CHAPTER XI 

 MECHANICAL USES OF WATER AND AIR 



146. Questions for Discussion. 1. What is the principle of drinking 

 through a straw ? 2. A coarse towel was left hanging over the edge 

 of a partially filled bathtub, one end of the towel extending into the 

 water, the other end hanging outside. When it was discovered there 

 was a small pool of water on the floor. How did this take place? 

 3. How does a pump lift a liquid ? 4. What is the difference between 

 a force pump and a suction pump? 5. How is water picked up by a 

 tornado on the sea ? 6. Why does liquid flow from small-necked bottles 

 with a gurgling noise? 7. Why is it difficult to pour oil into a can 

 steadily if the funnel used fits the opening closely? Why does lifting 

 the funnel help? 8. How is water forced to the tops of tall buildings? 



9. Why does an iron ship float? How can a submersible boat remain 

 on the surface part of the time and under water part of the time? 



10. Why can a submarine not safely descend to the bottom in the 

 deeper parts of the ocean? 11. Why are dams commonly thicker at 

 the bottom than at the top? 12. If an object floats in water almost sub- 

 merged, how would it behave in oil? in kerosene? in a gas? 13. What 

 is the principle by means of which a balloon may rise in the air? Is a 

 dirigible balloon heavier than air? is an aeroplane? 14. How rapidly 

 can an aeroplane ascend? What is the record height reached by an 

 aeroplane ? the record long-distance flight ? 



147. Water transferred by the siphon. The siphon may be 

 used to transfer water or other liquid from one vessel to 

 another over an elevation. This can be done only in case 

 the outlet of the siphon is at a lower level than the surface 

 of the liquid which is being transferred. For instance, in 

 the illustration (fig. 65) the tube, which serves as a siphon, 

 is represented as transferring water from the beaker at A 

 to the one at D, which is at a lower level. In starting 

 a siphon to work it is necessary to fill the tube with the 



