30 



THE ROYAL SOCIETY OF CANADA 



_ ™ I mass of body x displacement 

 \ displacing force 



Jtt^ 



mass of body 



displacing force / displacement 



r, I mass of body ^ 



Experiment II. — Let the ball swing to and fro as a simple 

 pendulum and find its time of swing. Make a mark on the bench to 

 mark the central position and take the transits in one direction only. 

 Enter up every fifth transit as indicated in the table. 



Average 



Divide the average of the numbers in the last column by 30 to 

 get the period t. 



The ball dealt with above had a simple pendulum period of 3 • 76 

 seconds. 



Combination of the results of Experiments 1 and 2. 

 From t = 27: -J -j- we get 



M = 



kt2 



85x3-762 



30-5 pounds. 



^^{^ 4x9-87 



which may be one per cent low from taking g = 32 instead of 32-2, 

 and another per cent out from errors in the spring balance readings. 



Find the length of the wire supporting the pendulum. 



The wire is so long that the effective length of the simple pendulum 

 is from the point of support to the centre of the bob. Calling this L, 

 we get: 



