The Rotational Inertia or Moment of Inertia ($I$) of an object is a scalar quantity that measures the resistance of that object to changes in its rotational velocity about some axis of rotation. It serves as the rotational equivalent to mass.

For a system modeled as a single point particle, the moment of inertia depends strictly on the particle's mass $m$ and its position relative to the axis of rotation.

Let $r$ denote the perpendicular distance from the axis of rotation to the point mass. The rotational inertia is defined as the product of the mass and the square of this distance:

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