Sticky Bridges

I've been reading about doing this STEM activity for a while now, and during the last week of school was the time to try it! The idea is that students build a bridge created with no more than 100 toothpicks and 50 mini-marshmallows. The students had 25 minutes to create the bridge (I did it in pairs.). After the time was up, I planned to test the strength of the bridges by suspending them on a pair of stacked books with a space of six inches between them. I told students that I planned to put metal washers (in a bowl) on top of each bridge until it collapsed. The winners would get Smarties candies or Dum Dum lollipops. So much excitement in the classroom! 

First, I gave students about 5 minutes to plan and design their bridges. Some used mini-white boards, others used their iPads, and others simply discussed it with their partner. Then it was off to work!

I loved hearing the students talking to each other about why they thought their design was best. Here are some of their creations I witnessed. As I walked around, I asked students to explain their logic. Some couldn't put it into words, while others explained exactly why they thought that their design would support weight.

Looks pretty, but not so strong.

This one is a little more intricate.

Popular pattern, no? 

This one won! It supported 13 washers.

Finally, it was time to test the bridges. The one directly above won because, as the creators explained, "It had crosses and plus-signs to make it stronger." In addition, it has two layers.

"X" is where the magic lies.

Here, one of the designers explains his creation to me. Notice the "X" he is making with his hands!

When I have more time, (and I will make more time for this next year) I would like students to make a second bridge the next day based on the what they learned from their first go-around. Should be interesting. In addition, it could also be extended by studying bridge designs AFTER this lesson. I purposely didn't do this because I didn't want students to have prior knowledge of this. Clearly, most students have seen bridges before, but have they ever really looked at the engineering? I'll bet they will next opportunity they have!