246 Introduction to the Study of Science 



work performed by a machine is never greater than the amount 

 of energy supplied or put into it, that is, it cannot be more than 

 100 per cent efficient. Do these propositions state different 

 facts or the same fact in different ways ? If this is the correct 

 view of the world of energy and of the purpose and efficiency of 

 machines, can a plan to invent a machine that will create energy 

 be sane ? Is perpetual motion possible ? Explain. 



Exercise: Horse power and efficiency. 1. A stream flow of 400 

 cubic feet a second has a head of 35 feet. What is the total amount 

 of energy of the water per minute, expressed in foot-pounds? At 

 what rate is the energy available, expressed in horse power? 



2. A horse power is equal to 746 watts ; and 1000 watts equal one 

 kilowatt; or a kilowatt is equal to about one and one third horse 

 power. How many kilowatts of electricity will the above determined 

 horse power develop ? 



3. The Keokuk power plant produces 300,000 horse power. How 

 many kilowatts will this equal? 



4. Suppose the ascertained horse power of Problem 1 were uti- 

 lized in water turbines of 90 per cent efficiency. What would be the 

 amount of horse power delivered ? 



5. A Pelton wheel delivers 1100 horse power of useful work out of 

 a total 1500 horse power input of energy. What is the efficiency of 

 the wheel? 



6. A machine delivers in useful work 18 per cent of a total input 

 of 560,000 foot-pounds of energy a second. What is the horse power 

 delivered? What is the horse power of the energy supplied? 



102. Water power and transmission of energy. The revival 

 of the use of water-power has been largely dependent upon 

 progress in invention of machinery for the production and 

 control of electrical energy. As long as the use of power was 

 restricted to the immediate vicinity of its production, the use 

 of falling water was necessarily limited to a few localities: 

 Water for power purposes is not often available where the power 

 is needed. Consequently other sources of energy, such as fuel 

 for steam and later for. internal combustion engines, had to 

 be utilized. Meanwhile men learned to produce electrical 

 energy economically, to transmit it over long distances, and to 



