Leeson V.j 







which chiefly c.mses this force, and is at- 

 tached to the lower jaw, B, at P. The 

 fulcrum. F, is formed by the condylt or end 

 of the bone, which rests against the tem- 

 poral bone, T, while the weight or resistance 

 is at w. 



55. T. Give me some examples of 

 compound levers of the third class. 



P. A pair of shears, such as ar 

 for shearing sheep, and a pair of tongs, 



.:.les. In both en- 

 action is, the same ; and here is a diagram 

 F r 



of a pair of tongs which will illustrate this. 

 i' P. the parts where we 

 lay hold of the tongs, represents the power; 

 and the coJ, W, is the weight or resist- 

 ance. 



:.VL QUESTIONS ON LKSSON IV. 



1. Give an explanation of the decompo- 

 sition of the forces acting upon a levrr. !>j 

 means of the theory of the parallelogram 

 of forces, and explain how equilibrium is 

 maintained. 



\plain the meaning of the static 

 moment of the force of a lever. 



.'}. Define a lever of the second kind. 



4. Give spme examples of levers of the 

 second class. 



.'>. What do you mean by a one-arm-'d 

 lever? 



t). Explain how a one-armed lever acts. 



7. Define a lever of the third kind. 



8. Is there any advantage to l.e gained 

 in iiNing levers of the third class? 



9. Give some examples of third-class 

 levers. 



10. Are levers of the third class single 

 or compound ? 



LESSON V. 



IF we \vi>h to have a very long lever, or one possessing great mechanic il power, it is 

 10 arrange a series of levers, so that the power acting on the end of the first lever 

 hall raise the second, and that, depressing the end of the third, will raise a weight at 

 the further example, suppose tli.v loot) pounds by 



means of one pound, the distance of the j> .u, r from the fulcrum must he 1000 times 

 that of the weight, and as this would be very incoir. e levers for 



the purpose of obtaining the same result. The relative length of the a 

 lever it a* ten to dne ; and if we /'/'#. 17, we shall see that the levers are so 



arranged, as to bear upon one another. '1 liu.>, the power of one pound w,K balance the 







r -tr 



,\ 



weigh' md; and as the weight end of the first lev 



econd lever, it Mill exercine a force of ten pounds upon it. Tiic 

 K raised with a f 

 ige as the first, v 



with a force rqtul to loo pounds. This force of 100 pound*, being applied 

 : >S and raise 



tiie ui-j;ii: ;. 1 ith a force of 1000 pounds. 



