Laboratory Exercises

9. Listen and practise the pronunciation of the words end­ing with the suffixes "-tion", "-ed", "-ing": transformation, observation, foundation, motion; heated,

passed, vaporized, explained, trained, considered, supposed, placed, performed, moved; according, performing, speeding, heating, boiling, vaporizing.

10. Listen and repeat in pauses:

Heat was considered to be an invisible substance a cen­tury ago. It was called caloric. Robert Boyle and Isaac New­ton began to think about heat in terms of molecular mo­tion. Lomonosov stated that heat phenomena were due to the motion of molecules. His theory laid the foundation for the present-day molecular-kinetic theory of heat. Today heat is known to be a form of energy.

11. Listen to these questions on the above text and answer them:

I. What was heat considered to be? 2. How was it called? 3. Who stated that heat phenomena were due to the motion of molecules? 4. What is heat known to be today?

12. Ask questions using the model.

Model: Heat is known to be a form of energy.

What is heat known to be?

1. The metre is known to be a unit of length. 2. Tempera­ture is known to be the degree of hotness of an object. 3. The units of power are believed to depend on the units chosen for work and time. 4. The total amount of energy in the uni­verse is known to be constant.

13. Suggested topics for oral narration:

1. What was heat considered before Lomonosov's statement? What did Lomonosov state about heat? 2. Tell about heat as a form of energy.

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Additional Material

Read the text and describe the properties of heat and how it is measured.

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 of 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 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 trouble¹ 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 of1 gram of water through

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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.

Note

¹ puts us to a little more trouble — ставит нас в неко­торое затруднение

U NIT 9