Moment of Inertia

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The best way to understand Inertia is by comparing it to mass. What mass is in a linear system, Inertia plays the same role in a rotational system.

When dealing with rotational systems it is very important to move over the understanding of a linear system as it gets difficult to understand concepts of rotational motion. Moment of Inertia or Inertia is the property of a body that is dependent upon the mass of that body, its dimensions.

Unlike mass which is constant irrespective of the shape of the body (assuming differently shaped bodies have the same mass), the moment of inertia changes when you change the axis about which you’re rotating the body.

Even if you keep the mass the same but change the shape of the body, moment of inertia changes.

Let’s take the example of a table fan. Assuming all the energy generated by the rotation of the blades gets converted into kinetic energy of the wind generated by the fan.

Now consider two types of blades in the fan. Both have the same mass but different shapes. One blade is such that most of its mass is focused on the central axis and the other is such that most of the mass is focused on the outer radius.