THE ELEMENTS OF MACHINERY. 93 



it moves in a vertical direction, is greater than the pro- 

 duct arising from the weight multiplied by the space 

 through which it moves in a vertical direction. 



«rj) f J g t Practical men express the principle of equilibrium in ma- 



ty the ex- chinery by saying " that what is gained in power is lost in 

 w * gained*''»t^ time." Thus, if a small power acts against a great resistance, 

 the expense of the motion of the latter will be just as much slower than that 

 '™® of the power, as the resistance, or weight, is greater than tha 



power ; or if one pound be required to overcome the resistance of two pounds, 

 the one pound must move over two feet in the same time that the resistance,, 

 two pounds, requires to move over one. 



SECTION I. 



THE ELEMENTS OP MACHINERY. 



195. All machines, no matter how complex 



How many rim- ... , . . , 



pie machinei and mtricatc their construction, may be re- 

 duced to one or more of six simple machines, 

 or elements, which we call the " Mechanical Powers." 

 , ^ 196. They are the Lever, the Wheel and 



Enumerate the '' ' 



Bii elementary AXLE, the PULLEY, the INCLINED PlANE, the 



Wedge, and the Screw. 



These simple Machines may be further reduced to three — the lever, the 

 pulley, and the incUned plane ; since the wheel and axle, the screw and the 

 wedge, may be regarded as modifications of them. 



The name " mechanical powers ' which has been applied to the six ele- 

 mentary machines, is unfortunate, since it serves to convey an idea that they 

 are really powers, when in fact they possess no power in themselves, and aro 

 only instruments for the application of power. 



What it a 197. A Lever consists of a solid bar, straight 



Lever » ^^ bent, tuming upon a pivot, prop, or axis. 



What are the 1^8. The Arms of the IcvcF are those parts. 



Anns of a Le- ^f ^j^g ^jg^j. extending on each side of the 

 axis. 



What Is the 199. The Fulcrum, or prop, is the name 



Fulcrum applied to the axis, or point of support. 



„ 200. Levers are divided into three kinds, or 



How many ... 



kinds ofieveri classcs, accordin^T to the position which the 



*re there t n ^ ^ • ^ • i 



luicrum has in relation to the power and the 

 weight. 



