IN POPULAR PHYSICS. 3 



10. Suppose a steamer in rapid motion and on its deck 

 a tnan Jumping. Can he jump farther by leaping the 

 way the boat is moving or in the opposite direction? 



It will make no difference as long as he jumps on the deck. 

 Should he jump off the boat, then the effect would be different. 



11. Could a party play ball on the deck, of an ocean 

 steam- ship when moving along at the rate of 2O miles 

 per hour, without making allowance for the motion of 

 the ship ? 



They could. The ball would have the motion of the ship, 

 and would move with it in whatever direction they might 

 throw it. 



37 12. Since "action is equal to reaction," why is it not 

 r,o dangerous to receive the "kick" of a gun as the force 

 of the bullet ? 



The kinetic energy varies as the square of the velocity ; and 

 the velocity with which the gun moves backward is as much 

 less than that with which the bullet moves forward, as the gun 

 is heavier than the bullet. For this reason a heavy gun will 

 kick much less than a light one. 



13. If you were to jump from a carriage in rapid 

 motion, would you leap directly totvard the sx>ot on which 

 you wished to alight? 



No ; because as one jumps from the carriage he has its for- 

 ward motion, and will go just as far ahead, while leaping, as 

 he would if he had remained in the carriage. He should, there- 

 fore, aim a little back of the desired alighting-place. 



14. If you wished to shoot a bird in swift flight, would 

 you aim directly at it? 



No. The bird will fly forward while the bullet is going to 

 it. One should, therefore, aim a little in advance. 



15. At ^vl^at parts of the earth is the centrifugal force 

 the least? 



The poles. The distance from axis to surface is there re- 

 duced to zero. 



