340 SOME SIMPLE MACHINES IN THE HOME 



six inches, and the circumference of the circle described by 

 the hand in operating the handle is sixty inches, then the 

 resistance of 200 pounds at the roller would require you to 

 expend only twenty pounds at the wringer handle. Ex- 

 press this in terms of the law of machines. 



Wheels of different diameters connected by belts or 

 interlocked by gear teeth are used for the purpose of 

 changing speed as well as for the reason of mechanical 

 advantage. A study of a few home machines will make 

 this apparent and explain the purpose of their use. 



Experiment. To illustrate changing speed by use of wheels of different 

 diameters joined by belt or gears. 



Materials: A Dover egg beater, or drill with gear and wheels. Bicycle. 



Method: (A) Mark one point on the working part of the egg beater. 

 Observe how many times this revolves for one complete turn of the 

 handle. Try this three times. (B) Count the number of cogs on the 

 two wheels which connect the force end of the machine to the work end. 

 What is the relation of the numbers of cogs? (C) Make similar com- 

 parison of the cogs on the rear axle and on the sprocket wheel of your 

 bicycle. Find the number of revolutions of the rear wheel to one 

 revolution of the crank. What general rule regarding change of speed 

 is suggested to you by these observations? 



The sewing machine. A great many other types of 

 machines can be found in our homes, but one almost al- 

 ways present is the sewing machine. Since 1850 these 

 machines have been improved more and more, so that 

 now their work is extremely rapid and efficient. A study 

 of the part that does the stitching is somewhat too com- 

 plex for us at the present time, but would make a very 

 interesting home project' which could be studied by means 

 of diagrams furnished by almost any good machine supply 

 house. One good project which could be worked out in 

 the laboratory would be to find out how power is trans- 



