# Difference Between Young's Modulus & Second Moment of Area

1. Nov 2, 2018

### tomtomtom1

Hi all

I was hoping someone could help explain the difference between Young's Modulus and Second Moment of Area.

I know that Young's modulus is a measure of how elastic a material is and is calculated by Stress/Strain.

I know that the Second Moment of Area can be defined as a objects resistance to bending.

But if I had a material that had a high Young's Modulus meaning that it was less elastic in other words more stiff then isn't that the same thing as the second moment of area?

Can anyone see where I am coming from?

I know the two are related but to me they seem like they are describing the same thing?

The only difference I can see is that Youngs Modulus describes stiffness in terms of elongation/compressions whereas the second moment of area describes bending/deflecting.

Can someone explain or define the concepts if I have it wrong?

Thank you.

2. Nov 2, 2018

### PhanthomJay

Young’s modulus E and the second moment of area, I, usually call Area Moment of Inertia, are not at all related. E Is an intrinsic property of the material, while I is a geometric property of the area of its shape. You can have a beam with a high E but a small I , and the beam may not be very stiff at all in bending deflections, like a steel rod for example. The stiffness or rigidity of a beam of a given length is is EI. When both E and I are relatively large, deflections are small compared to low E and low or high I , or low I and hi or low E.

3. Nov 3, 2018

thank you.