86 MECHANICS. 



the wheels and blocks and the stiffness of the cordage, 

 which are often so great that two tliirds of the power 

 is lost. 



SECTION VI. 

 THE INCLINED PLANE. 



The inclined plane or slope possesses a power which 

 is estimated by the proportion which its length bears 

 to the height. If, for example, the plane be twice as 

 long as the perpendicular height, 

 then in rolling the body, «, up 

 the inclined plane {Fig. 69), it 

 will move through twice the dis- 

 tance required to lift it directly 

 from b to c. Therefore only one half the strength else 

 required need be exerted for this purpose. The same 

 reasoning will apply to any other proportion between 

 the height and length ; that is, the more gradual or 

 less steep the slope becomes, the greater will be the 

 advantage gained. A familiar example occurs in lift- 

 ing a loaded barrel into a wagon : the longer the plank 

 used in rolling it, the less is the exertion needed. 



A body, in rolling freely down an inclined plane, ac- 

 quires the same velocity that it would attain if dropped 

 perpendicularly from a height equal to the perpendic- 

 ular height of the plane. Thus, if an inclined plane 

 on a plank road be 100 yards long and 16 feet high, a 

 freely running wagon, left to descend of its own accord, 

 will move 32 feet per second by the time it reaches 

 the bottom, that being the velocity of a stone falling 

 16 feet. Or, a rail-car on an inclined plane 145 feet 



