UNIT VI. THE RELATION OF HEAT TO HEALTH AND COMFORT 



Heat is a form of energy upon which we depend 

 for much of our everyday comfort and industry. 

 Primitive man, in all probability, had to depend en- 

 tirely upon the sun as his source of heat. When our 

 remote ancestors discovered the value of fire an im- 

 portant step toward civilization was made, as modern 

 ways of living and methods of industry require enor- 

 mous quantities of energy, most of which is obtained 

 by means of fire. 



How or when fire was discovered is not known, but 

 it is quite likely that the discovery was made in some 

 accidental way. Early man's first acquaintance with 

 fire may have been with a blazing forest set fire by 

 a flash of lightning, or perhaps with the hot ash and 

 lava erupted from volcanoes. 



The effects of the discovery of fire on man's prog- 

 ress have been great. In fact, it is difficult to conceive 

 how man could have emerged from a primitive state 

 without fire. 



There are other sources of heat besides fire which 

 are in use today. Heat is obtained by friction, from 

 other forms of chemical action than burning, and from 

 electricity. The purpose of this unit is to acquaint you 

 with the science of how heat is obtained, used, and 

 controlled in everyday. life. The use of clothing in re- 

 lation to personal warmth will also be discussed. 



How many of these things about heat do you know? 

 In your notebook answer as many of the questions 

 as you can. 



1. What do you think heat is? 



2. What happens to wood or coal when it burns? 



3. Why do people rub their hands together when 

 they are cold ? 



4. Have you ever examined an electric iron or 

 stove? What is inside of it? 



5. Have you a thermometer in your home? For 

 what is it used? 



6. How many ways do you think there are for pro- 

 ducing heat? 



7. What kind of clothing do you wear in summer? 

 In winter? How do they differ? 



8. Have you ever seen or used a thermos bottle? 

 What enables it to keep hot things hot or cold 

 things cold? 



9. What is the earth's most important source of 

 heat energy? 



10. Have you ever had occasion to remove stains 

 from your clothing? How did you do it? 



11. What kind of heating system do you have in 

 your own home? How is it operated? 



TOPIC 1. HOW HEAT IS PRODUCED 



SUGGESTED PROBLEMS AND QUESTIONS 



1. What are the sources of heat energy for the 

 earth? 



2. What are the common fuels used to supply 

 heat energy? 



3. How are the common fuels which are used to 

 supply heat energy on the earth obtained? 



SUGGESTIONS AND HELPS FOR STUDY 



1. Carefully study the problems and see if you are 

 interested in them. 



2. Plan your work throughout the unit so that you 

 bring to bear upon the solution of each problem all 

 the things you already know and new knowledge that 

 you gain from your reading and investigations. 



3. Make a thorough examination of some electric 

 heating device used in your home. 



4. The story of the formation of coal is very in- 

 teresting. Get all the information about it you can 

 from special reference books. 



5. In the study of this topic the following new 



words may be met for the first time. Study them care- 

 fully and use them frequently. 



insulator a substance which is a poor conductor of heat 

 or electricity. 



kindling temperature the temperature at which a sub- 

 stance starts burning. 



oxidation the combining of oxygen in the air with some 

 other chemical element. 



combustion rapid oxidation with the giving off of heat 

 and light. 



fuel a substance which burns readily, producing a large 

 amount of heat at a relatively low cost. 



EXPERIMENTS OR DEMONSTRATIONS WHICH WILL 

 HELP ANSWER THE PROBLEM QUESTIONS' 



Experiment 81. What is burning? 



You learned about air and burning in Unit I. This com- 

 pletion exercise is for the purpose of recalling some of the 

 important things which you learned at that time. 



Ignite a wooden splint or a piece of paper; then complete 

 the following exercise. 



When a piece of wood burns, the elements and _ 



which are a part of wood, combine with from the air 



' See workbook, p. 42. 



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