The first moment of area (about the axis) was
Similarly second moment is same but with instead of ,
Example 6.9:
Find the second moment of area under
about the
axis from
to
.
Solution:
Note: To find second moment about axis is more complicated:
This will not be done here.
Note: Recall that first moments are used in calculating centroids which are related to centres of mass.
Second moments are used in calculating moments of inertia of flat planes.