Inertia of a body is its inability to change by itself its state of rest or of uniform motion in a straight line. Similarly Moment of inertia of a body is its inability to change by itself its state of rest or of uniform rotatory motion about an axis.
The formula for Moment of Inertia of a rigid body is given as,
The moment of inertia of the rigid body (l) = Sum of moments of inertia of
all the particles present in the body.
Let us consider,
m1, m2, m3 = masses of large particles in a rigid body
r1, r2, r3 = distance of the masses from the axis
The formula for Moment of Inertia of a rigid body will be,
l= m1r12 + m2r22 + m3r32 + …
The above formula can also be expressed as,
mi = mass of ith particle
ri = distance between ith particle and axis o rotation