**MODULUS**** OF ****ELASTICITY****: **The ratio of stress to strain or the stiffness ofÂ the material of a structural member (resistance to deformation).

Essentially, the **modulus** of **elasticity** is a more general term regarding the overall stiffness of a member.Â

Â E= Modulus of Elasticity. If E increases, then so does the stiffness.Â

**MOMENT OF INERTIA: **The bending stiffness of a structural member’s cross-sectional shape.

Â Moment of inertia is specific to bending of the cross section of the member .Â

**SECTION ****MODULUS****: **The ratio of the maximum moment on a beam and the maximum fiber stress (or moment of inertia over distance to nuetral axis of the member).

The section **modulus** is used to to find the minimum required beam that will support the bending load by looking in tables provided, such as in the Manual of Steel Construction.

bd^{2}/6

[source: http://ironwarrior.org/ARE/General_Structures/]