294 FORMS OF ENERGY for nothing." It is the law of conservation of energy. A more technical statement of the first law of thermodynamics is that in the transformation of work into other forms of energy and in all energy transformations there is no gain or loss of energy. No scientist would ever consider any scheme that involved "getting something for nothing." Many inventors, unaware of this fundamental principle, have attempted to devise perpetual-motion machines; and the average person would not be greatly surprised to see one in operation, although he would be attracted by the novelty of it. perpetual-motion machine is a machine that would do work indefinitely without the expenditure of energy. The first law is based in part on man's consistent failure to construct a perpetual-motion machine. A machine that would continue to move indefinitely without doing work is impossible, because a perfectly frictionless machine cannot be built and friction always decreases the mechanical energy with the formation of heat. The Second Law of Thermodynamics. The second law of thermodynamics, stated non-technically, is: "Everything in the universe tends to run down." A clock always runs down. Water runs downhill and never up, unless an outside force is brought into play. A bullet gradually loses speed and never gains speed after it has been fired. A human being grows old but never grows younger physically. People who realize the significance of this law would seek help from sources of power greater than they possess. They would seek to associate with people of greater ability and development if they really wanted to grow themselves. Gilbert N. Lewis expressed the statistical nature of the second law of thermodynamics when he stated, "Stripped of its finery we find that the second law states that if a pack of cards is thrown into a shufifling machine the chances are that it will become shuffled." The thought that Mr. Lewis thus expressed is that any system left to itself approaches a definite state of equilibrium. This law implies that the universe is running down and will eventually come to a dead stop, but some people believe that additional knowledge will show that the universe is not running down. At present there is nothing that we can do about this problem; and it is unimportant anyhow, so we will not pursue it further. Technically, the second law of thermodynamics states that heat energy tenuis to flow from a higher to a lower temperature and will not flow by itself from a lower to a higher temperature. In other words, heat, just as water, does not flow uphill. The consequences of thermodynamical reasoning have not only enabled the engineer to design more efficient heat engines, but they A
ENERGY MANIFESTS ITSELF IN MANY FORMS 295 have aided progress in many branches of physical science, ranging from atomic structures to weather-forecasting. To transform heat into work, heat engines are employed. All heat engines utilize the energy of expansion of gas as it does work in overcoming the force opposing this expansion. The efficiency of heat engines becomes greater the greater the temperature drop. This conclusion, based on the second law of thermodynamics, has led to the use of superheated steam in boilers at extremely high pressures. Boilers built to withstand these very high pressures are much more efficient than the lower-pressure boilers. As a result of the application of this principle, railroads have greatly increased the efficiency of their locomotives. Higher efficiency cannot be obtained practically by lowering the final temperature in a heat engine because it requires the expenditure of energy in refrigeration to lower the temperature below that of the atmosphere or the nearest large body of water. Increasing the pressure in steam boilers produces higher initial temperatures, but the increase in efficiency thus made possible is obtained only at the expense of using very strong materials to withstand the high pressures produced. Mercury has been used to replace water in a few installations because it has a higher boiling-point than water and thus makes it possible to produce higher temperatures without such correspondingly high pressures. Unfortunately, mercury is quite expensive, and its vapor is very poisonous to breathe. Dowtherm, a mixture of diphenyl and diphenyl oxide, manufactured by the Dow Chemical Company, is now replacing water in some boilers because it boils at 500° F., as compared with 212° F., the boiling-point of water. only 53 pounds per square inch, Dowtherm vapor at 650° F. has a pressure of square inch for steam at the same temperature. as compared with 2200 pounds per STUDY QUESTIONS 1. How many mechanical slaves per person are there in the United States today? How many of them do you think have been unemployed? Why? 2. Why is it that modern man has more leisure time? 3. What important problem has man's machines presented to him? 4. Define energy and work. 5. State the law of conservation of matter. 6. What is the most convenient form of energy to measure? 7. List all the forms of energy that you can think of. 8. Describe all the energy transformations that may be observed in your own home.