Drilled holes in the frame for the pivot arm.


Drilled holes for the angled base.


I trimmed up the lever arm on the bandsaw. I won't let him anywhere near the router, so I also knocked the edges off with a roundover bit. Then back to him for glue and clamps.




Two wiped on coats of Danish oil for the win.





We originally used 4 rubber bands, which ended up launching the ping pong balls something like 20 feet. I down-powered it so we could run the experiments at a reasonable scale in the garage.


We used video to determine the horizontal distance and elapsed time. In the context of his algebra-less experiment, that was enough to prove which launch angle sent the ball the furthest. I showed him how to use the kinematic equations to resolve vertical displacement and the component vectors of velocity, but I wouldn't say he was highly interested in that. But we had fun making the catapult and shooting ping pong balls all over the place. And when Mom wasn't looking, we launched cherry tomatoes all over the kitchen as well.

I am proud of the fact that his project represents both his actual levels of understanding and effort, and I look forward to seeing it between the projects of the kids who home-sequenced the genome of their dog and the one who built a functional model of the Jarvik heart.