FALLING BODIES. 63 



which may be fastened in a horizontal position for the 

 support of K at the top of the graduated rod. This plate 

 may also be dropped to a vertical position, thus allowing K, 

 when loaded, to fall. A clock, with a pendulum beating 

 seconds, serves for the measurement of time, and the drop- 

 ping of the plate at the top of the pillar. A weight or 

 rider, m, is to be placed upon K, and give it a downward 

 motion. Levelling screws are provided by means of which 

 the graduated rod may be made vertical, and K be made 

 to pass through the middle of B. 



(a.) Suppose that K and K' weigh 315 grams each, and that the 

 rider m weighs 10 grams. When m is placed upon K and the plate 

 dropped by the action of the clock, the gravity of m causes the 

 weights to move. We now have the motion of 640 grams produced 

 by the gravity of only 10 grams. When this force (gravity) moves 

 only 10 grams it will give it a certain velocity. When the same 

 force moves 640 grams it has to do 64 times as much work, and can 

 do it with only ^ the velocity. In this way we are able to give to 

 K and m any velocity of fall that we desire. 



123. Experiments. Arrange the apparatus by sup- 

 porting K and m upon the shelf n. As the hand of the 

 clock passes a certain point on the dial, 12 for example, 

 the shelf n is dropped and the weights begin to move. By 

 a few trials, B may be so placed that at the end of one 

 second it will lift m from K, and thus show how far the 

 weights fall in one second. Other experiments will show 

 how many such spaces they will fall in the next second or 

 in two seconds ; in the third second or in three seconds ; 

 in the fourth second or in four seconds, etc. 



Suppose that B lifts off m at the end of the first second. 

 The moving force being no longer at work, inertia will 

 keep K moving with the same velocity that it had at the 

 end of the first second. By placing A so that K will reach 

 it at the end of the second second, the distance AB will 



