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Moment of Inertia is defined for any body about any axis.

The moment of inertia is used to do calculations for angular momentum or torque required to rotate the object at a required angular speed or acceleration.

It is useful in rotational mechanics.  Moment of inertia exists for any body about any axis.

If the objects do not rotate then  linear quantity of the body - mass - is used for calculating the needed physical quantities.

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Moment of inertia is the name given to rotational inertia, the rotational analog of mass for linear motion. It appears in the relationships for the dynamics of rotational motion. The moment of inertia must be specified with respect to a chosen axis of rotation. For a point mass the moment of inertia is just the mass times the square of perpendicular distance to the rotation axis, I = mr2. That point mass relationship becomes the basis for all other moments of inertia since any object can be built up from a collection of point masses