# What is the second moment of area?

1. Apr 28, 2010

### mzha109

Hi I'm a second year uni student and we're learning the engineering beam theory, and part of the engineering beam theory requires us to know what the second moment of area is. I've scrawled wiki and the internet but I haven't found anything very helpful.

So my question is, what exactly is the second moment of area?

2. Apr 28, 2010

### Rajini

3. Apr 28, 2010

### mzha109

That's not particularly descriptive.

And also, the definition of the second moment of area is I_{yy}=\int_A z^2 \, dA

But why is the lower limit of intergration A, and there is no upper limit?

4. Apr 28, 2010

### Rajini

A is not the limit! In that case the integral symbol represents the area of the region A.
It is some part of the cross-section of the beam.

5. Apr 28, 2010

### mzha109

*face palm*

Thanks, I might have some more questions in the near future but I'm done for now.

6. May 4, 2010

### mzha109

Hey one more question about the second moment of area. How do you find it for any shape and about any axis? I'm still rather confused about the integral thing and it'd be helpful if someone went through the process of getting the second moment of area step by step.

Thanks.