Question

Why would anyone care about the moment of inertia of a planet?

Answer 1

We can start by defining the moment of inertia and how it is related to a planet. We know that planets move around the sun. This movement is called revolution. We can then state why the moment of inertia is important in the motion of planets.

Complete step by step solution:
Inertia can be defined as the quantity by virtue of which a body resists motion. Moment of inertia is the tendency by which the body resists angular acceleration. It is found by adding the product of all the mass and square of distance of its distance from the axis of rotation.
Moment of inertia of a planet helps us understand the composition, density and spin rate of it.
Since the moment of inertia depends on the mass, it helps us get an idea about the density of the planet. The moment of inertia of earth or any planet changes due to the glaciers or mountains as well. This changes the rotation of the earth making the day shorter or longer.
The shape of the planet can also be figured out and how much mass it has as well as what it is mainly composed of.
Thus, the moment of inertia of a planet gives us an idea about the mass, shape, density and the rotation of the planet.

Note:
The moment of inertia is important in rotational motion just as mass is important in translational or linear motion. In rotational motion, as the moment of inertia increases, the angular acceleration increases, causing the torque to increase as well.