The **moment of inertia** (symbol *I*, SI unit kg·m^{2}) of a rotating object is a measure of what angular acceleration will be produced by a given torque, and can therefore be thought of as the rotational equivalent of mass. It is defined as

- $ \iiint \rho (r) r^2 dV $

For a point mass, it is equal to the distance from the centre of rotation squared times the mass of the object, or

- $ I = mr^2 $

The moment of inertia is also equal to angular momentum divided by angular velocity, or

- $ I = \frac{L}{\omega} $