After a week of heavy rains, he had cabin fever. The day lurched along in a not very productive fashion, and then stopped. Lessons were clearly over. I acquiesced, and we settled in to play with Lego.
Inspired by a picture from an old set of instructions, I built a small catapult and used it to heave Lego blocks at him. Of course he wanted to have a go, and then, of course, he wanted to adjust it to throw the blocks as far as possible. We were shooting yellow or red blocks, these being the easiest to find when they inevitably go under the furniture. It turned into a short lesson on leverage.
The simplest way to shoot further, is just to hit your catapult harder. As we found out, though, there are limits to that, because if you hit it too hard, the whole thing falls apart.
He worked out that you can move the pivot point to get a better throw. Having a relatively long loaded end gets you some good distance, although if the fulcrum moves too close to the force end of the beam, it all becomes a bit unmanageable.
Having decided on the optimal point for the fulcrum, we then played around with its height. If it was too low, we barely got any movement at all. If it was too high, we ran into the engineering limits of our design and the catapult kept breaking every time we tried to shoot it. After a bit of trial and error, we found the most effective fulcrum height for the design we were using, as well as the most comfortable distance along the arm.
Our best throw made it half way across the lounge room, through the door, and to the far wall of the room beyond – a distance of a bit over six metres. He just thought that was terrific.
I drew up some diagrams as we went to describe the physics behind what we were playing with. Partly, this was to elaborate on what we had just learned so he could use it next time this idea came up. Partly it was to justify to myself that we were doing a physics lesson here, and not just throwing Lego blocks around the room. Sometimes you need all the leverage you can get.