Inquiry Stylee: Castle Siege

I enjoy this lesson a lot. Actually, I’m not really sure that it’s a lesson, more like unit module search for the tri-force learning circus. Yes, learning circus. <digress>Maybe inventing my own edu-jargon and refusing to use anything else will destroy the edu-jargon beast as a whole…? </digress>

Is this learning circus new? No. Many of you do some sort of catapult type unit. I’m just asking you to loose the reigns a bit.

So, it should be apparent that I go through the physics curriculum in what ever order I see fit, which means that I don’t get to kinematics until much farther into the course than most. The kids know Issac’s 2nd and they are BFF’s with energy conservation. I basically just add new forces and energies into the mix like someone making a fantastic soup. Algebra-Calculus-Physics soup! There’s a dollop of cream cheese on top (that’s Hamiltonian mechanics) and some sprigs of chives (That’s vectors). It’s delicious and nutritious!

So, at this point I can introduce Hooke’s law as the first real variable force. All of the forces they’ve seen up until this point have been pushes, pulls, or figured from some formula that we logically figured out (e.g.: the friction equations, and weight). Hooke’s law is truly goofy in that it changes value during a problem. This throws a certain kind of kid for a loop: that child that loves to memorize. That child that brings in the formula sheet with a 5-point-font transcription of every chapter in the book. They have no concept of how physics uses math to describe the real world, that kid is a product of a whole lot of boring math lessons. It’s not that they don’t want it, it’s that they don’t even know that things could be different. This is why we must use SBG, or something functionally equivalent, to ensure that kids care about learning rather than points.

My grand idea for having some fun with elastics came from a bit of Monty Python. The scene where the French are throwing things (cows, chickens) at Arthur really stuck with me. I thought, wouldn’t it be great for my kids to siege each other?

Shoebox-Castle Warfare:

At the beginning of the year I put out an all-points bulletin for shoe boxes. We get about 500 stacked up around the perimeter of my room (this is a math lesson in and of itself) and then it’s go time. The build up is nearly irresistible.

They ask, “What kind of weapon should we make, Mr Cornally?” They ask

“Whatever one will wreak the most havoc, my little cherub.”

This is exactly the kind of question that gets us at a whole boat-load (link’s not safe for work) of physics, without me having to play dentist for even one second. What castle structure will be the strongest? What kind of catapult/trebuchet/ballista should we build? How will we know how far the ball will fly? I provide them with tennis ball projectiles and some of those awesome physical therapy elastic bands (which roughly obey Hooke’s law). Ask your gym/health teacher, they probably have a whole roll; my football coach *cough*three-peat-state-champs*cough* had close to 75 yards of the stuff I could just cut off of.

These natural questions led to kinematics and Hooke’s law. As they arose I would call a timeout and we’d play a quick session of notebook. They’d let me know when I’ve gone far enough, and then back outside they went. Most of them wanted to build the standard water-balloon launcher. This requires three people and some serious strength. Others built catapults using meter sticks, elastic bands and about a Red Green allotment of duct tape. (Note to physics teachers: budget at least $100/year for duct tape).

It’s the building of real things that brings up real questions. It’s these real questions that make kids want to sit and listen to me teach. I’d be absolutely full of it, if I claimed that kids will naturally derive the equations of motion. (mostly because they only work in deep space…). It’s amazing how much “x-naught this” and “t-squared that” a kid will sit through when they know it’s gong to help them bean a peer with a tennis ball from 100 yards.

The kids really enjoy the dual approach of energy and force here. They can see how the two work together, and they can see how energy really helps when Hooke’s law complicates the acceleration during a test fire. (The acceleration changes as the band relaxes, this math is usually beyond your average high schooler. I make my calculus kids deal with it, though)

What this lesson is also good for is highlighting one of my tacit objectives. Science is a descriptor not a generator. It sure as hockey sticks generates knowledge and understanding, but it doesn’t generate the phenomena themselves. The kinematics equations are the biggest load of garbage taught in the standard physics curriculum, because they’re mostly useless for even the simplest engineering task. The discrepancies between their answers and the siege weapon’s behavior is a fantastic talking point.

The day finally comes. We divvy up the shoe boxes into teams and they get building. 500 shoe boxes gets you some impressive structures. I wish I had pictures. When I revisit this post next year, I promise to take pictures. We take turns firing at each other. Many teachers at this point would make the kids stop and do math before shooting each time. I thought that would be cool, but it’s not. Working the math into the design process is so much more useful, and I honestly just want them to reap the enjoyment of shoebox-castle mayhem.


  1. You cannot move your feet when the other team is firing at you.
  2. If you get hit with a tennis ball, you’re out until the next game.
  3. You can choose to repair your castle (10 shoe boxes) or fire your weapon.
  4. A team loses when all of their players are dead, or their castle is more than 70% destroyed.
  5. Hand-to-hand combat is not allowed.

It’s really fun to referee this game. Does playing it really help teach the math of physics? Probably not. The game is the carrot. You’ve gained a shared experience for these kids, and you can go back to the whiteboard with some kids who have some genuine questions as to why physics predicted the range of the trebuchet to be 200 yards when they only got 50 out of it. Awesome.

(Oh, make sure you recycle the shoe boxes)