68 



LABORATORY EXERCISES 



A 



A 



V 



FIG. 23. 



a. For this exercise you need a strip of dry wood about 

 5 cm. (2 in.) wide and 45 cm. (18 in.) long. Make a triangular 

 block for a fulcrum (a spool laid on its side will do), and lay 

 .j ^ A the strip of wood 



(the lever) over the 

 fulcrum, as in Fig. 

 23, A. Put a book 

 near one end of the 

 lever, and push 

 downward at the op- 

 posite end. Change 

 the fulcrum so that 

 its positions vary 

 from almost under 

 the book to almost 

 under your hand. 

 When is it easiest to lift the book? When is it hardest? 

 Such a lever is of the first class. Where is the fulcrum placed 

 as regards the weight (the book) and the place where the power 

 (your hand) is applied? 



b. Vary the experiment by hanging the book in a sling of 

 stout twine (Fig. 24) and putting the loop of the string over the 

 lever, near one end. Use the back of a chair as the fulcrum. 

 Hang another book of the same weight at the opposite end of 

 the lever. 



Where must the fulcrum be 

 placed so that the two arms of 

 the lever, with their loads, will 

 balance each other? 



Now put two books at one end 

 and one at the other. About how 

 far from the end having one book 

 must you place the fulcrum? From FIG. 24. 



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