2O AM8WERS TO PRACTICAL QUESTIONS 



There is a story told of a man who erected a huge pair of 

 bellows in the stern of his pleasure-boat, that he might always 

 have a fair wind. On trial the plan failed. In which di- 

 rection should he have turned the bellows f 



In the manner adopted at first, of turning the nozzle toward 

 ihe sails, the action of the wind against the sails and the re- 

 action of the bellows against the boat just balanced each other. 

 If the man had turned the nozzle backward he could have 

 saved the reaction of the bellows to move the boat. This 

 would, however, have been a most costly and bungling way 

 of navigation. 



If we whirl a pail of water swiftly around with our hand, 

 why will the water all tend to leave the centre of the pail ? 

 Why will the foam all collect in the hollow at the centre ? 



THE MECHANICAL POWERS. 



90. i. Describe the rudder of a boat as a lever. 



The water is the F, the boat the W, and the hand the P. 

 As the W is between the F and the P, it is a lever of the 

 second class. 



2. Show the change that occurs from the second to the third 

 class of levers, when you take hold of a ladder at one end and 

 raise it against a building. 



At first the ground is the F at one end, the hand the P at 

 the other, and the ladder the W hanging between ; hence this 

 is a lever of the second class. After a little, the F remaining 

 the same, the P is applied at one end, near the F, and the 

 ladder is the W hanging at the other ; hence this is now a 

 lever of the third class. 



3. Why is a pinch from the tongs near the hinge more 

 severe than one near the end f 



Because in the former case the tongs are a lever of the first 

 class in the latter, of the third. In the first class there is a 

 gain of power, in the third a loss. 



4. Two persons are carrying a weight 0/250 Ibs., hanging 



