36 



MECHANICS. 



er, 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 exhibited hy the following 

 table :* 



A stone or other body wiU 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 prec- 

 ipice, 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 peb- 

 ble to a cord, which will swing from the hand in reg- 

 ular vibrations of an exact second each if the cord be 

 39 1 inches long, or of half a second each if it be about 

 9§ inches long. 



The velocity increases simply as the time — that is, 

 the speed in falling is twice as gi-eat in two seconds 

 as in one ; three times as great in three seconds ; four 

 times as great in four seconds, and so forth. A stone 

 will. fall four times as far in two as in one second, while 



* The distance, accurately stated, is sixteen feet and one inch for 

 the first second, and hence the numbers in the table fall a very little 

 short of the distance actually fallen. 



