356 



Introduction to the Study of Science 



point D lines parallel to the lines representing the strings of B and C 

 balances. Measure two adjacent sides and compute their numerical 

 value by your scale. Do they agree with the recorded readings of 

 the balances? Do they correspond with the results you obtained in 

 the case of , Fig. 121? 



Change the direction in which balance A is pulled in order to pro- 

 duce results similar to those brought out in the study of the wagon. 



Draw each typical example ac- 

 cording to scale and compute 

 the magnitudes represented by 

 the proper sides of the figure. 

 Do the experimental results 

 agree with the results of con- 

 struction to scale ? If the 

 method and results are not 

 clearly understood, they should 

 be considered carefully and 

 tried experimentally until they 

 become perfectly clear. Vary 

 at will the position of the string 

 of the pulling balance on the 

 string connecting balances B 

 FIG. 123. Arrangement of spring bal- and C, and make new problems 

 ances to show the relation of a resultant to for the several trials, 

 its component forces, or of a single force to Exerc ise. How are forces 

 its resolved lorces. , v i 



measured r In what ways may 



they be expressed ? How may they be represented ? What characters 

 of force may be represented graphically? 



In order to test the value of the method and its application to cases 

 where a given force is broken up or resolved into two forces, the one 

 effective and the other wasted, we may take a problem similar to 

 those studied, namely the towing of a ship through a canal, Fig. 124. 

 A ship is towed by an electric tractor. The tractor exerts a direct 

 pull upon the towline of 1000 pounds. The towline pulls the ship 

 not only ahead, but also toward the bank of the canal. The pull 

 toward the bank is counteracted by the shape and position of the 

 ship's hull and by the rudder. What, as represented in Fig. 125, 

 is the amount of each of the resolved forces ? Let the towline be 

 twice as long, as shown by the dotted lines. What do you find to be 

 the magnitudes of the resolved forces? 



Suppose the tractive or pulling force is 800 pounds, and the angle 

 formed by the towline with the line representing the path of the 



