i86 GENERAL SCIENCE 



ical advantage if the weight is 2 feet from the fulcrum? How large 

 could the weight be if a force of 100 pounds would just lift it? 



4. If a lever of the first class is 10 feet long, and the fulcrum is 

 2 feet from the end, what is the mechanical advantage? How 

 much force will be required to lift a weight of 600 pounds? 



6. A lever of the third class is 10 feet long, with the force 2 feet 

 from the fulcrum. What force is required to lift a weight of 10 

 pounds? What is its mechanical advantage? 



124. The Inclined Plane. The inclined plane is a 

 simple device, often composed of one or more planks 

 elevated at one end, so that objects may be rolled up 

 or down. In order to understand the principle of the 

 inclined plane, let us recall some of our experiences. We 

 know that we become tired more quickly walking up a 

 grade than while walking on the level, and the steeper 

 the grade the more force it takes to ascend it. It is 

 harder to ride a bicycle up a steep grade than to ride up 

 a very gradual grade. The hill that is hard to climb in 

 winter is the one down which we can coast the fastest. 

 We can see from our own experiences that the slope of 

 the plane is what determines the force required to roll 



^- an object up it, and 

 F the length of the 

 plane determines the 

 amount of work done 



while rolling an ob- 

 ject up it. 



To test our obser- 

 vations let us try an 

 INCLINED PLANE 



experiment with a 



plane, a rolling weight, and a spring balance. In the illus- 

 tration, the length of the plane is AB, the height is BC, the 

 weight moving up is W, and the force moving it is F, 

 measured by the spring balance. If the height BC is 



