MOMENTUM. 



25 



through the water, the motion, at first slow, is con- 

 stantly accelerated tiU the increasing resistance of the 

 water to the moving mass becomes equal to the strength 

 of the engine and the momentum.* Were it not for 

 the momentum of moving bodies (inertia existing), 

 no speed ever could be given to any heavy body, as a 

 carriage, boat, or train of cars. 



The chief danger in fast riding, or fast travehng of 

 any kind, is from the momentum given to the trav- 

 eler. If a rail-way passenger should step from a car 

 when in full motion, he would strike the earth with 

 the same velocity as that of the train ; or if the train 

 at thirty miles an horn* should be instantly stopped, 

 the passengers would be pitched forward with a swift- 

 ness equal to thirty miles an hour. When a horse 

 suddenly stops, the momentum of the rider tends to 

 throw him over the horse's head. Wlien a wagon 

 strikes an obstruction, the driver falls forward. A 

 case in court was once decided against the plaintiff, 

 who claimed that the defendant had driven against his 

 wagon with such force as to throw the plaintiff to a 

 great distance ; but the fact was shown that by such 

 momentum he himself must have been driving furi- 

 ously, and not the defendant, and he lost his suit. 



An African traveler once succeeded in saving his 

 life by a ready knowledge of this principle. He was 

 closely pursued by a tiger, and when near a precipice, 

 watchmg his opportunity, he threw his coat and hat 



* In ordinary practice, this is not strictly correct, as friction will 

 make some difference. This influence will be more particularly 

 considered on a subsequent page. Its omission here does not at all 

 alter the principle under consideration. 



B 



