64 LABORATORY EXERCISES 



the brace once. How many times as great as the distance 

 between threads is the circle "described" by your hand? If 

 you exert a force of 1 kg. on the brace, how much do you exert 

 on the screw threads? 



EXERCISE 61 

 WHEEL AND AXLE 



Apparatus and Materials. Wheel and axle (usual form) or a wheel- 

 barrow, cord, tape, books or weights. 



a. Set up a wheel and axle as shown in Fig. 178, 202, of the 

 text. Wind the cord about the wheel so that it will unwind at 

 the same time that the cord on the axle is wound up. What 

 is the diameter of the wheel? Of the axle? How many grams 

 tied .to the cord that is attached to the wheel will just balance 

 100 g. on the cord attached to the axle? If you attach one book 

 to the wheel, how many books of the same weight will it support 

 on the axle? 



b. Another form of the apparatus can be made out of a 

 wheelbarrow. Turn the wheelbarrow upside down, over a box 

 or some saw horses if possible, so that the wheel will be at least 

 45 cm. (about 18 in.) from the floor. 



A stout cord tied to the inner end of one of the wheel spokes 

 is to be wound upon the ' ' hub." The hub serves as the ' ' axle " 

 of the apparatus. A tape may be tied to the rim of the wheel, 

 so that the free end of the tape is wound up at the same time 

 that the cord on the hub is unwound. 



What is the diameter of the wheel? What is the diameter of 

 the hub at the place where the cord is attached to it? How 

 great a weight, tied to the hub cord, can be supported by 1 kg. 

 tied to the wheel tape? Try the experiment, using several 

 books of equal weight if you have no metal weights. 



