Machines 249 



sufficient to do it, he may accomplish his purpose with comparative 

 ease by rolling the barrel up a long, inclined plank and by exerting 

 his force in a direction parallel to the incline. 



The boy accomplishes the same work whether he lifts the 

 barrel directly into the wagon, or rolls it up the incline. He 

 moves it farther by rolling it up the incline, but with less 

 effort. 



It is evident that the more gradual the incline, the less the 

 effort necessary to accomplish the work. The mechanical advan- 

 tage gained is equal to the length of the inclined plane divided 

 by its height. If the length is four times the height, then a 

 force of one pound will balance a weight of four pounds on the 

 inclined plane. 



THE INCLINED PLANE 



A small weight holds the heavy roller in its place. Why? 



The stairways in our houses are inclined planes, the steps 

 merely enabling us to obtain a firm foothold. Highways and 

 railroads are constructed so that the grades are as gradual as 

 possible. Much more effort is needed to drive an auto- 

 mobile or an engine up a steep hill than up one of the same 

 height where the rise is gradual. Naturally the distance covered 

 is greater. Power is gained at the expense of time in the use of 

 the inclined plane. 



