# What is moment of inertia?

Moment of inertia is the resistance shown by an object to change its rotation. It is also popular as angular mass or rotational inertia of the given rigid body. One can define the moment of inertia as the ratio of the angular moment to the angular velocity of the particular object moving at its principal axis.

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## Key difference in Inertia and Moment of Inertia

Inertia is basically the property of an object which tends to resist its state of motion. It is a force which keeps the motionless object motionless and allows the moving object to move at the current speed. The larger inertia of the object, the greater force you need to change the velocity in a given time. Let’s take a common example; assume a big truck and a small car to be at rest.Here we need a greater amount of force to move the truck at a certain speed. But in the case of the car, we require less amount of force to push the small car to that same speed at that particular time.

Likewise, the moment of inertia is the property where the object resists change in its position of rotatory motion. With greater the amount of moment of inertia, we need a large amount of torque to have the same change in its angular velocity at a particular time.

Unlike inertia, the moment of inertia depends both on the mass of the object and the distribution of mass about its axis. The value of the moment of inertia may vary with respect to the different axis.  To rotate an object at different axis with the same angular velocity, you need different torque.

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### Properties of Moment of Inertia

One can determine Moment of inertia as a tensor quantity. This means that it has different values for the different axis.

MOI entirely depends upon the mass of the object and its mass distribution around its axis.

Every object can have different values of MOI about its different axis

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It is the basic property of every matter which maintains the angular motion. This is only applicable till one applies external torques on it.

One can define it as the additive property of the matter. On featuring a complex system, the moment of inertia is the sum of objects subsystems. (The point is that all should be on the same axis)