Paper Bridge Challenge | Science of Strong Shapes

Materials

For this activity, you will need:

• 2 sheets of paper
• 2 books, boxes or other supports of equal height
• Small objects to use as weights, such as coins or blocks
• A ruler
• A notepad and pen to record results

How to build a paper bridge

Step 1: Create a simple bridge

1. Place two books or supports a short distance apart.
2. Lay a sheet of paper flat across the gap to create a bridge.
3. Carefully place small weights in the centre of the bridge.
4. Observe how much weight the flat sheet can support before it bends.

Step 2: Change the shape of the paper

1. Remove the weights from the bridge.
2. Fold the paper into a series of triangular or accordion-shaped folds.
3. Place the folded paper back across the gap between the supports.
4. Make sure the folds run along the length of the bridge.

Step 3: Test the bridge again

1. Add the same weights to the centre of the bridge.
2. Observe how much weight the folded bridge can support.
3. Continue adding weights until the bridge collapses or bends significantly.
4. Record your results.

Step 4: Compare your designs

1. Compare the flat bridge with the folded bridge.
2. Which design supported the most weight?
3. Which design bent the least?

How does it work?

Engineers use shapes to make structures stronger and more efficient.

A flat sheet of paper bends easily because the forces acting on it are concentrated through a thin surface. When the paper is folded, its shape changes and it becomes more resistant to bending.

Triangles are particularly important because:

• They distribute forces evenly through their sides.
• They are difficult to deform without changing the length of one of their edges.
• They help structures stay rigid and stable.

Many bridges, towers and roof structures contain repeating triangular shapes because they provide strength while using relatively little material.

This same principle is used in bridge trusses, cranes, bicycle frames and many other engineered structures.

Science fair project: Take it further

Once you have built your paper bridge, investigate how different shapes affect its strength.

• Compare a flat sheet of paper with folded triangular shapes, curved shapes like rolled tubes and rectangular folds. Which design supports the most weight?
• Test different bridge lengths by moving the supports further apart. How does span length affect strength?
• Compare one sheet of paper with two or three sheets layered together. How does increasing the amount of material affect performance?
• Investigate how the size of the folds affects strength. Do smaller folds perform differently from larger folds?
• Create a table to record your results. Which bridge design supported the most weight? Which used the least amount of material for the greatest strength?