And speaking of medieval siege engines...

Today is the day for Middle Girl's big demonstration of the scientific principles behind the paper trebuchet we built.

The bigger problem than construction was how to get the thing to school in without tearing it up. "You're going to have to be REALLY careful, because it's made out of what?"

"Paper, Dad."

"RIGHT! Paper."

The way it's made, it is possible to disassemble it into three pieces, the throwing arm, the weight basket, and the frame. But, disassembly must necessarily lead to undisassembly if she was going to get any class points for it, and I don't think she has the necessary fine motor skills required to keep from making a large pile of paper. So a carrying case was needed of some sort. It stands about a foot high, and I thought at first I could find an adequately-sized shoebox from the kabillions all around the house.

No such luck.

Next best was a copier paper box, which we also have tons of. (If you are imagining the home of one of those people who you see on the news who hoard every useless thing and live among stacks of papers and magazines and books, well, you're WRONG! We NEED every single useless thing we have!)

Anyway, got a paper box and set it on the kitchen table. Hmmm. Fits in there just fine with the box set up on one end, but it still needs something to keep the terrifyingly effective combat weapon from rolling around (we modified it a bit and put wooden wheels on it) and bashing itself to pieces. The search for an effective set wheel chocks carried me hither and yon throughout the far reaches of the garage. I thought about cutting some strips of foamcore board, but that would have involved cutting. I thought about gluing down some dowels inside the box, but that would involve gluing (and I wasn't really sure the dowels would arrest the motion). What, ho!?

Ah-HAAA! Useless junk, indeed! I spied a cardboard box full of decorative Christmas cookie tins. The lid of one of the Oreo ones looked to be just about the right wheelbase and track. Popped it off, ran back in the kitchen, crossed my fingers, held my breath, lowered the model down, and...perfect!

I popped it back out and put several loops of tape (the cheap guy's double stick tape) on the top of the lid to hold it the box and stuck it back in place. Slick.

Of course, before putting it away for the evening, we had to make a run-through just to see if she could load it and fire it without help and explain all the subtle physics involved.

The ammunition has evolved away from using marbles to something a bit less lethal--Dots candy. (As long as you don't try to eat them, you'll be just fine.) I gave her one and let her load it into the sling, draw back the arm, set the hook, and fire it off. Perfect shot, dead center in the upper cabinet doors.

"Okay, now how does it work, Bec?"

"Um, well, there's a lever and it has a weight and when you pull it down and the weight goes up it make po...potential energy."

"And?"

Blank look.

So I went back over how the potential energy gets all kineticky and what sort of lever it used and how the sling makes the arm even longer and how the wheels help the weight drop down straighter which makes more of the energy go into throwing the Dot.

Somewhat less blank look.

"Aw, you'll do fine."

She ran on off somewhere while I carefully marked a series of big black arrows all around the box.

UP.

(No use taking chances.) Be interesting to see how this all turns out.
posted by Terry at 2:11:00 PM