Heat and its properties

Today heat is known to be a form of energy. We receive some heat from a number of different sources. The sun, the interior of the earth, chemical action, mechanical, electrical, and nuclear energy, are the chief sources of heat. Heat is the sum of the kinetic energies of all the molecules of a body. The temperature of a body is determined by the average kinetic energy of its molecules. To measure the temperature of a body different thermometers are used. Several scales, in which the degrees are different, have been devised. The Centigrade and the Fahrenheit scales are very frequently used. On a Centigrade thermometer the freezing point of water is marked 0, while the boiling point is marked 100. On a Fahrenheit thermometer, the freezing point is marked 32, and the boiling point is marked 212. Special thermometers are constructed to show the maximum or minimum temperature for any given period. The clinical thermometer is used to find the temperature of the human body. Self-registering thermometers keep a continuous record of the temperature for any given period.

Heat can produce different effects which are more interesting and more practical importance. Solids expand when heated and contract when cooled. The increase per unit length per unit degree is called the coefficient of linear expansion. The increase in area, or the coefficient of superficial expansion, is approximately twice the linear coefficient. The increase in volume, or the coefficient of cubical expansion, is three times the linear coefficient. Liquids have a much higher coefficient of expansion than solids. A change in temperature or a change in pressure will change the volume of a gas.

How is the heat measured? We use thermometers to measure temperatures, but they cannot be used to measure heat. The measurement of a quantity of heat, however puts us to a little more trouble as there is no simple instrument which enables us to measure it directly. Quantities of heat are measured scientifically in terms of the calorie, which is defined as the heat required to raise the temperature of 1 gram of water through 1 degree Celsius. In practice it is more convenient to use a larger unit for measuring the heat energy of food. For this purpose the large calorie is used. 1 large calorie = 1000 small calories.

Ex. 1. Make the plan of the text.

Ex. 2. Put the verbs into brackets in the Passive Voice, translate the sentences.

1. We have achieved the acceleration curve in two steps. 2. Vector analysis of this kind has supported the law of momentum conservation to high accuracy. 3. This theory has shown its power in modern physics. 4. They have given a geometrical interpretation for the numbers of many groups. 5. We have known connections between arithmetic and geometry since ancient times. 6. The general theory of relativity has shown that space is not really Euclidean. 7. The mathematical formulation of the quantum theory has required the use of imaginary numbers. 8. Bertrand Russel has made fundamental contributions to mathematics.

Ex. 3. Rewrite the following sentences using: I (you, he, she, it, we, they) said, asked, etc. Translate your sentences.

1. They have dropped two objects from the top of the mast. 2. They have brought a stone from the moon. 3. He suggested a new idea but we did not accept it. 4. The

'question was unanswered. 5. They called it a "thought experiment". 6. I have read his article several times. 7. We haven't solved the problem yet. 8. Did they experiment on new materials? 9. What did you say about .their work? 10. He is holding something in his hand. 11. In what theory do the laws of motion and of gravitational force come together? 12. They agreed with each other on a lot of points. 13. The Russian cosmology helped the science to learn much new about space.