## Introduction: Bridge Project

Welcome to my end of the year Bridge Project for 8th grade science students. I use this project at the end of the year to put a few of the concepts we have learned about over the course of the school year into practice. It is also extremely useful for kids who are starting to fall off in terms of motivation that are day-dreaming about summer. This provides my students with an opportunity to go hands on and engage in an engineering practice that becomes tangible by the end of the project. I use this project to satisfy NGSS Standards MS-ETS1-1 through MS-ETS1-4. These are all of the engineering standards used for 8th grade science in Iowa.

## Supplies

I get all of my materials for this project from Hobby Lobby. I use the slim sticks as the base pieces and the mini sticks as the supporting portions of the bridge. Each group also gets a 1.25oz bottle of Elmer's Glue. At my front table under my supervision, students use razor blades to cut the pieces of wood. When groups have successfully completed all of my requirements for building, they get a Ziploc bag with 60 mini sticks and 2 base pieces as well as their glue bottle. The bag and glued bottle are numbered so they can find it quickly.

## Step 1:

I start this project after two months of learning about basic physics concepts. To get my students into the spirit of things we start by taking a little time to play cargo bridge. This is a free game offered online on sites like Cool Math Games. Here is a link: https://www.coolmathgames.com/0-cargo-bridge

## Step 2: Let's Use Bridge Designer 2016

So now that the students are in the bridge building spirit it's time to introduce Bridge Designer 2016. I start by giving a basic tutorial of how to use the software. After this I give them the class period to get familiar with using the Bridge Designer. At this point I don't give them any design constraints. I also don't show them any examples of previous bridges or allow them to sit with their partner. This allows them to have some of their own creative freedom before they get into a group.

## Step 3: Design Constraints

And welcome to the reality check. In the real world their are budgets of time, money, and patience. Attached is my Evaluation of Design document in which students will be scoring each design based on each of these ideas. In summary, it is now the job of the groups to create four different bridge designs on the design software that utilize no more than 60 of the craft sticks to build.

## Step 4: Evaluate Your Designs

After groups have finished designing four different bridges on the design app, it is time for them to evaluate each bridge based on a rubric of four categories. We talk about how not every category should be considered the same, and that each group should come up with their own hierarchy for which categories are the most important.

## Step 5: Choose a Design to Build

Once the groups have evaluated their designs, they need to pick a bridge to move forward with. After they pick a bridge, they answer the questions shown in the image.

## Step 6: Make Blue Prints

When making the blueprints, I have my students stretch the image left and right that is on their collection document until it is the width of one of the base pieces. They then stretch the image up and down until the length of what they consider a full piece on their bridge matches. Once the image is the right size, they trace it onto graph paper. When they are finished they should have a blueprint of each side and their plan for where they will put their pieces on the bottom of the bridge. This is mostly done for budgeting the sticks, but also to make sure the bridge can be tested.

## Step 7: Quality Control of Materials

When each group receives their materials I tell them it is up to them to inspect the quality of each piece and trade out any pieces they deem unworthy. This is the only time I allow them to make changes. They should be looking for any bent, broken, non-full length, or otherwise damaged pieces to remove. Just a supply note. Expect to lose up to 10% of the mini sticks to this process as they will be cracked, broken, or warped. I like to put this responsibility on them as I am already sorting about 3,000 sticks to get all 50 groups ready for bridge production.

## Step 8: Plan, Layout, Measure, and Cut.

After they are good with the materials they have been given, it is time to layout, mark, and cut. I have found it is great to use page protectors on the blueprints from this point forward. Elmer's glue doesn't stick to them, so if they spill it is not a problem and it will keep the blueprints intact to be able to produce two identical sides. The order of building is side, side, bottom, top. Again, we use razorblades in the front of my classroom under my supervision. They give very clean cuts on the craft sticks which allow you to create precise angles. The more precise the angle, the higher wood surface contact area at the joint which creates stronger joints.

## Step 9: GLUE!

Once the pieces are the appropriate length, students put them in place right on top of the page protector. Again, it doesn't stick and what does stick can be easily peeled off when dry. Pro Tip: Use tape to hold pieces down. Especially the base piece which is extremely important. They will continue this process until they have two equal sides.

## Step 10: Finish Sides

Continue cutting and gluing all pieces until you have a completed both sides of the bridge.

## Step 11: Erect the Bridge

It's time to put the bottom and top on. In this step tape is your friend. I like to tape the base pieces to the page protector to hold them in place. I use 2x4 scrap blocks and tape to plumb the sides of the bridge during the glue up process. From here it's pretty simple to glue in the bottom pieces. After that it's on to the top and just like that, you have a bridge that is ready to test.

## Step 12: Let's Test the Bridge

So today is the fateful day to destroy all of your student's hard work. They'll actually enjoy it. I use a bucket of some sort and fill it with sand one scoop at a time. When the bridge breaks, we put the bucket on a scale to measure how much weight it was able to hold before failing. I built a bridge testing board to test the bridges by taking a three foot long section of 3/4" pine board and cutting a 6" x 6" square out of the middle of it. I found it was hard for students to see what was going on with the bridge under stress though, so we added two 2x4 pieces to each side to raise the platform for easier viewing.

Participated in the
After School Challenge