We have an opportunity this year to participate in our first homeschool science fair. The kiddos have been fascinated with bridges for a long time so I knew immediately what project we’d undertake … Toothpick Bridges. I’ll share with you my toothpick bridges lesson plan with you here.
Capture Their Attention
Before we began construction, we read again the delightful picture book Bridges Are to Cross by Philemon Sturges. We then used the internet to make observations of many modern bridge designs, particularly those we were familiar with here in Oregon as well as those we’d seen first hand in San Francisco. I set up a little demonstration to show what structure was strongest … squares or triangles … using just drinking straws taped together at the corners to form a square and a triangle.
Strength in Design
I then gave the kids graph paper with which I instructed them how to begin designing bridges of their own. They came up with several designs each – some of which weren’t feasible for toothpicks. They then selected a design that would most easily be reproduced with toothpicks and we proceeded with construction.
Building Bridges with Toothpicks and Glue
In the classroom setting, I used to provide each team with a predetermined amount of money with which they would need to purchase their material … lumber (toothpicks) and welding material (school glue). However, here at home, their imagination and thereby their design were the only limitations.
Testing Bridge Strength
We tested the strength of the bridges by suspending a gallon-sized milk jug beneath the bridge with a pencil. Initially, we had used a smaller container but it turned out to be too small to contain the weights. We then began to slowly add weights (marbles & metal washers) to the container. When we ran out of weights, I began to slowly pour water into the jug.
We continued in this way until the bridges finally collapsed or gave in to the pressure. In the classroom, the eminent collapse and destruction of the bridges was always a highlight and was met with cheers and shouts of enthusiasm. Here at home, I hadn’t anticipated the the big tears that we experienced.
In the end, the two bridge far surpassed our expectations. Buddy’s design took on 16 pounds before it finally succumbed to the weight. Sweetie’s design held more than 19 pounds! Had she had more trusses along the roadway that supported the pencil, we hypothesis that her bridge could have supported more weight as her bridge remained intact with the exception of the road that gave way.
The kiddos are looking forward to presenting their experiment on Friday at the science fair. Buddy is even talking about building more toothpick bridges – but he says he doesn’t want to test them. “I don’t want to break my bridge.”
For more details and links to do this project with your kids, check out my Engineering Marvels: Bridges unit study.