# Calculation of the moment of inertia

1. Jan 16, 2012

### Dranzer

I was wondering why we can not always assume the mass of a body to be concentrated at the Center of Mass and then multiplying the total mass by the square of the distance from center of mass to the axis,while calculating the moment of inertia of a body.(I found this question in University Physics)

Thank you.

2. Jan 16, 2012

### Naty1

Hi Dranzer:

http://en.wikipedia.org/wiki/Moment_of_inertia

3. Jan 16, 2012

### Dranzer

Thank you very much.I didn't quite think of that.

4. Jan 16, 2012

### sophiecentaur

It's interesting to note that the MI relates to the Standard Deviation of a statistical distribution and also to the strength of a beam. They're all 'second moments'.
Same maths crops up all over the place.

5. Jan 16, 2012

### meldraft

An interesting thing to add though, is that the second moment of area only depends one the geometry of the cross section, while the mass moment of inertia also depends on the actual mass.