# Moment of inertia of a point mass

1. Sep 16, 2013

### geekie weekie

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. Sep 16, 2013

### Staff: Mentor

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

3. Sep 16, 2013

### namanjain

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

it's at r dist from rod

I=mr2

4. Sep 17, 2013

### Vphysics2013

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.

5. Sep 17, 2013

### sophiecentaur

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.