Calculating force to bend a rod?

[MrForbes]

Kevin--I suggest you get the students to calculate moment of inertia for several different cross sections, including a flat bar in both X and Y orientations...then let them play with the formula for stress due to bending, and see how the stress varies with the different sections and orientations.

I spent some time with a few students during build last winter, I think they learned these concepts well enough to develop a good understanding of why the lightening holes should be on the sides.

Also Ken, the modulus of elasticity is pretty much the same for all flavors of aluminum, the alloy doesn't affect it enough to worry about it for the calcuations we make.