60 ELEMENTS OF SCIENCE 



The reader will at once understand that it is only 

 the resistance of the air which prolongs the feather's 

 descent. Accordingly, if they are made to fall in the 

 nearest approach to a vacuum which an air-pump can 

 produce, they will fall simultaneously. 



If a bullet be taken in the right hand and be allowed 

 to fall thence into the left hand through a height of a 

 few inches, it will give a slight blow. If it be allowed 

 to fall a yard, it will be felt more smartly, while if it 

 were to descend on the hand from a second-floor window 

 the blow would be severe. 



Therefore the longer a fall lasts the greater the 

 distance through which a body falk the greater is 

 its energy and the greater the rapidity of its motion. 

 The motion of a falling body is a uniformly accelerated 

 motion, because, the attraction between the earth 

 and the body never ceasing to act, the body gains a 

 fresh momentum every instant. Therefore it falls 

 to the ground with a velocity which is the aggre- 

 gate of all the indefinitely small but equal increments 

 of velocity thus communicated to it. 



Now it has been discovered that a falling body 

 acquires, at the end of the first second of its fall, a 

 velocity of about 32.2 feet a second i.e., a velocity 

 which would, alone, carry it through, say, 32 feet 

 during the second second. During this second, how- 

 ever, it will have fallen through only 16 feet. During 

 the second second it will fall through the 32 feet (from 

 the velocity with which it starts) and through 16 

 additional feet on account of the constant action of 

 the force of gravity. Similarly, it will fall 64 feet 

 during the third second plus 16 feet, and so on, as 

 shown by the following table wherein the time of 

 each second is represented by a similar length, vejo* 



