Lew Hodgett wrote:

Depends on the vertical height of the side and rear panels.

The larger the height value, the stiffer the box.

Some basic strength of materials.

I (Moment of Inertia) = (b*h^3)/12
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Bill wrote:


Are you saying that *sag* is related to a rotational force?

Concerning "sag", it seem like we should be measuring the
distribution of mass between supports. If F=md is the force in the
middle (of the horizontal beam) and it is low, then we should
experience less sagging, right? The "trick" seems to be to make sure
d is small. h appears to have little to do with it. Not being an
engineer, I only have a very basic grasp of the concepts.
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The math confirms the following.

A 2by4 supported at each end will be stiffer if the 4" side is
vertical
rather than the 2" side.

The taller a vertical panel is the more "sag resistant" it is.

That's why the face frame is so important for case goods or the
apron for a table.

It is also why 1/4" plywood panels nailed to the studs at the corners
of
a building makes the building far more earthquake proof.

Lew