350 



OUR PHYSICAL WORLD 



multiplied 500 times, ignoring friction. If one were pressing, 

 therefore, on the handle with a pressure of 20 pounds to turn the 

 nut, the bolt head would be drawn toward the nut with a pull of 

 5 tons. 



FIG. 193. A wrench used to turn the nut on a bolt 



Examine the machines that are commonly seen, the sewing 

 machine, locomotive, automobile, typewriter, etc., and you will 

 find they are made up of ingenious applications and combina- 

 tions of these three simple machines so arranged as to accomplish 

 the desired end. The elements that enter into any mechanical 

 invention are few and simple, but the possible combinations 

 and variations in the form of these elements are bewilderingly 

 numerous. 



