DEFINITIONS AND MECHANICAL PRINCIPLES If]. 



way, as it is equal to the number of strands supporting 

 the weight. This will agree with the former method 

 when the power is acting downward. If the power is act- 

 ing upward instead of downward, the power strand would 

 be supporting the weight, and so should not be deducted 

 from the total number to obtain the mechanical advantage. 

 Fig. 5 illustrates a tackle which has six strands, but 



FIG. 5 A TACKLE. A 

 FORCE MAY BE 

 MULTIPLIED MANY 

 TIMES BY A TACKLE 

 OF THIS KIND 



FIG. 6 DIFFEREN- 

 TIAL TACKLE BY 

 WHICH HEAVY 

 WEIGHTS MAY BE 

 RAISED 



only five are supporting the weight, so the mechanical 

 advantage in this case is five. If the weight be 1,000 

 pounds, as marked, a force of 200 pounds besides a force 

 sufficient to overcome friction will be needed to raise the 

 weight. This tackle has a special designed sheave which, 

 when the free rope end is carried to one side and let out 



