Class 11 Physics Rotational Motion | Theorem of parallel axis |

Theorem of parallel axis

__Parallel Axis Theorem__: The moment of inertia of a body about any axis is equal to the sum of the moment of inertia of the body about a parallel axis passing through its centre of mass and the product of its mass and the square of the distance between the two parallel axes.

- This theorem is applicable to a body of any shape.

Example: Given the moment of inertia of a disc of mass M and radius R about any of its diameters to be MR^{2}/4, find its moment of inertia about an axis normal to the disc and passing through a point on its edge

Solution:

We can apply Perpendicular axis theorem here on *x* axis & *y* axis and get I’, moment of inertia in *z* axis.

I* _{z}* = I

Now we can apply parallel axis theorem to find I’’.

I’’ = I’ + MR^{2 }= 3/2(MR^{2})

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