FALLING BODIES. 65 



increases its velocity every second by the quantity g. 

 When a body is thrown upward, gravity diminishes its 

 velocity every second by the same quantity. Hence the 

 time of its ascent will be found by dividing its initial 

 velocity by g. The initial velocity of a body that 

 can rise against the force of gravity for a given 

 number of seconds is the same as the final velocity 

 of a body that has been falling for tine same 

 number of seconds. 



(a.) The spaces traversed and the velocities attained during suc- 

 cessive seconds will be the same in the ascent, only reversed in 

 order. If a body be shot upward with a velocity of 821.6 feet, it 

 will rise for ten seconds, when it will fall for ten seconds. The 

 tenth second of its ascent will correspond to the first of its descent, 

 i. e., the space traversed during these two seconds will be the same ; 

 the eighth second of the ascent will correspond to the third of its 

 descent ; the end of the eighth second of its ascent will correspond 

 to the end of the second second of its descent. 



133. Projectiles. Every projectile is acted upon by 

 three forces : 



(1.) The impulsive force, whatever it may be. 

 (2.) The force of gravity. 

 (3.) The resistance of the air. 



134. Random or Range. The horizontal dis- 

 tance from the starting-point of a projectile to 

 where it strikes the ground is called its random 

 or range. In Fig. 30, the line GE represents the ran- 

 dom of a projectile starting from F, and striking the 

 ground at E. 



135. Path of a Projectile. The path of a pro- 

 jectile is a curve, the resultant of the three forces above 

 mentioned. Suppose a ball to be thrown horizontally. 

 Its impulsive force will give a uniform velocity, and may 



