Hi all,

Today's post is about designing a collegiate level course in popsicle stick bridge building. The idea has been in my head for years, but the post today is inspired by a friend who asked if I'd speak to his son's Scout Troop about engineering. Ideally, I could propose an engineering related activity for the kids. Naturally, I'd already given extensive thought to the whole thing.

Here it goes.

## Intro

There's a joke, that I've updated slightly to address #metoo concerns, about a mathematician and an engineer. They're both offered a scenario, we'll say a hallway with a candy bar placed at the far end, and they're told they can move half the distance down the hallway towards the candy bar. They can keep moving half the distance, and if they reach the candy bar, they can eat it.

The mathematician says "That's impossible. You will asymptotically approach the candy bar, but you will never reach it."

The engineer says, "Well, you can get close enough."

The point is that engineering, while steeped heavily in math, also acknowledges the practical messiness of trying to perfectly model the world we live in, and seeks practical applications of math to build real world solutions. (Related: I recently learned the phrase "All models are wrong, but some are useful" which I really like.)

## The Real World is Messy

The real world messiness really hit home for me when I was junior engineer and got curious about how stress limits were determined in certain types of steels. While a single handbook number might seem to provide a comforting level of confidence in it's simplicity, under the hood, there are variations in the steel from batch to batch, there is uncertainty in the dimensional accuracy of the test specimens used to calculate the stress, and there is uncertainty in the force and displacement measurements used to calculate stiffness and strength (which combined with the dimensions, leads to stress measurements).

Smart people with Phd's, who sit on committees, take that statistical distribution of actual steel strengths, and provide a number that can be used for design, in combination with appropriate load factors and safety factors, to yield something that is practical and safe. And yes, depending on the application and circumstance, it may be appropriate to qualify the particular batch of steel or other material being used on a project by testing.

## Course Goals

So my goals for an engineering course would be to teach an appreciation for this real world messiness, while showing how engineering principles are used to safely arrive at solutions that are "close enough." I'd also want it to be hand on, fun, accessible for freshman/sophomore students (or advanced high schoolers), and finally, needs to use either popsicles, or marshmallows and toothpicks.

## Unit 1: Basic Statics and Strength of Materials

In the first unit, we'd learn about the different failure mechanism for popsicle sticks, and popsicle stick joints.

We'd learn about kinematic constraints, and experiment by constraining and then loading popsicle sticks to the point of structural failure. We could experiment with bending failures, compression failures, shear failures, and torsional failures. We would then build an empirical understanding of the strength of a popsicle stick.

In the second half of the the unit, we'd build an understanding of the strength of a popsicle stick glue joint, both in shear, in tension, and under bending loads.

We'd learn about the statistical distribution of failures and also have a ton of fun breaking a whole bunch of popsicle sticks.

## Unit 2: Design and Analysis

In the second unit, we'd design popsicle stick structures on paper, then analyze them. We'd take calculated loads and appropriately double or triple the popsicle sticks where needed, or otherwise alter the designs.

Finally, in the last half of the unit, we'd test our designs to a required load, and finally, load them to failure to see if they break where and how expected.

For bonus points, we could add additional constraints to the design, including cost factors on glue and the number of popsicle sticks used. More cost effective designs would win.

## Toning This Down for Scouts

Of course, I wouldn't expect a bunch of grade school kids to follow along to learn the matrix displacement method for analysis of statically indeterminate structures (I'll admit, it's been a while since I've worked in that branch of engineering, and I Googled that), but I do think we can have fun maybe measuring how much force it takes to break some popsicle sticks laid flat across a short span, then making predictions about how many we'll need to hold up a 15 lb weight.

## Thoughts On Other Courses

I've also thought about extending these ideas to other domains, especially Electrical and Computer Engineering, starting with simple transistor circuits, building up to basic logic gates, then to registers, counters, and more sophisticated structures, understanding what goes into a microchip, progressing to assembly language, then C/C++, gradually moving up the stack to operating systems and networking, and then to higher level languages, applications, and architectures. This is exactly the idea behind https://www.nand2tetris.org/, so I'm not the only one that feels this way.

Anyway... that's all for now. I still have book reports, BOM Scrubs, Vickrey auctions, and more on my mind.

Cheers!

Sam

aka THE Awkward Engineer