Section Properties of Slender Rod Feature Calculator and Equations.
In physics and applied mathematics, the mass moment of inertia, usually denoted I, measures the extent to which an object resists rotational acceleration about an axis, and is the rotational analogue to mass. Mass moments of inertia have units of dimension [mass] × [length]2. It should not be confused with the second moment of area, which is used in bending calculations.
For simple objects with geometric symmetry, one can often determine the moment of inertia in an exact closed-form expression. Typically this occurs when the mass density is constant, but in some cases the density can vary throughout the object as well. In general, it may not be straightforward to symbolically express the moment of inertia of shapes with more complicated mass distributions and lacking symmetry. When calculating moments of inertia, it is helpful to exploit the properties of the moment of inertia, namely it is an additive quantity and the parallel axis theorem, and perpendicular axis theorem.