Polar moment of inertia

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A schematic showing how the polar moment of inertia is calculated for an arbitrary shape about an axis o.  ρ is the radial distance to the element dA.
A schematic showing how the polar moment of inertia is calculated for an arbitrary shape about an axis o. ρ is the radial distance to the element dA.

Polar moment of inertia is a measure of an object's ability to resist torsion. It is required to calculate the twist of an object subjected to a torque. It is analogous to the area moment of inertia, which characterizes an object's ability to resist bending and is required to calculate displacement.

The larger the polar moment of inertia, the less the beam will twist, when subjected to a given torque.

The polar moment of inertia must not be confused with the moment of inertia, which characterizes an object's angular acceleration due to a torque.

See also moment (physics).

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