530 FARM AND SCHOOL PROBLEMS. * , 



6. The source of heat which is able to raise the temperature of a 

 pound of water 1 in one second, will raise how many foot-pounds in the 

 same time? 



7. If the same number of heat units (778.3 ft.-lbs.) that will 

 raise water 1 will raise a pound of sand from 32 to 37.23 what will 

 be the difference in the amount of the sun's energy expended in heating 

 1 pound of water and 1 pound of sand from 32 F. to 33 F.? 



(When heat is applied to ice at 32, it will expend all its energy in 

 changing ice to water and will not raise the temperature of the ice until 

 it is melted.) 



The temperature of ice cannot be raised. 



8. If the amount of heat required to melt 1 Ib. of ice is 142 units, 

 what will be the work done expressed in ft.-pounds? 



Solution : 142 x 778.3 = 110,518.6 foot-lbs. 



9. What would be the time required for 1 horse-power to melt 

 1 Ib. of ice? 



100,518.6 



=3.35 minutes. 



33,000 



10. When ice and salt are mixed, the changing from the solid to 

 the liquid form takes the heat from the cream so rapidly that the cream 

 in the ice cream freezer is quickly frozen. 



One weight of salt and two weights of snow or pounded ice will 

 assume a temperature of 18 C., or Fahr. 



PROBLEM. 



1. If 1 pound of water at C. be mixed with 1 pound of water at 

 80 C, what will be the temperature of this 2 Ib. mixture? 



FRICTION. 



When energy is transmitted to a machine there is loss of 

 power through friction ; but friction enables the belt to run a 

 wheel and the drivers of the locomotive to haul a load. 



Friction may be reduced by using wheels, oil, hard, smooth 

 and level surfaces. 



Fortunately friction retards the flow of streams. 



MECHANICAL METHODS OF REDUCING FRICTION. 



1. Rolling bearings as in grindstone. 



2. Ball bearings as in bicycle. 



