1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is this a correct derivation of Moment of Inertia?

  1. Jul 21, 2013 #1
    Hello everybody!
    This is the derivation (for a single particle).
    \tau = F_{\perp }r
    \ = ma_{\perp}r
    \ = \alpha mr^2 \\
    \text{if }\
    \tau = I\alpha
    \text{ where } I \text{ is resistance to accleration then } \\
    I = mr^2
    I'm curious what the problem with this is because I haven't seen it in any of my physics texts (serway and university at least). I also haven't seen it on the interwebs very much.
    Thanks for reading.
  2. jcsd
  3. Jul 21, 2013 #2

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    Moment of inertia refers to the ratio of the torque to angular acceleration of a rigid body about an axis. It is the inertial resistance to rotation that a rigid body has about a specific axis of rotation. A single particle is not a rigid body.

    What you are doing is determining the ratio of torque to angular acceleration of a single point particle about an axis of rotation.

    If you were to reduce a rigid body to a collection of single point particles of mass dm and add up all the dmr2 terms where r is the distance from the point particle to the axis of rotation, you would end up with the moment of inertia of the rigid body.

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Is this a correct derivation of Moment of Inertia?
  1. Moment of Inertia (Replies: 3)