62 WELLS'S NATURAL PHILOSOPHY. 



4. If a body be projected do-irnward with a velocity of twenty-two feet in the first sec- 

 ond of time, liow far will it fjiU in eight Beconds ? 



The multiple in this case will be the distance fallen through in the first second. 



5. What space will a body pass through in the fourth second of its time of falling T 



6. A body falls to the ground in eight seconds ; how largo a space did it pass over dur- 

 ing the last second of its descent? 



7. A body falls from a height in eight seconds ; with what velocity did it strike the 

 ground ? 



8. A cannon-ball fired upward, continued to rise for nine seconds ; what was its velocity 

 during the first second, or with what force was it projected? 



9 Suppose a bullet fired upward from a gun returned to the earth in sixteen seconds; 

 how high did it ascend ? 



The time occupied in ascending and descending being equal, the body rose to such a 

 heii^ht that it required eight seconds to descend from it. The square of 8=64. This 

 multiplied by the space it would fall in the first second, IC feet = 924 feet. 



10. A bird was shot while flying in the air, and fell to the ground in three seconds. 

 How high up was the bird when it was shot ? 



11. What must be the length of a pendulum to vibrate once in seven seconds ? 



12. If the length of a pendulum to vibrate seconds at Washington is 39.101 inches, hovr 

 long must it be to vibrate half seconds? IIow long to vibrate quarter seconds? 



CHAPTER V. 



MOTION. 

 What is Mo- 124. Motion is the act of changing place. 



t'on ? If no motion existed, the universe would be dead. There 



would be no alternation of the seasons, and of day and night ; no flow of 

 water, or change of air ; no sound, light, heat, or animal existence. 



125. Motion is Absolute or Kelative. 



solute and Rei"- ABSOLUTE MoTiON is a changc of position in 



ative Motion ? • i i • 1 1 / /• , 



space, considered without relerence to any 

 other body. Relative Motion is motion considered in 

 relation to some other body, which is either in motion or 

 at rest. 



Thus the motions of the planets in space are examples of Absolute Motion, 

 but tlic motion of a man sitting upon the deck of a vessel, while sailing, 13 

 an example of Eelative Motion, since he is in motion as respects the land, 

 but at rest as regards the parts of the vessel. Rest, which is the opposite 

 cf motion, so far as we know, exists only relatively. We say a body on the 

 surface of the earth is at rest, when it maintains a constant position as re- 

 gards some other body ; but at the same time that it is thus at rest, it partakes 



