PROPERTIES OF MATTER 



45 



When we tried suddenly to lift the suspended ball, the 

 light string snapped because it could not withstand the 

 sudden additional strain of overcoming the ball's inertia. 

 When we exerted a very gradual pull on the upper string, 



AIRPLANES 



we overcame the inertia of the ball slowly and without sudden 

 strain to the string. 



When the lower string was suddenly pulled, it broke 

 because the ball, through its inertia, withstood the sudden 

 effort to change its position. But when the string attached 

 to the bottom of the ball was pulled gradually, the upper 

 string broke. In this case, the inertia of the ball was over- 

 come without sudden strain to the lower string, and so this 

 string had to withstand practically nothing but the pull of 

 the hand. The upper string, on the other hand, had to 



