Momentum and Energy


What plays the role of mass in rotation?

Mass is defined as the net force on an object divided by its acceleration. By analogy, then, the property that takes the place of mass should be the torque divided by angular acceleration. The property is called rotational inertia or the moment of inertia. It depends not only on mass, but on how far the mass is from the axis of rotation. The further the mass is from the axis, the larger the moment of inertia. If you sit on a swiveling stool or chair while holding heavy weights, the further you extend your arms, the more difficult it is for someone to start you rotating. That is, it will require more torque to achieve the same angular acceleration.


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