448 GENERAL SCIENCE 



If an automobile goes around a curve too quickly, it is tipped 

 because of the tendency of that automobile to continue in a straight 

 line. 



Children playing in the street often forget that it is dangerous 

 to use the public thoroughfare as a playground, since automobiles 

 and cars moving up and down the street can not be stopped instantly 

 by the drivers. 



Gravity. When one drops something from his hand he knows 

 that the object will fall toward the earth. People who go up in 

 aeroplanes know that when they get ready to come back to earth 

 a certain force will pull them downward toward it. Those who jump 

 from balloons know that this force is so great that parachutes are 

 required to counteract the force pulling toward the earth. This 

 force which pulls things toward the earth also holds all objects on 

 the face of the earth. The waters of the sea, the houses, the rocks 

 and the trees are all held on the surface of the earth by a force called 

 gravity. 



The Force of Gravity Varies with the Size of the Body. The 

 larger the body or planet the greater is the force of gravity of the 

 body for objects on its surface. The moon is about $ as large as 

 the earth. The pull of gravity on the moon is so much less than that 

 of our earth that a body weighs only f of what it would weigh on 

 the surface of the earth, and a jumper who jumps 5 feet on the earth 

 would be able, expending the same energy, to jump 30 feet on the 

 moon. 



Up and Down. Very few of us ever stop to think what " down " 

 really means. Objects are said to fall down from any height. We 

 seldom think that if two objects on opposite sides of the world should 

 fall from the same height at the same time, those objects would be 

 moving toward each other or, in other words, toward the center of 

 the earth. Down, then, is the direction toward the center of the 

 earth, and the end of " down " is at the center of the earth. 



Up is away from the center of the earth, and the beginning of 

 " up " is at that point, while the end of " up " is at a place so high 

 above the earth that the earth ceases to pull the object toward it. 

 For example, if an object could move directly up from the earth 

 toward the moon it would be going up until it reached the place 



