parallel axis theorem

parallel axis theorem (uncountable)

1. (physics) A theorem that states the moment of inertia of a rigid body about any axis is equal to its moment of inertia about a parallel axis through its center of mass plus the product of the mass of the body and the square of the distance between the two parallel axes.

Let I_cm be the moment of inertia of a rigid body about an axis through the centre of mass of the rigid body. The parallel axis theorem states that the moment of inertia of the body about some other axis parallel to the first axis equals ${\displaystyle I=I_{\mathrm {cm} }+md^{2}}$, where m is the mass of the rigid body and d is the distance between the two parallel axes.

• perpendicular axis theorem