CHAPTER VII 



THE FOOT AND THE FOREARM AS LEVERS 



No matter what part of the human body we examine, we 

 shall find that its mechanical work is performed by means 

 of bony levers. Having seen how the head is moved as 

 a lever of the first order, we are now to choose a part 

 which will show us the plan on which levers of the 

 second order work, and there are many reasons why we 

 should select the foot. It is a part which we are all 

 familiar with ; every day we can see it at rest and in 

 action. The foot, as we have already noted, serves as a 

 lever in walking. It is a bent or arched lever (fig. 14) ; 

 when we stand on one foot, the whole weight of our 

 body rests on the summit of the arch. We are thus 

 going to deal with a lever of a complex kind. 



In using a chisel to prise open the lid of a box, we 

 may use it either as a lever of the first or of the second 

 order. We have already seen (fig. 9) that in using it 

 as a lever of the first order we pushed the handle down- 

 wards while the bevelled end was raised forcing open the 

 lid. The edge of the box served as a rest or fulcrum for 

 the chisel. If, however, after inserting the bevelled edge 

 under the lid, we raise the handle instead of depressing 

 it, we change the chisel into a lever of the second order. 

 The lid is not now forced up on the bevelled edge, but 

 is raised on the side of the chisel, some distance from the 

 bevelled edge, which thus comes to represent the fulcrum. 

 By using a chisel in this way we reverse the positions of 

 the weight and fulcrum and turn it into a lever of the 

 second order. Suppose we push the side of the chisel 



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