Man's physical universe

xanabras

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.

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