yo Common Science 



overcame part of your inertia, for he made you move 

 a little. 



Inertia is the tendency of a thing to keep on going 

 forever in the same direction if once it is started, or 

 to stand still forever unless something starts it. If mov- 

 ing things did not have inertia (if they did not tend to 

 keep right on moving in the same direction forever or 

 until something changed their motion), you could not 

 throw a ball ; the second you let go of it, it would stop 

 and fall to the ground. You could not shoot a bullet 

 any distance ; as soon as the gases of the gunpowder 

 had stopped pushing against it, it would stop dead and 

 fall. There would be no need of brakes on trains or 

 automobiles ; the instant the steam or gasoline was shut 

 off, the train or auto would come to a dead stop. But 

 you would not be jerked in the least by the stopping, 

 because as soon as the automobile or train stopped, your 

 body too would stop moving forward. Your auto- 

 mobile could even crash into a building without your 

 being jarred. For when the machine came to a sudden 

 stop, you would not be thrown forward at all, but would 

 sit calmly in the undamaged automobile. 



If you sat in a swing and some one ran under you, you 

 would keep going up till he let go, and then you would 

 be pulled down by gravity just as you now are. But 

 just as soon as the swing was straight up and down 

 you would stop ; there would be no inertia to make you 

 keep on swinging back and up. 



If the inertia of moving things stopped, the clocks 

 would no longer run, the pendulums would no longer 

 swing, nor the balance wheels turn; nothing could be 



