I wanted to teach parabolas (quadratics) differently in my precalculus classroom. I have always hated just doing it algebraically, since students never see how parabolas are actually used in the world. I have always wanted to use rockets as a way to model a quadratic function, but I didn’t know how to avoid wind and air resistance. That made me think about catapults, but 3D printing catapults for an entire class would take a while.
After receiving the glowforge and thinking for a while, I landed on rubberband powered catapult that fires M&Ms.
I modeled it up in Fusion360 and found the immensly useful Shaper Origin plugin to export the SVGs. Then I was able to nest it using deepnest.io so everything fit perfectly on 1/4 of a sheet. Because of this, the file attached has minimal waste so you can create enough for a classroom on a budget. I cut prototypes on proofgrade and then used the less expensive HomeDepot 1/4 ply for the final. The settings for were 5.3mm thick at 150 speed and full power for the cuts, 300 speed and 10 power for the score.
The catapult is fun to use and reliable for data collection. I glued everything up with superglue and CA Accelerator. I built 5 in total and could build one in 15 minutes by the end. The pivoting arm is a 1/4 aluminum dowel, but a wooden dowel would work as well. I would suggest using hardwood, like red oak, to avoid deflection over time. You can use any rubberbands you want, really, but I used two 64 sized. There are different slots for various release angles, unfortunately I didn’t make one for 45 degrees but you can adapt it. The letters written on the parts just help identify which pieces to keep once it comes off the bed.
Details for teachers:
If you are a teacher and want to use this in your classroom: here is the rough worksheet I created to help guide students along. I also created a function generating spreadsheet to create functions based on the data students collected. This helped me quickly check if students were correct when they finished. I’m not claiming that everything is absolutely correct, I think it is, but these resources helped guide my students along when they were creating their functions. I used the following videos to help me plan (I didn’t create these):
- video 1 - deriving function for height given time
- video 2 - using h(t) to find the vertex form of h(d)
All in all the students enjoyed the project. I didn’t have them build it because of time, but they would have enjoyed that too. They struggled a bit with the two different functions, but by the end they were able to use their functions to shoot the M&M’s into buckets at different heights off the ground. If you’re planning on using skittles, be warned, they don’t fit into the launcher.