GRAVITATION. VELOCITY OF FALLING BODIES. 



23 



tiou is called gravitation. The force with which a body- 

 is thus drawn is the iceight of that body. 



When a stone is dropped from the hand, its velocity is 

 at first slow, but continues to increase till it strikes the 

 earth ; hence, the further it falls the harder it will strike. 

 This accelerated motion is precisely similar to that of a 

 steam-boat when it first leaves the wharf; the force of 

 gravity may be compared to the driving power of the 

 engine, and the quickened velocity of the falling stone 

 to the increased headway of the boat. 



All bodies, whether large or small, fall equally fast, un- 

 less they are so light as to be borne up in part by the 

 resistance of the air. In the first second of time tl)ey fall 

 16 feet; in the second, 3 times 16, or 48 feet ; in the third 

 second, 5 times 16, or 80 feet, and so on. Or, if the whole 

 distance fallen be taken together, they fall 16 feet in one 

 second, 4 times 16 in two seconds, 9 times 16 in three 

 seconds, and so forth. In other words, the whole distance 

 is equal to the square of the time. This is plainly ex- 

 hibited in the foUowins: table : 



A stone or other body will fall 1 foot in a fourth of a 

 second, 3 feet the next fourth, 5 feet the third fourth, and 

 7 feet the last fourth ; which is the same as 4 feet in half 

 a second, 9 feet in three-fourths of a second, and 16 feet 

 for the whole second. 



The depth of an empty well, or the height of a preci- 

 pice, may be nearly ascertained by observing the time 

 required for the fall of a stone to the bottom. The time 

 may be measured by a stop-watch, or, in its absence, a 

 pendulum may be made by fastening a pebble to a cord, 

 which will swing from the hand in regular vibrations of 



