General Thought Questions 311 



20. Name common tools or instruments that illustrate the principle of 

 (a) the wheel and axle, (b) the wedge, (c) the pulley. 



21. Why is it easier to roll a barrel up a plank into a wagon than to lift 

 it up? 



22. How does an overflowing stream help the flooded lowlands ? How does 

 it injure them? 



23. What elementary machines can you locate in an automobile? 



24. Compare steamships and submarines. 



25. How does a steam engine differ from a steam turbine? 



26. Why isn't a cooling device as necessary on a steam engine as on a 

 gas engine? 



27. State advantages of motor transportation lines over steam transpor- 

 tation lines for small lots of freight. 



28. Compare a dirigible and a steamship. 



29. What might happen if most of the freight load of a steamer were 

 placed on one side? Why? 



30. Why are houses with heavy brick or stone walls likely to be cooler 

 in the summer and warmer in winter than ordinary wooden houses ? 



31. What supplies the energy that runs a clock? How is it applied? 



32. Name four ways in which land transportation affects our lives. 



33. Is it true or false that grass and shrubs will endure bitter cold better 

 if there is snow? W r hy? 



34. What would you add to a clay soil that bakes readily in the sun to 

 make it more usable for garden purposes? 



35. Why is it harder to stop a railway train than an automobile, if both 

 are 'going at high speed? 



36. Is it true or false that automobiles are seldom struck by lightning? 

 Why? 



37. Does a locomotive do more work in a fixed time in drawing a train 

 at 30 miles an hour than in drawing it at 40 miles an hour? Explain. 



38. If one cylinder of a four cylinder automobile motor fails to fire, how 

 does it affect the power of the motor? 



39. Why are copper wires for carrying electric current frequently wrapped 

 with cotton or silk? 



40. Why are the slides placed upside down in a projecting lantern? 



41. Why does not an electric heater "exhaust the air" as a stove does? 



42. Why are bricks baked? 



43. Why is new-laid concrete kept sprinkled with water on a very hot day? 



44. Name two processes that must occur in the atmosphere before rain 

 can fall. Give one cause of each process named. 



45. Is it true or false that hard water requires more soap to make a lather 

 than soft water? Why? 



