208 ANSWERS TO PRACTICAL QUESTIONS 



The adhesion between the glue and the wood is 

 stronger than the cohesion between the particles of 

 glue ; hence the thinner the layer of glue the fewer the 

 particles acted upon only by the latter or weaker force. 



GRAVITATION. 



62. 1-41. (See the Answers to these Queries on pp. 

 9 to 14 of this Key.) 



42. How long would it take for a pendulum one mile in 

 length to make a vibration ? 



(See Key, p. 13, Problem 37.) 



According to the second law of pendulums (Physics, 

 P- 59), 



i sec. : x : : A/39 : ^5280 x 12 in. 

 x 40 -f sec. 



43. How long would it take for a pendulum reaching 

 from the earth to the moon to make a vibration ? 



i sec. : x : : A/39-i in. : \/24o,ooo x 5280 x 12 in. 

 x = 5 hrs. 28 -+- minutes. 



44. Required the length of a pendulum that would 

 vibrate centuries. 



(i sec.) 2 : (100 x 365.25 x 24 x 60 x 60)^ : : 39.1 in. : x. 

 x = 6,145,674,053,727,272 + miles. 



SOLOMON SIAS. 



45. What would be the time of vibration of a pendulum 

 64 metres long ? 



(i sec.) 2 : x* : : i metre (nearly) : 64 metres. 

 x = 8 seconds (nearly). 



