**First Moments of Area:** As the name
implies, first moment of an area is calculated by taking the moment
of an area about a particular axis. For example, consider an
arbitrary area A shown at right. Its
first moment of area about the designated x axis is given as

(1) |

where y is the perpendicular distance measured from the x axis to the centroid of the differential area dA. Similarly, the first moment of area about the y axis is given as

(2) |

The first moments of area are used extensively in mechanics of materials for calculations of flexural shear stress components.

The calculations of first moments of area are demonstrated in the following example.