For heavy car and railroad traffic, beam bridges are replaced by truss bridges. A truss bridge is a bridge that bears its weight through its truss system. A truss bridge is a type of bridge that carries its weight through its truss system. This truss system is composed of triangles and rectangles that give its strength.

Truss bridges are one of the oldest types of modern bridges and are more economical to build than solid beam bridges.

### Teacher Notes

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## Step 1: Gather Your Supplies

Supplies:

- A bag of marshmallows, foam cubes, or cheese balls
- A box of toothpicks
- Tape (maybe)
- Small cups
- Paper clips
- Weights – pennies, paper clips, etc. Anything is OK as long as they weigh the same. You want to compare how much different bridge designs can support

## Step 2: Create Your Squares

- Create a square with four marshmallow pieces and toothpicks. Create 3 more. Put them together to create a cube.

## Step 3: Connect the Cubes

- Create several more cubes and put them together until you reach 10 inches in length. Remember, your bridge must be longer than the span it needs to bridge (add an inch or two to the total length of your bridge).

## Step 4: Create a Bridge

- Place the bridge between two desks, tables, chairs, etc.

## Step 5: Test Your Bridge

- Hang a small cup in the middle of the bridge (use hole puncher and paper clips if you can't find these wedding favor cups) and load it with pennies, paper clips, etc. to weigh it down and test its strength.
- Hang more cups if the bridge is strong enough to support it.
- Add more cups until the bridge breaks.

## Step 6: Failure and Improvements

What I built here is a truss bridge based on squares and cubes, but you should try to build a truss bridge with triangles. Of course, the elementary school students (especially primary students) struggle with the fact that hypotenuse is longer than the sides (problem with toothpicks' lengths), but it adds to the complexity of the project. I encourage that in my intermediate classes.

Fail Spectacularly (our Science project motto) and have fun!

## 3 Discussions

Question 2 months ago on Step 1

Where do you get the foam cubes? Marshmallows are not working too will and I don't even want to try cheeseballs.

Reply 2 months ago

The foam cubes from Amazon are expensive. If you get lucky, you can find them from Dollar Tree. Like 50 foam cubes for $1. You can't beat that! However, it's quite difficult to get them consistently.

Answer 2 months ago

There are a lot of great foam cube options on Amazon! Looks like it's a popular teacher resource :)