INERTIA. EXPERIMEXTS AND EXAMPLES. 



13 



M 



card, throwing it to a distance, but leaving the ball upon 

 the hollow end of the stand. The same experiment may 

 be easily performed by placing a very small apple or other 

 solid on a card, the whole resting on a common sand-box, 

 or even the hollow of the hand. A sud- ^iz- 3. 



den snap with the finger will throw the 

 card away, while the apple will drop into 

 the cavity. The following experiment is 

 still more striking: Procure a thread 

 just strong enough to bear three pounds, 

 and hang upon it a weight of two pounds 

 and a half Another half pound would 

 break it. Now tie another thread, strong 

 enougli to bear one pound, to the lower 

 hook of the weight. If the lower thread 

 be pulled gradually, the nj^per thread 

 will of course break ; but if it be pulled 

 with a jerJc, the lower thread will break. 

 If the jerk be very sudden, the lower string will break, 

 even it be considerably stronger than the upper, the in- 

 ertia of the weight requiring a great force to overcome it 

 suddenly. The threads used in this experiment may be 

 easily had of any desired strength by taking the finest 

 sewing cotton, and doubling to any desired extent. 



This experiment shows the reason why a horse, when 

 he suddenly starts with a loaded wagon, is in danger of 

 breaking the harness ; and why a heavier weight may l>e 

 lifted with a windlass or pulley having a weak rope, if the 

 strain is gradual and not sudden. For the same reason, 

 glass vessels full of water are sometimes broken when 

 hastily lifted by the handle. When a bullet is fired through 

 a pane of glass, the inertia retains the surrounding glass 

 in its place during the moment the ball is passing, and a 

 round hole only is made; while a body moving more 

 slowly, and pressing the glass for a longer space of time, 

 fractures tlie whole pane. 



