while the colder one will be warmed. In this case, heat is said to flow from one body to the other by con­duction.

As for expansion caused by heating, it is useless and even dangerous in some cases while in others we cannot do without it. For example, to measure temperature one employs a ther­mometer. In order to obtain a definite scale of temperature, we make use of the fact that bodies generally expand on being heated.

One must remember that heat may produce a change of state without changing temperature

Exercises

1. Learn the following active words and use them in the sentences of your own:

boil кипеть

caloric калория

cause (v) вызывать

collision столкновение

compression сжатие

conduction проводимость

direction направление

ex­pansion расширение

explain объяснить

friction трение

place (v) поместить

quantity

2. Translate the following sentences using the infinitive constructions:

1. Мы знаем, что теповая энергия – это энергия молекулярного движения. 2. Известно,что молекулы движутся в различных направлениях. 3. В течение долгого времени считали, что тепло – это невесомое вещество. 4. Говорят, что молекулы воды движутся быстрее, когда ее нагревают. 5. Считают, что молекулы холодного вещества движутся медленно. 6. Известно, что при нагревании тела расширяются. 7. Студенты, наверное, понимают разницу между постоянным и переменным током. 8. Нам известно, что тепло может вызывать изменение состояния вещества без изменения его температуры.

3. Find in (b) antonyms to the words in (a):

a) at rest, solid, fast, useful, charge, hot, dark, negative, the first, increase, wrong, valuable;

b) positive, right, the last, decrease, liquid, in motion, invaluable, slow, useless, discharge, cold, light

4. Find in (b) synonyms to the words in (a):

a) to employ, to make, to travel, different, like, to receive, liquid;

b) to move, similar, various, fluid, to do, to get, to use

5. Translate the following questions into English and answer them:

1. Что такое тепло? 2. Почему предполагали, что тепло - этго невесомое вещество? 3. Могли ли люди наблюдать некоторые тепловые эффекты? 4. Что происходит благодаря трению и сжатию? 5. Какие тепловые действия (phenomena) установил Ломоносов? 6. Из чего состоит вещество? 7. Как называются мельчайшие частицы вещества? 8. Что проис­ходит, когда тело нагревается? 9. Существует ли заметная разность температур между холодным и горячим телом? 10. Какой прибор используется для измерения темпера­туры?

6. Form verbs from the following nouns and use the verbs in sentences of your own:

increase, weight, statement, movement, difference, com­pression, collision, flow, application, requirement, knowledge, education, expansion

7. Translate the following sentences paying special attention to the words in bold type:

1. The static charges are known to be at rest. 2. The alter­nating current changes its direction many times a second. 3.We know the electric charges to be positive and negative. 4.Some liquids are known to conduct current without any changes to themselves. 5. On the contrary the electrolytes are known to change greatly when the current flows through them. 6. One can charge dissimilar objects by rubbing them.