22 



MOTION LEVERS. 



hand and what is in it ; the fulcrum is the elbow joint ; and 

 the power is the point where the tendon of the biceps is 

 attached to the radius. This kind of a lever is what the 

 books call a lever of the third class. The triceps, on the back 

 of the arm, pulls on the projection of the ulna back of the 

 elbow. The elbow is here, also, the fulcrum, and the hand 

 (or the object to be pushed by the hand) is the weight. This 

 kind of lever, where the fulcrum is between the power and 

 the weight, is called a lever of the first class. In raising the 

 weight of the body, by standing on tiptoe, we use a lever of 

 the second class. Here the ball of the foot is the fulcrum. 

 The weight is the weight of the whole body, resting on the 

 ankle joint, while the power is the calf muscle. We may find 

 many examples of levers in the body if we look for them. 



(1.) TAPPING ON FLOOR (2.) RISING ON TOE (3.) LIFTING WEIGHT 



Fig. 6. Three hinds of Levers as shown by the Foot. 

 P, Power. W, Weight. F, Fulcrum. 



The different classes of levers may be further illustrated 

 by different motions of the foot. In tapping the toes on the 

 floor while the heel is lifted, or in pressing down the ball of 

 the foot while running the treadle of a sewing-machine, we 

 have an example of a first-class lever. In raising the weight 



