If that object is at rest, inertia is why it keeps sitting there, not moving, until an outside force is applied to it. If that object is in motion, inertia is why it wants to keep going in the same direction until an outside force acts on it. That is why a freight train is so difficult to stop. Inertia is also the reason a package sitting on the seat of an automobile will slide on the seat when the automobile turns. The package wants to continue in the direction it was going, even when the car has changed directions.
Rotational inertia is the inertia of an object rotating on an axis.
Like objects traveling in a straight line, rotating objects, such as tops, flywheels, gyroscopes, want to keep spinning. The rotational inertia of an object is directly related to its rate of rotation. Objects with large rotational inertia require a large force to overcome it, while objects with small rotational inertia require a small force. Click here to let me know.