FOOT AND FOREARM AS LEVERS 



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the lever somewhere between the muscular attachment 

 and the fulcrum. In levers of the third order the load is 

 placed at the end of the lever, and the muscle is attached 

 somewhere between the load and the fulcrum (fig. 17A). 

 In the example we are considering the brachial muscle is 

 attached about half an inch beyond the fulcrum at the 

 elbow, while the total length of the lever, measured from 

 the elbow to the palm, is 12 inches. Now, it is very- 

 evident that the muscle or power being attached so close 

 to the elbow, works under a great disadvantage as regards 

 strength. It could lift a 24-lb. weight placed on the 



FlG 17A. — A chisel used as a lever of the third order. W, weight ; 

 P, power ; F, fulcrum. 



forearm directly over its attachment as easily as a single 

 pound weight placed on the palm. But, then, there is 

 this advantage : the i-lb. weight placed in the hand moves 

 with twenty-four times the speed of the 24-lb. weight 

 situated near the elbow. What is lost in strength is 

 gained in speed. Whenever Nature wishes to move a 

 light load quickly she employs levers of the third order. 



We have often to move our forearm very quickly, 

 sometimes to save our lives. The difference of one- 

 hundredth of a second may mean life or death to us on 

 the face of a cliff when we clutch at a branch or jutting 

 rock to save a fall. The quickness of a blow we give or 

 fend depends on the length of our reach. A long fore- 

 arm and hand are ill adapted for lifting heavy burdens ; 

 strength is sacrificed if they are too long. Hence we 



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