286 PHYSICAL LIMITATIONS HAVE BEEN OVERCOME 18. Why is there a possibility of condensation of moisture between the walls of air-conditioned houses? 19. Why would it be necessary to decrease the humidity in the air if it were fairly high when using radiant cooling-panels? 20. Why is it possible to obtain five times as much heat from electricity by using it to operate a compressor, rather than by using it in a direct-heating device? Is any heat wasted in an electrical heating device? 21. Discuss the various methods of removing dirt from the air. 22. If you were allergic to pollens, what method of removing pollens from the air would you select, and why?
UNIT V MAN HAS DISCOVERED AND HARNESSED DIFFERENT FORMS OF ENERGY INTRODUCTION TO UNIT V Today every man, woman, and child in the United States has, on the average, more than ten slaves to work for him. These mechanical slaves, operated by the energy which man has learned to harness, are equivalent to ten man-power units of work per person in the United States. This situation is not true throughout the world, for the 127 million people in the United States accomplish as much mechanical work aided by power machinery as the rest of the 1875 million people on the earth. A one-horsepower motor can do the work of ten or more average laborers for only a few cents a day. It has been calculated that the average American family employs the equivalent of fifteen able-bodied men for forty hours a week, at the total cost of about $75 per year. It is through the labor of these mechanical slaves that modern man is acquiring more and more leisure time and more and more timesaving devices. These slaves transport him from place to place with ever increasing speed; they dig his ditches, till his soil, reap his crops, prepare his foods, and make his clothes. These developments have made modern life more complex, because man has to control these machines. As he gains more and more power, it becomes more important that he should determine what to do with it. Shall he use it for war or peace? Shall he use it for exploitation or for the betterment of his fellow-men? What will modern man do with his leisure time? Will it contribute to a more ideal life on earth or not? These problems did not exist for any man two hundred years ago. His main problems were the elemental problems of securing food and clothing sufficient to keep himself and his family alive. In past ages, human slavery was common, and even today a few people and nations can gain power, luxury, and leisure by this ex- 287