Question

For Problem 18.20 in Beer's text Dynamics, is the product of inertia positive in both the xz and xy planes? Our instructor has Ixz being positive...

Answer 1

A product of inertia is obtained from an integral over an area by multiplying the product of the coordinates x and y about the reference coordinate axes by the elemental area.

Similarly,

Unlike the moment of inertia, although the elemental area is positive, the product of inertia can be positive, negative, or zero because the value of the coordinates x and y can be positive, negative, or zero.

So product of inertia can be positive or negative as per your choice of coordinates.

answered by: anonymous