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Toothpick Bridges

toothpick-bridges

Bridge Engineering

My kiddos have been fascinated by bridges for a long time. Every 5-6 weeks we travel to the Oregon Coast, crossing numerous bridges. The most memorable one is the McCullough Memorial Bridge that spans Coos Bay. A recent trip to San Francisco really brought bridge design and construction to life (the Bay Bridge was under construction). Upon our return home, we read numerous books about bridges and the kids were asking lots of questions. When an opportunity to participate in a homeschool science fair presented itself, we knew immediately what project we wanted to undertake.

Join us - as we walk through the steps of designing and ultimately testing the strength of our toothpick bridges.

Bridges Are to Cross

Planning & Design

Before we began construction, we read 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. 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 Toothpick Bridges

Read About Bridges

What Materials Do I Need?

In addition to the materials listed here, you will also need graph paper to design your bridge and a plastic jug or bucket in which to add weights (we used a gallon sized milk carton).

  • Toothpicks
  • School glue
  • Wax paper
  • Graph Paper
  • Cardboard
  • Plastic bucket
  • String

The Great Bridge Builder

toothpick-bridges

Construction

In the classroom setting, I used to provide each team with a predetermined amount of money ($1,550,000) with which they would need to purchase their material ... land (cardboard - $500,000), lumber (toothpicks - $10,000 per piece), cable (string - $500 per cm), welding material (school glu - $850 per day's supply), building-plans paper (4 sheets graph paper; wax paper - $40,000), fines ($1,000 - $10,000), vandalism ($50,000). They were required to keep a balance sheet and to write checks to make purchases. This added a fun element to the project and enabled the teams to come up with company names as well as to assign specific tasks to members (i.e. the student who was good at math was the accountant, etc.). However, here at home since my kiddos are young and not yet skilled at math with such large numbers, their imagination and thereby their design were the only limitations. [ Checks and balance sheets are available in the Pollard book, "Building Toothpick Bridges" but you could certainly create your own. ]

To begin, a piece of wax paper is laid atop the design and taped down. Toothpicks are then laid down upon the paper and glue is applied to the intersecting toothpicks. Upon completion of the first side, it is left to dry overnight. The wax paper is then removed from the design paper and this process is repeated for the second side. When both sides are dry, the completed sides should be able to be removed from the wax paper easily.

The two sides are then brought together upright on the land (35cm x 15cm piece of cardboard). To do this, a tiny hole is poked into the cardboard where each of the eight toothpicks can be inserted. Cross-connecting toothpicks are then laid across and glue is added to adhere the two sides together. The river measures 15cm across (essentially a 15cm square in the center of the cardboard). Two 5cm squares should be drawn on each side of the river for the footing. The bridge should be built up from these two footing areas and continue across the river.

Upon the roadway, there should be space available for a small toy car to pass without obstruction. A small toy boat can pass freely under the span of the bridge.

Amazon Spotlight

toothpick-bridges

Testing Bridge Strength

To test the strength of the bridges, a pencil is laid across the road way. A plastic bucket or container of some sort is then suspended from the pencil. Weights (marbles, metal washers, etc.) are added slowly to the bridge. Each new weight must be held for one minute before more weight is added. Continue in this way until the bridge collapses or breaks under the strain of the load.

Scroll to Continue

An AP Physics Class Design Competition

Presenting at the Science Fair

Will post results & pictures soon.

Have you designed and tested toothpick bridges? Do you have questions on how to implement this project in your classroom? Take a moment to leave a comment and/or ask questions!

Feedback Wanted

Shannon from Florida on June 13, 2012:

Great lens! I'm featuring it on my lens on bridges. https://discover.hubpages.com/education/lesson-pla

Eva Varga (author) from Oregon on October 14, 2010:

@dannystaple: I'd love to see this lens! :)

dannystaple on October 13, 2010:

Oh yes - this will be awesome - I think it will be in a collection of lenses I am going to build on cool stuff to build with my kid when she's older.

Eva Varga (author) from Oregon on June 02, 2010:

@Pebblekeeper: I added the cost of the materials so that you could have an idea of how to set that part up. This part of the project was a huge learning opportunity for older kids ... forcing them to budget their money and not be wasteful. In a classroom setting it also helped to assure they worked together as a team. Enjoy!

Pebblekeeper on June 01, 2010:

I am so glad you put in the instructions for this great project - And, since I have Middle School Boys, I do think we might go ahead and plan/design/save/budget and then purchase "supplies". A little autocad going to far?

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