IN NA TUB A L PHILOSOPHY. I 5 



MOTION. 



8O. i. Can a rifle-ball be fired through a handkerchief sus- 

 pended loosely from one corner? 



Yes. The wind of the ball will lift the handkerchief somewhat. 



2. A rifle-ball thrown against a board standing edgewise 

 will knock it down j the same bullet fired at the board will 

 pass through it "without disturbing its position. Why is this? 



The ball which is thrown has time to impart its motion to 

 the board ; the one fired has not. 



3. Why can a boy skate, safely over a piece of thin ice, when, 

 if he should pause, it would break under him directly ? 



In the former case there is time for the weight of his body to 

 be communicated to the ice ; in the latter, there is not. 



4. Why can a cannon-ball be fired through a door standing 

 ajar, without moving it on its hinges ? 



Because the cannon-ball is moving so quickly that its motion 

 is not imparted to the door. 



5. Why can we drive on the head of a hammer by simply 

 striking the end of the handle ? 



This can only be done by a quick, sharp blow which will 

 drive the wooden handle through the socket before the motion 

 has time to overcome the inertia of the iron head. A slow, 

 steady blow will be imparted to the head, and so fail of the 

 desired effect. 



6. Suppose you were on a train of cars moving at the rate 

 oj '30 miles per hour : with what force would you be thrown 

 forward if the train were stopped instantly? 



With the same velocity which the train had, 01 44 feet pet 

 second. Your momentum would be your weight avoirdupois 

 multiplied by this velocity. 



7. In what line does a stone fall from the mast-head of a 

 vessel in motion ? 



In a curved line, produced by the two forces gravity and 

 the forward motion of the vessel. 



