SOME EFFECTS OF NEWTON'S LAWS 57 



Experiment 51. Drop pieces of different substances (wood, 

 stone, iron, lead, and others) from the same height exactly 

 together, and note whether or not they strike together. 

 Repeat several times, for accuracy. 



Compare with these the fall of a leaf or sheet of 

 paper. Note and explain any differences. 



Falling bodies offer almost the only common 

 example of motion which is not opposed by 

 any considerable force ; for generally only the 

 air hinders their progress, and its force is not 

 great. Thus it is interesting to note this sort 

 of motion carefully. It has been found that 

 a body will fall about sixteen feet in one second. 

 But at the end of that second its momentum 

 alone is great enough to carry it about thirty- 

 two feet in a second. The result is that in 

 the second second the body will travel thirty- 

 two feet because of its momentum (or inertia) 

 and sixteen feet by force of gravity, making a 

 total of forty-eight feet. So as it goes on it 

 loses little or none of its momentum and con- 

 stantly gathers more, as gravity keeps acting upon it ; 

 so that the farther a body falls, the faster it goes. This 

 is why a long fall generally does more damage than a 

 short one. 



67. Pendulum. A pendulum is a device so sup- 

 ported that it is free to swing to and fro about a fixed 

 point. Fig. 44 shows a pendulum, a being its point of 

 support (on which it swings) and b the weight or bob. 

 Lift b to the position c and let it go ; gravity acts upon 

 it, pulling the bob downward toward e. At the position 



