Moment of inertia of a point mass

  1. Hello,

    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. DrClaude

    Staff: Mentor

    It is a distance, expressed in units of length (meters in the SI).
  4. __________________________________________________________________________

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

    it's at r dist from rod

  5. 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. sophiecentaur

    sophiecentaur 14,712
    Science Advisor
    Gold Member

    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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