60 LABORATORY EXERCISES 



a. Open the blade of a jackknife and show that the blade 

 itself is a lever. What is the force to be overcome in opening 

 the knife? If the springs were equally strong, and the dis- 

 tances from the rivets (fulcrums) to the springs were equal, 

 which blade could be opened more easily, a long one or a short 

 one? 



b. With a pair of scissors or shears try to cut a match stick. 

 Where must you place the stick in order to cut it most easily? 

 Why? 



c. Examine several of the ''openers" used for opening "tin" 

 cans, and find one that is a lever of the first class. Describe it. 

 Find one that is of the second class. Describe it. 



What kind of a lever is a full suit case when you are trying to 

 close it? 



d. Suppose that you stand on the outside of a closed door, 

 and that your brother is on the inside trying to hold it shut. 

 If you push against the knob, and he against the middle of the 

 door, what kind of a lever is the door, so far as you are con- 

 cerned? What kind of a one is it so far as he is concerned? 

 Suppose he pushes against the knob, where ought you to push 

 to get the greatest advantage? 



e. Find out from a carpenter how to drive a nail into a board. 

 How should the hammer be held? Why? How should the 

 nail be held? Why? Drive the nail partly into the board, then 

 draw it out. Find out how to do this properly. 



/. Ask to see the construction and operation of the nail 

 extractor used in opening large packing boxes, such as those of 

 a dry goods store. Describe it. 



EXERCISE 58 

 PULLEYS 



Apparatus and Materials. Pulleys or casters, string or tape, books 

 for weights. 



