Are You a Good Steward? Bridge Building with Spaghetti

Last year, we made the switch the CMP3 math curriculum, which focuses way more on high-level thinking and applications of math concepts to real world problems. Our first unit of the 7th grade year focuses on two-dimensional geometry. We build, we measure, we analyze.

We really realize how much of our world is dependent on polygons. They're everywhere. We like them aesthetically, and they can be used really effectively. Consider for example, the tesselating hexagon shape that honeybees use in their hives.

I think it's so cool that God created them like that. They're such great stewards of their resources thanks to hexagons. This, along with hexagonal thinking, has really made me fall in love with hexagons over the past couple of years. It's by far my favorite shape. 

In the course of our study, we also learned about how strong triangles are in the building process. When you look at bridges, you see them everywhere. We learned more from Chris Woodcock, a bridge architect: 

We discussed all of the factors that a bridge building team needs to consider. Materials. Design. Weight load. Length of the bridge. Budget. Weather. 

Then we talked about stewardship: How might we responsibly plan to use resources to build a strongest bridge while responsibly using (or not using) the resources we have? 


I handed out this packet and had students form groups of three to four, and they got busy planning their bridge building. The bridge with the best weight of bridge to weight of load would win. They knew their resources would be spaghetti and hot glue, but they had to remember a few things: 

  • Hot glue weighs a lot more than spaghetti.
  • Any scraps created would count towards the weight of their bridge. I gave them a cup to collect them in as they built. Some students weight the extras separate. Some used them to reinforce their bridges. 
  • Use the power of triangles.

I loved watching them build and listening to their conversations about polygons and stewardship.  (Not to mention they started cheering when they realized that we had an 80-minute block of math instead of the standard 40-minute period.)

Then we began the weighing process. I took a red solo cup, punched some holes in it, looped a string from the cup to their bridge, and we started adding weights. However... we didn't have enough weights to break them. Oops. My students bridges were too strong. 

We ended up having to reconvene at a lunch period to try again, this time with ice cream buckets which we filled with water. Even then, our system wasn't great. I need to get a bigger bucket for next year so that we don't need to add a second bucket. 

We were all a bit surprised by how strong triangles of spaghetti and hot glue really were. The lighter bridges were actually stronger in our class. 

We had a lot of fun and truly realized the power of polygons! Here are a few of the things my students wrote in the reflection process: 

  • "We used mostly triangles because they are the strongest polygons in building architectural designs."
  • "I learned that it takes a lot more work to build something, even something this small. I can’t imagine how much work it would take to build an actual bridge!"
  • "We chose that our bridge was a little longer than others because if it bent it would have a higher chance of falling."
  • "We chose to do the smallest sizes we could that would fit the requirements to save resources and minimize waste."
  • "Sometimes things fail and you have to try again."
  • "I would use more glue on the bottom of the bridge instead of focusing on the sides, and I would have accounted for where the weights were hung from."

So many wins there. I look forward to doing the 2.0 version of this project next year. I think next year I'm also going to give them a budget and make them buy their materials. I'll make hot glue cost a bit more so they have to use it more sparingly.