I walked the interchange site this morning and felt fine until I tried to get back into the car. My hips had tightened up enough that getting one leg under the steering wheel required a second attempt. That seems backward after a morning spent moving, but I had also driven an hour each way and sat through the briefing. At home I found the stretching sheet from physical therapy, folded under a warranty in the kitchen drawer. I remembered the first exercise immediately and not the last three. Jen suggested putting it somewhere I might actually see it. Reasonable suggestion, although my first response was to explain why the drawer made sense.

My son asked one of the other robotics parents for help while I was standing right there. I was glad he knew who to ask, in principle. In practice I felt sidelined and spent the next few minutes finding a reason to check their work, which they had under control. I had missed the last meeting for the interchange project, so of course they already had a plan. There was nothing unfair about it. He was excited to show me the finished mechanism afterward and I almost spoiled that by pointing out a possible improvement. I stopped myself, but it bothers me that I needed to. I'd been looking forward to being useful more than to seeing what he had done.

My son asked whether a bridge knows how much weight is on it. I explained that structures don't know things, then spent ten minutes using words like responds and carries, which probably did not help my case. He wasn't asking for a load calculation. He wanted to know why something that looks still can be doing so much. I've been turning that question over because it's a better starting point than the explanation I gave. At his age I built a popsicle-stick bridge and mostly wanted it to hold more books than anybody else's. I can remember the moment it failed very clearly. I don't remember once wondering what it was doing before that.