ig8 GENERAL SCIENCE 



Since man himself does not have sufficient physical 

 power to operate large, complex machines, he has learned 

 to use the power (i) of animals, (2) of engines in which 

 the power for their operation comes from the fuel burned 

 in them, (3) of rivers and waterfalls which are made to 

 flow over water wheels and develop power to run other 

 machinery, (4) of the wind by building windmills for 

 pumping water, and even (5) the power of the rays of 

 the sun by building sun engines which transform the 

 energy of the sun's rays into mechanical energy; these 

 engines can only be run while the sun is shining, so a 

 warm country with a cloudless sky is necessary for their 

 successful operation. 



QUESTIONS AND EXERCISES 



1. What are some of the forces of nature that man has con- 

 quered ? What use does he make of them ? 



2. When and by whom were the following invented: the tele- 

 phone, telegraph, sewing machine, biplane, and steamboat ? 



3. Define energy, force, distance, work, and power. 



4. Define the units of work and the units of power. 



5. Draw the three classes of levers and name their parts. 



6. Why is it better that the long bones of our bodies are used 

 as levers of the third class ? 



7. Why do modern road-builders cut through hills and fill low 

 places ? What is a 3 per cent grade ? 



8. Does a combination of pulleys save work or waste work ? 



9. How find the advantage that the force applied has over the 

 weight being lifted by a compound machine ? 



so small that it is customary to take as the practical unit 10,000,000 ergs 

 per second. This large unit is called the watt, in honor of James Watt. 

 Since the power of dynamos and electric motors is so great, a still larger 

 unit is used to measure their power, called the kilowatt, which is equal to 

 1,000 watts. Engines are also being measured in kilowatts rather than in 

 H.P. A horse power is equivalent to 746 watts, or about three-fourths of 

 a kilowatt. 



