Last summer I had an inspiring curricular brainstorm. Since I teach high school physics, I am always looking for engaging and authentic projects for my students. I was at a primitive skills school open house when I saw a hand-made cider press making cider for all of us. I was intrigued at the possibility of building cider presses with my students as a vehicle for teaching simple machines and Newton’s 3rd Law. I drew up some supporting documents, bought material I thought we would use, and pitched it to the kids. They loved the idea. We could even sell these presses when we were done to raise money for a charity of the kids’ choosing! Oh, this was going to be big!
If that’s what had actually panned out, it would make for an inspiring story, I suppose, but this is not that kind of story. It started out all right. The kids researched design ideas. The three groups in this class spent time finalizing their design plans. We went down to the woodshop to begin construction. I interspersed instruction on simple machines with labs regarding Newton’s 3rd law, and then back to the woodshop for more construction. This was taking significantly longer than I had planned, but that’s how these projects almost always go. It was becoming clear that the different groups had different levels
of woodshop readiness and motivation. Then came the kicker. The plans we found online called for 1” thick diameter acme threaded rod to crush the apples. When I was ordering these online, such a stainless steel rod would cost over $100, so I opted for something thinner, 3/8”. How much different could that be?
My key mistake in this whole scenario was that I did not build a cider press myself that summer when I had the idea. I would have learned that if you try to crush apples with a 3/8” steel rod, the rod bends
beyond all repair. I would have learned that you can’t weld stainless steel. I would have learned that even when you do succeed in applying a significant amount of pressure via the rod, you must have a frame that can withstand an equal and opposite force.
Here’s where the learning got interesting. I should have recognized the flaw in the design right away, but I didn’t see that when you screw the rod down to crush the apples that force must push the frame upwards. We found ourselves standing on the frame to try to keep it down to crush the apples, but instead as we cranked down, it lifted the frame and us off the ground instead of crushing the apples!
In the end the cider presses were ostensibly a failure, but what a vivid example of Newton’s 3rd law! There was definitely an “aha!” moment when the kids realized what was happening and connected it with what they had learned in class. I’ll be honest, I had that moment as
well, so next year when we do this unit again, I’ll be ready.