TOOLS BASED ON THE LEVER 59 



the end having two books? Compare the lengths of these two 

 arms of the lever. 



Finally put three books at one end and one at the other, and 

 compare the lengths of the two arms of the lever. 



Is it true in the first case that the weight arm multiplied by 

 its load is equal to the power arm multiplied by its load; that 

 is, that the weight arm multiplied by its number of books is 

 equal to the power arm multiplied by its number of books? 



Is it true in the second case? In the third? 



c. Make a second-class lever as in Fig. 23, B. Put the book 

 near the fulcrum, and lift upward at the end having the arrow. 

 Move the book toward the hand, and note how much effort 

 you need to put forth to lift the power arm. Where is the book 

 when the lifting is most easy? When it is most hard? What 

 is the greatest force you must exert in lifting a weight with a 

 second-class lever? 



d. Make a third-class lever as in Fig. 23, C, using your left 

 hand as a loose fulcrum to keep the fulcrum end from slipping 

 out of place. Put the book on the other end of the lever, and 

 with your right hand lift upward at the left of the book. Try 

 lifting upward at several places, each one a little nearer the 

 fulcrum. What are the results? At which part of the lever is 

 the lifting most easy? What is the smallest weight you must 

 lift in raising a book by means of a third-class lever? 



e. Use a book cover as a lever, placing a weight upon it. 

 Find where the weight is when the greatest effort is needed to 

 lift it. Where is the weight when the least effort is needed? 

 To what class of levers does the book cover belong? 



EXERCISE 57 

 TOOLS BASED ON THE LEVER 



Apparatus. Jackknife, scissors or shears, can openers, hammer, 

 board, nail, nail extractor. 



