Designing a bridge to span a gap and hold weight is so exciting! This is a highly engaging activity and students love it!
We have built so many different types of bridges. Students love to drive little cars across their bridges and they love to add weight to the bridge to see how well it will support it.
Let me share a few kinds of bridges and the mistakes I made in the beginning! Tips for not making those same mistakes will be included! Bottom line—building bridges in STEM Class is FUN!
In this post, for your convenience, you may find Amazon Affiliate links to resources. This means that Amazon will pass on small percentages to me with your purchase of items. This will not create extra costs for you at all! It will help me keep this blog running!
The First Bridge
The first bridge we built was … interesting. My part was to determine the materials we would use and also determine what the bridge would span. I decided each team needed two boxes. The bridge would rest between the boxes – what I call the span or the roadway.
Check the photo below- we taped two tissue boxes about six inches apart.
This is a bridge made from straws, toothpicks, string, and paper clips. They were quite flimsy and only a few groups were successful.
My mistake: Those boxes we used were not the best bridge span. We also had a rule that the ends of the bridge could not be attached to the boxes. They collapsed in the middle easily.
So, before we tried this again I re-thought the span and the materials.
Bridges with Straws
I took toothpicks out of the materials – due to a safety issue (for me). Students (these are 5th graders) will try to pierce the materials with toothpicks and I really don’t want to see them accidentally pierce their fingers!
And, I changed the bridge span device to a plastic bin. These bridges are longer- we built them the length of the bin and we used the string in a very clever way.
Most teams opted to use the string as a form of tie-down which added stability to the span. These held a lot of weight!
Marshmallow Bridges
This is the one we call the marshmallow bridge. The materials are toothpicks and marshmallows. Yes, I know I just said I didn’t like using toothpicks. But here the students are only stabbing a soft marshmallow- not a straw or cardboard box.
What do you think my mistake was with this one? If you think it is using marshmallows as a building material, you are partly correct!
TIP: The real mistake is buying good marshmallows. Buy the store brand and open them the night before you use them. The stiffer the marshmallow the better these bridges work!
You can see in the photo below that the bridge completely collapsed as the students tried to move it . Those really soft marshmallows are hard to work with!
TIP: This marshmallow bridge is fun. Have wet washcloths on hand to help clean up their gooey fingers and your tables!
Index Card Bridges
You cannot get much easier than this one. You just need index cards and something to use for adding weight to the bridge.
My mistake with the rules on this one was something I did not foresee as a rule we needed. The first class that tried this took several cards, rolled them into a tube, and then sat the weight bowl on top of the cylinder. We completely filled the bowl with pennies and that cylinder would not collapse.
This single cylinder held the weight…
…but, is that a bridge?
Well, no. So, we had to back up and talk about what this bridge would resemble. It needs to have a roadway. Several columns can hold the roadway aloft. Ok, the kids got busy and had a new bridge in 2 minutes. They made a long roadway with about 5 rolled card columns and placed the weight bowl on top of one of those columns.
Clever students, right? So we changed the rules again. You do not drive your car only on the columns holding it up. The weight bowl has to be placed on the actual roadway! This (finally) turned out to be very challenging!
Suspension Bridges
I wanted to build a suspension bridge for a long time and had to build one on my own first. I needed to see if this was a task students could tackle.
Here is what I found. Tape will not hold the bridge pieces together. The tension in the string pulls taped pieces apart. White glue will work, but the drying time for white glue is prohibitive in a 45-minute class session.
Can we handle hot glue?
Yes! And I can proudly say I thought of everything with the rules of this one. We had hot glue rules! We also had rules for how to make holes in the cardboard.
I bought low-temperature glue guns and we used wide craft sticks. Students had to mark the spots on cardboard for the holes (the strings went through those holes) and I made the holes with my tools.
TIP: These need a good base to place the bridge on- we used a stiff poster board one year and foam board another year.
Drawbridges
This is another bridge I wanted to try for a long time.
My mistake? I thought students would know what a drawbridge was!
TIP: They did not! Most of my students had never seen a drawbridge, so I found some short videos showing different drawbridges and the ways they open.
Then we tackled building one.
The results were spectacular.
We used the same tables pushed together and sturdy cardboard for the bridge roadway. Students really worked hard attaching strings and materials so the separate sides of the drawbridge would operate.
The most fun of this challenge was SHARING TIME! Students were so proud to show their working drawbridges raise and lower!
The Ultimate Easy Bridge
This bridge is the best invention ever! Straws and tape.
Two rules- it has to span a 12-inch gap and it has to look like a real bridge. (If you think the “real bridge” comment is silly, go back and look at the very first photo. That bridge was a mess.) The gap is across two lab tables that are 12 inches apart. This is an excellent way to create the roadway. The bridge has to be sturdy because the floor is too far away to make support columns!
Here’s what I did for this one- I gave the students a handout that had drawings of real bridges. The teams chose the model they wanted to build and then determined a way to use straws and tape. Just look at that one in the photo! Awesome!!
Alright, folks, I hope you learned a few things not to do when building bridges! Click on any of the images to see them in my store!
RELATED ARTICLES
Picture Books for STEM!
