
In rotational mechanics, the moment of inertia (MI) is similar to mass in linear motion. The mass resists a change in translational motion, and the moment of inertia resists a change in rotational motion. It depends on the distribution of mass relative to the axis of rotation. The moment of inertia of a cone differs depending on the axis chosen, because the mass distribution relative to each axis changes.
A cone is a three-dimensional solid with a circular base and a pointed tip called the apex. To calculate its moment of inertia, we need to consider how its mass is spread along its height and base.
Considering a solid cone of mass M, radius R, and height h, the moment of inertia is calculated for two cases.
The following are the two cases:
The axis is taken along the cone’s height. The perpendicular distance of each mass element from the axis is its radial distance. Divide the cone into thin circular disks stacked along the height.


Using the perpendicular axis theorem and parallel axis theorem, the axis is shifted using the parallel axis theorem.

Considering a hollow cone of mass M, radius R, and slant height l.
Here, the moment of inertia is calculated along the symmetry axis because all surface elements are at the same perpendicular distance R from the axis.
Surface area of cone = π R l
Iaxis = M R2
Therefore, the moment of inertia of a hollow cone along the symmetry axis is: M R2
| Shape | Axis | Moment of Inertia |
|---|---|---|
| Solid Cone | Symmetry Axis | ![]() |
| Solid Cone | Central diameter of base | ![]() |
| Hollow Cone | Symmetry Axis | M R2 |

Q1. Why is the solid cone's moment of inertia smaller along the height?
In a solid cone, most mass is near the base; hence, the moment of inertia along the height is relatively small. Hollow cones have larger MI because all mass lies far from the axis.
Q2. Why is the parallel axis theorem important for cones?
It allows calculation of MI about axes not passing through the centre of mass, such as the diameter of the base.
Q3. Why do rockets and missiles often have cone-shaped tips?
The cone shape reduces air resistance, and knowing its MI helps engineers control spin and stability during flight.
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