CHAPTER VII. 



PARALLEL FORCES. CENTRE OF GRAVITY. 

 THE LEVER. 



13. PARALLEL FORCES. 



i. Example of parallel forces. Place the ends of a stiff lath or rod of 

 uniform thickness upon two letter balances, or support the rod by hanging 

 each end from a spring balance. Notice the load borne by each balance ; 

 then weigh the rod, and so determine the fraction of the load supported at 

 each end. 



FIG. 22. The reading of the spring balance is equal to the total weight of 

 the lath and the loads. 



ii. Resultant of parallel forces. (a) Suspend a light lath from a spring 

 balance by a ring above its centre (Fig. 22). Notice the reading of the 

 balance. Hang two equal weights in bags from the ends of the lath, and 

 again observe the reading of the spring balance. Repeat the experiment 

 with unequal weights placed in bags arranged on the lath so as to counter- 

 poise one another. Record your results thus : 



29 



