220 



THE HUMAN BODY AS A MACHINE 



3. MUSCLES AS PART OF A MACHINE 



Note. The instructor should here briefly explain the 

 principle of the lever, as well as the three classes or kinds. 



Designate them by the fac- 

 tor placed in the middle. 



Method a. Kaise a book 

 in the right hand. 



Observation. Locate the 

 power, weight, and fulcrum. 

 What represents each ? 

 Use Figure 53 in locating 

 P, W, and F. 



Conclusion. What class 

 of lever is represented 

 here ? (Make a sketch to 

 show your conclusion.) 



Method b. Stand on tip- 

 toe. 



Observations. 1. What 

 is the effect on the muscle 

 in the calf of the leg ? 



2. Locate weight, ful- 

 crum, and power. 

 Conclusion. What class of levers represented here ? Make 

 a sketch to show your conclusion. 



\ 



FIG. 53. Diagram showing action of 

 biceps muscle, a, contracted; b, ex- 

 tended ; h, humerus ; s, scapula. 



A B 4 C 



FIG. 54. Forms of levers. A, first class; B, second class; (7, third class; 

 W, weight; F, fulcrum or pivot; P,pull or power. 



