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Define moment of Inertia

  1. Mar 18, 2015 #1
    I've been studying rotational motion for a while and I have no clue how moment of inertia plays a role in it. How would you define it? Often times, it's just described as resistance to change. Does that mean a high moment of inertia means a higher resistance to change or is it the other way around? I need more conceptual explanations than mathematical explanations so I can understand better. Thanks in advance!
  2. jcsd
  3. Mar 18, 2015 #2


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    Staff: Mentor

    I think wiki's definition is pretty straightforward: The moment of inertia or angular mass of a rigid body determines the torque needed for a desired angular acceleration about a rotational axis. It depends on the body's shape, mass distribution and chosen axis, with larger moments requiring more torque to change the body's rotation...

    In other words, the larger the moment of inertia, the more torque is required to accelerate it to a given angular velocity.
  4. Mar 21, 2015 #3

    Suraj M

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    Gold Member

    In simple words, its equivalent to mass in rotatory motion, which you already know.
    Take a short iron rod and try lifting it from one end, pretty easy, now take a pipe of almost same mass but very long, try lifting it from one end, definitely more difficult, thought it's the same mass, this would mean that there's something else that matters other than mass that decides the work you need to do to execute the task.
    Moment of inertia just includes that.
    see if this helps
  5. Mar 21, 2015 #4
    See the attached sheet for the connection between linear mass and rotaional mass of inertia with regard to newtons rules of motion, this might help.

    Attached Files:

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