1 84 GENERAL SCIENCE 



position of the fulcrum with respect to the force and 

 weight. 



(a) The lever of the first class is one with the fulcrum 

 between the force and the weight. Examples of this 

 class are: common steelyards, scissors, the balancing arm 

 of platform scales, most pump handles, and a crowbar 

 when it is shoved under an object, a fulcrum put under 

 and the force end shoved downward, thus lifting the 

 object upward. 



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LEVERS or THE SECOND CLASS 



(5) The lever of the second class is one with the weight 

 between the force and the fulcrum. Examples of this 

 class are: the nut-cracker with the fulcrum at the hinge, 

 the force at the handle (the weight is the pressure put on 

 the nut to crack it); the wheelbarrow with the fulcrum 

 at the axle of the wheel and the force at the handles; 

 the foot when we stand on the toes, which form the ful- 

 crum, the weight being on the ankle joint, and the force 

 applied at the heel. In the lever of the second class the 

 force arm is the entire lever-bar; the fulcrum is at one 

 end and the force at the other. The force arm is the 

 distance from the force to the fulcrum. The weight 

 arm is the distance from the weight to the fulcrum. A 

 bar 10 feet long will give a higher mechanical advantage 

 if it is used as a lever of the second class than if it is 

 used as a lever of the first class. 



(c) The lever of the third class is one with the force 

 between the weight and the fulcrum. Examples of this 

 class are: the pitchfork with the weight on the end, the 



