104 ON THE ACCURACY ATTAINABLE WITH 



Effective Force, the meaning of the equation can be grasped 

 even by a student whose dynamical knowledge is small. 



With the present apparatus it was found necessary to 

 determine of several times before and after each determination 

 of a ; with an apparatus of more satisfactory construction this 

 would probably be unnecessary. 



To get &, the radius of gyration, the pulley wheel was 

 removed from its position on the friction rollers and was 

 attached to bi-filar suspensions. Three separate determina- 

 tions gave &=4-221, 4-205, 4.230, giving a mean &=4-218. 

 This, with the weight P=44-0 g, and the radius p=6-194 cm.. 



fc 2 

 gives for the equivalent mass of the pulley P 2 =20-5 g. 



The inertia of the four friction rollers was found from their 

 dimensions and their weights to be one-tenth of that of the 

 pulley wheel itself. As their angular speed is less than one- 

 tenth that of the pulley, their total kinetic energy is less than 

 one-thousandth of the kinetic energy of the pulley, and has 

 therefore been left out of account in the subsequent calculation 

 of g. 



T.2 



A graphical evaluation of P-^ made in the usual way 



from the results appended, by plotting t - r against 2L+w 



a+a 



and reading off the intercept on the load axis, led to a value 

 21-2 g. 



A graphical method may also be adopted for ascertaining 

 the fraction of a revolution at the beginning in finding a, and 



at the conclusion in finding a'. If R is the number of revolu- 



p 

 tions from and to rest respectively, we have^ in each case a 



constant, and so x, the unknown fraction of a revolution, can 

 be at once obtained by plotting (0, 1, 2, 3, etc.) R against 

 TO, T\, Tl, T\, etc., where T , T 19 etc., are the times of x, 1+x, 

 2+x, etc., revolutions. In the a measurements this fraction is 



