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Moment of inertia of a point mass

  1. Sep 16, 2013 #1

    This is a very basic question. Wikipedia says moment of inertia I of a point mass m is calculated as:

    I = m * r^2

    Where, r is distance from the axis of rotation. What this actually mean? I mean what is an r?
  2. jcsd
  3. Sep 16, 2013 #2


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    Staff: Mentor

    It is a distance, expressed in units of length (meters in the SI).
  4. Sep 16, 2013 #3

    this is axis of rotation and in front ist point mass not full stop .

    it's at r dist from rod

  5. Sep 17, 2013 #4
    moment of inertia of a point mass with respect to an axis is the product of mass times the distance of the axis
    squared.So "r" is the distance of the mass "m" from the axis of roation.
  6. Sep 17, 2013 #5


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    Science Advisor
    Gold Member
    2017 Award

    Moment of Inertia of an object has to be referenced to a particular point or axis. Take any object and its MI is a minimum when that reference is through the CM. For a point mass, it is Zero.
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