PAET III. WORK, ENERGY, AND 

 ELECTRICITY 



CHAPTER XV 

 COMMON TYPES OF WORK 



185. Questions for Discussion. 1. When a mountain stream wears 

 away the stone and soil and carries tbem to a valley where they are 

 deposited, is work being done? May work be considered as construc- 

 tive or destructive, wasteful or useful? 2. Why is it desirable, in using 

 any kind of machine, to decrease the amount of friction? Why do 

 we oil a bicycle, automobile, sewing machine, or farm wagon? Can 

 there ever be a truly automatic machine ? 3. Why is there less friction 

 in a machine with roller or ball bearings than in one with bearings of 

 the usual type? 4. How does a set of pulleys enable a man to accom- 

 plish work which he could not accomplish unaided? 5. If a rope is 

 arranged to run from a weight on the ground through a pulley attached 

 to an elevated beam and down to your hand, will less force be needed 

 to raise the weight than if no pulley were used ? 6. Why is one's finger 

 more likely to be crushed in a door if caught at the hinges than if 

 caught at the latch ? 7. When a long ladder is being raised, why must 

 the lower end be braced against some heavy object? 8. How and when 

 is water power used in getting the timber from the higher hilly or 

 mountainous regions to the more level plains or to sea level ? 



186. About work in general. A great deal of the work of 

 running water is of no immediate benefit to man. The great 

 waterfalls of the earth may continue for many centuries with- 

 out producing any noticeable change in the desirableness of 

 the surrounding region as a place of human residence. To 

 be sure, the gorge of Niagara may in time be extended so 

 far upstream that it will reach and partly drain Lake Erie, 

 but that event is far in the future. As a sublime spectacle 

 the Niagara Falls may be of very great value, but as a worker 



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