314 PRACTICAL MATHEMATICS 



If I is the moment of inertia of the circular section about the 

 axis of the cylinder, 



Then I = ? 



a 



, _, 7T7"^ ., 



and T = 



NOW e = ^ 



r 



l_ 2T 



2/T 



radians 



A' 



= ^ radians 



Let the cylinder be hollow, and let r l and TI be the internal 

 and external radii respectively. 



Then 



T= :r/ s 



r z J 



2 ~" ^n 



7T 

 16 i* 2 



where d 2 and d x are the external and internal diameters respec- 

 tively. 



If I is the moment of inertia of the section about the axis of 

 the cylinder, 



