Building Toothpick Bridges .. a Lesson Plan

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.Buddy's Design

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.

toothpick bridge

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

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.

toothpick bridge collapse

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.

toothpick bridge

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.

toothpick bridge

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.”

Engineering Marvels: Bridges

For more details and links to do this project with your kids, check out my Engineering Marvels: Bridges unit study.

About Eva Varga

Eva is passionate about education. She has extensive experience in both formal and informal settings. She presently homeschools her two young children, teaches professional development courses through the Heritage Institute, and writes a middle level secular science curriculum called Science Logic. In addition to her work in education, she is an athlete, competing in Masters swimming events and marathons. In her spare time she enjoys reading, traveling, learning new languages, and above all spending time with her family. ♥

10 comments on “Building Toothpick Bridges .. a Lesson Plan

  1. Wow! That looks like an amazing experiment! I have a laundry basked full of Popsicle stick/tongue depressor buildings and marble runs in the garage. Would you consider doing an ebook or squidoo page for how to assemble the bridge? School Glue? How long does it take to dry? I’d love to see a page on squidoo after the science fair! Way to go Kiddos! (and Jon would be BAH-HA-Hawling if his bridge broke! even if he knew it was coming. :)

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