pic: REV Robotics building system

[EricH]

Originally Posted by Lireal

Can you be a little more clear? Which has less deflection, the tubing or the extrusion?

Just to be a total annoyance (and to give you a taste of real engineering):

What's the load case, the size, and the wall thickness? Oh, and how is it supported? You see, the answer depends on knowing those... OK, OK, I'll go a little easier than that.

What he's saying is, essentially, more material at the outside of a piece of material will resist deflection better, given the same mass and size. BUT, extrusion may be tailored to resist deflection better in one direction. (I-beam being one example--it'll bend better if you're trying to bend it in the direction of the open sides than if you try to bend it towards the flanges.)



Moment of inertia (and in this case, that's MASS moment of inertia) is something you'll tend to hit somewhere around 2nd-year engineering coursework, possibly a hair sooner. It's not that hard in concept; the simple definition works out to how much torque it takes to rotate an object about a given axis. Now, the actual application of that definition, and the formulas to help determine it, are where that gets fun, as the shape of the object in question plays a role (which is why that was brought up in the explanation). If you're interested in running through some of the math, let someone know; that can be arranged...