CHAPTER XVI 

 MECHANICAL ENERGY AND HEAT 



197. Questions for Discussion. 1. Can a boy kick a football harder 

 by kicking it from a standing position or by running a few steps be- 

 fore kicking it? 2. Would two persons walking toward one another 

 until they came in contact strike harder than when running toward 

 one another ? 3. Does a moving train possess energy after the engine 

 driver shuts off steam ? 4. What becomes of the energy of a moving 

 train when the brakes are set? 5. Why does a gasoline engine, when it 

 is burning a given amount of gasoline, heat up more readily when run- 

 ning idle than when pulling hard? 6. If a piece of metal is pounded, 

 or a piece 9f armor plate is struck by a cannon ball, the metal becomes 

 hot. Why? 7. Water becomes heated when it is used to cool a gaso- 

 line engine. Does this represent a waste of energy? 8. What are the 

 principal wastes of energy by a gasoline engine? 9. Why does a saw 

 become hot when in use ? 10. Does an auger heat more in soft wood 

 or in hard? 11. Coal has sometimes been called preserved sunshine. 

 In what sense is this true? 12. Wo'uld it be possible to use steam, 

 gas, or electric engines if work that has been done by the sun were 

 not available? 



198. Capacity for doing work. In the experiments with 

 the system of pulleys which were discussed in the preced- 

 ing chapter the force was applied at the end of the cord. 

 The same results might have been obtained in another way. 

 A weight of some sort might have been attached to the 

 end of the cord; if this were of the proper size it would, 

 when released, descend and cause the load carried by the 

 movable pulley to rise. It requires work to raise the load, 

 and it therefore follows that the weight upon the end of 

 the cord is able to do work. Also the pull upon the cord 

 might have been supplied by an electric motor or by a 

 steam engine. In either case the weight, the motor, or the 



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