28 SCIENCE OF COMMON THINGS. 



Examples of action and reaction. Laws of falling bodies. 



Because the side of the house resists the ball with 

 the same force, and the ball, being elastic; rebounds. 



158 When the same ball is thrown against a pane of glass with the 

 same force, it goes through, breaking the glass : why does it not rebound as 

 beforef 



Because the glass has not sufficient power to resist 

 the full force of the ball : it destroys a part of the force 

 of the ball, but the remainder continuing to act, the 

 ball goes through, shattering the "glass. 



159 Why did not the man succeed who undertook to make a fair wind 

 for his pleasure boat, by erecting an immense bellows in the stern, and blow- 

 ing against the sails f 



Because the action of the stream of wind and the 

 reaction of the sails were exactly equal, and, conse- 

 quently, the boat remained at rest 



160 If he had blown in a contrary direction from the sails, instead of 

 against them, would the boat have moved ? 



It would, with the same force that the air issued from 

 the bellows-pipe. 



161 Why cannot a man raise himself over a fence by pulling upon the 

 straps of his boots f 



Because the action of the force exerted to raise him- 

 self, is exactly counteracted by the reaction of the force 

 which tends to keep him down. 



163 Does a man, in rowing, drive the water astern with the same fores 

 that he impels the boat forwards t 



He does : action and reaction being exactly equal. 



163 Why is it more dangerous to leap from a, high window than from 

 a low table ? 



Because the velocity of a falling ~body, and, conse- 

 quently, the force with which it will strike the ground," 

 ^ncrease8 with the distance through which it falls. 



164 How far ivitt a, body fall, through the influence of gravity, in one 

 te.cond of time ? 



Sixteen feet. 



165 How far will it fall in two seconds f 



Four times 16 feet, or 64 feet ; in three seconds it 

 will fall 144 feet ; in four, 256 ; in five seconds, 400 

 feet, and so on. 



