26 ANSWERS TO PRACTICAL QUESTIONS 



The pressure is proportional to the height and not the size of the column, 

 hence the pressure ia 



20 x 250 x 1000 oz. = 5,000,000 oz. = 312,500 Ibs. 



10. Why can stones in water be moved so imtch mort easily 

 than on land? 



Because the water buoys up about one-half of their weight. 



11. Why is it so difficult to wade in the water where there 

 is any current? 



Because the buoyant force of the water makes us so light 

 that we are easily carried away from our footing. 



12. Why is a mill-dam or a canal embankment small at the. 

 top and large at the bottom ? 



Because the pressure of the water increases with the depth. 



13. In digging canals and building railroads, oiight not the 

 engineer to take into consideration the curvature of the earth ? 



Certainly. If he should build on a true level he would find 

 his embankment pointing up to the stars. 



14. Is the water at the bottom of the ocean denser than that 

 at the surface f 



The immense pressure must condense it very much at great 

 depths. There is a certain point beyond which divers cannot 

 penetrate. 



15. Why does the bubble of air in a spirit-level move as the 

 instrument is turned? 



Because the air is lighter than the alcohol and rises con- 

 stantly to the highest point. For this reason, also, the tube 

 is curved upward at the centre. 



1 6. Why can a swimmer tread on glass and other sharp 

 substances at the bottom of the water with little harm ? 



See problem 11. 



1 7. Will a vessel draw more water in salt or in fresh water f 

 In fresh, because its specific gravity is less. 



1 8. Will iron sink in mercury ? 



No. It will float, like a cork on water. 



19. The water in the reservoir in New York is about 80 feel 



