30 ANSWERS TO PRACTICAL QUESTIONS 



15. Can a swimmer tread on pieces of glass at the bot- 

 tom of the ivater with less danger than on land ? 



Yes. But he would still find it unadvi sable to try the ex- 

 periment. 



16. Will a vessel displace more water in a fresh river 

 than in the ocean ? 



In the fresh river, because the specific gravity, and hence 

 the buoyancy, of fresh water is less. 



17. Will iron sink in mercury ? 



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



18. The water in the reservoir in Neiv York is about SO 

 feet above the fountain in the City Hall Park. What is 

 the pressure on a single inch of the pipe at the latter point ? 



(1,000 oz. x 80) H- 144 = 34.7 Ibs. 



19. Why does cream rise on milk ? 



Because it is lighter than the milk. 



20. Ttiere is a story told of a Chinese boy who accident- 

 ally dropped Jiis ball into a deep hole, where he could not 

 reach it. He filled the hole with water, but the ball ivould 

 not quite float. He finally bethought himself of a lucky 

 expedient, which was successful. Can you guess it ? 



He put salt in the water. 



21. Which has the greater buoyant force, oil or water ? 



Water, because its density is greater. 



22. What is the weight of 4= cu. ft. of cork ? 



1,000 oz. = the weight of 1 cu. ft. of water. 

 .240 = the spec. grav. of cork. 



240 oz. = the weight of 1 cu. ft. of cork. 

 4 



960 oz. = the weight of 4 cu. ft, of cork, 

 = 60 Ibs. 



