Moments of Inertia

Revision of the use of the Perpendicular axes theorem

The perpendicular axes theorem states:

IZ is the moment of inertia of the body about the Z axis

IX is the moment of inertia of the body about the X axis

IY is the moment of inertia of the body about the Y axis

A worked example
Find the moment of inertia of a uniform square lamina, of side 2l and mass M, about an axis through it’s centre of gravity perpendicular to it’s plane.
 


Y( mass) ( side divided)2 ( M)(l)2

IX( mass) ( side divided)2 ( M)(l)2

Io = IX + IY

Io ( M)(l)2 ( M)(l)2

Io ( M)(l)2
 

wsheet2.doc contains further examples for practice