This document defines moment of inertia and related concepts. Moment of inertia is a measure of an object's resistance to changes in rotation and is used in strength of materials calculations. It is the sum of the area of each component multiplied by the square of its distance from the axis of rotation. Related concepts explained include center of gravity, centroid, second moment of area, and formulas for calculating moment of inertia for simple shapes.

1. Lecture Series on
Strength of Materials-5
“Moment of Inertia”
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2.  Centre of Gravity
 It is defined as the point through which
whole weight of body supposed to be act.
 Centroid or Centre of Area.
 It is defined as the point through which
whole area is assumed to be concentrated.

3.  It is defined as the algebraic sum of product
of area and the square of distance from the
particular axis.
 It is denoted by Ixx or IYY
 It is given by I=Ah2
 Unit- mm4.
 It is second moment of area which is
measure of résistance to bending & forms
basic to strength of material.
 Mass MI is the résistance to rotation & forms
basic to dynamics to rigid bodies.

4.  It is defined as the distance at which area is
supposed to be concentrated for same
moment of inertia.
 It is denoted by K.
 It is given by ;I= Ak2 K= (I/A)1/2
 Unit-mm.

7.  M.I of plane section
about any axis is
equal to MI of plane
section about the
parallel axis parallel
axis passing through
its CG plus the
product of area and
square of distance
between two axes.

8.  The moment of
inertia of polar
axis is equal to
algebraic sum of
MI of two axis
about which axis
is perpendicular.

13. Thank You