Popsicle-Stick Bridge Load Challenge

Skill Level: Beginner

Time: ~60 minutes

Engineering Fields: Civil Engineering, Structural Engineering

You'll Build: A small bridge made from popsicle sticks that spans a gap and holds weight placed in the middle

Why This Activity Matters

This challenge helps you see engineering forces in action

• Success and failure are visible

• Structure matters more than materials

• Failure encourages redesign, and thoughtful iteration

Core takeaway

Strength comes from structure not just rigid materials.

Learning Objective

Design and build a bridge using popsicle sticks that can span a gap and support as much weight as possible by applying principles of structure, force, and stability.

Materials Needed

• 80–150 popsicle sticks (craft sticks)

• Wood glue or strong craft glue

• Wax paper or parchment paper

• Ruler and pencil

• Masking tape (temporary holding only)

• 2 sturdy books or boxes (to create a gap)

• Paper cup + string

• Weights(pennies, washers, rice, or sand)

• Optional: binder clips or clothespins

Before You Build

Set up your testing area first.

1. Place two books or boxes on a table with a 20 cm (8 in) gap.

2. Tape wax paper to your work surface so glue doesn’t stick.

3. On paper, lightly mark the two “support lines” showing where the books are and the center point where weight will be applied.

   
   

This setup will stay the same for every test.

Step-by-Step Building Instructions

Step 1: Choose a simple Bridge Design

Before building, decide how your bridge will carry load.

• A truss bridge(recommended) uses triangles and spreads forces efficiently.

• A flat beam (not recommended) is easier to build but usually breaks sooner.

  
  

Why this matters:

Triangles resist bending and keep the structure stable.

Step 2: Build the First Side Truss (flat on the table)

1. Lay one popsicle stick flat as the bottom chord (the bottom edge of your bridge).

2. Place another stick above it as the top chord, parallel to the first.

3. Add diagonal sticks between them to form triangles.

4. Glue every joint carefully.

   
   

Use small amounts of glue and press joints tightly together and wipe excess.

Step 3: Reinforce joints (this is where strength comes from)

Most bridges fail at the joints, not in the middle of the sticks.

1. Cut small stick pieces.

2. Glue these pieces over major joints as reinforcements.

3. Focus on the center, near the ends of the bridge, and on any joint where multiple sticks meet.

   
   

Why this matters:

Stronger joints help forces travel smoothly through the structure.

Step 4: Build the Second Side Truss

1. Build a second truss that matches the first in size and shape.

2. Let both trusses dry until they can be safely lifted without bending.

   
   

Matching trusses keep the bridge balanced.

Step 5: Connect the Trusses (Make It 3D)

1. Stand the two trusses upright, about 5–8 cm (2–3 in) apart.

2. Connect them with popsicle sticks across the top like a ladder.

3. Add connectors across the bottom.

At this point, your bridge transforms from “two walls” into a single structure and should feel rigid, not wobbly.

Step 6: Add Bracing to Prevent Twisting

1. Add diagonal braces across the top in an X pattern.

2. If possible, add diagonal braces along the sides.

Why this matters:

Bracing prevents torsion (Twisting), a common cause of bridge failure.

If your bridge feels “wobbly,” add bracing before testing.

Step 7: Create a Load Point

Choose one method: Your test needs a consistent place to apply weight.

• Glue a small platform at the center of the bridge, or

• Attach a string underneath the center to hang a paper cup

This is where weight will be added during testing.

Step 8: Let the Bridge Dry

Allow glue to dry fully.

• Minimum: 1 hour

• Best results: overnight

  
  

Testing too early can cause false failures.

Step 9: Set Up the Bridge for Testing (the challenge)

1. Place the bridge across the 20 cm (8 in) gap.

2. Make sure both ends rest flat on the supports.

3. Position the cup at the center load point (or hang it from the center point).

Step 10: Test the Load

1. Add weight to the cup slowly.

2. Add the same amount each time (for example, 10 pennies).

3. Pause briefly after each addition and observe the bridge.

   
   

Stop when the bridge breaks or can no longer hold the load.

Step 11: Observe and Record

Write down:

• Maximum weight held

• Where the bridge failed (center? joints? end support?)

• How it bent or twisted before breaking

  
  

This data helps guide redesign.

Step 12: Redesign and Improve

Rebuild using what you learned.

Try one improvement at a time:

• More triangles in the center

• Stronger joint reinforcement

• Wider spacing between trusses (prevents tipping)

• Additional X-bracing to reduce twisting

• Double-layered top/bottom chords

Engineering is iterative:

Build → Test → Learn → Improve

What's Happening Physically?

• The top of the bridge experiences compression

• The bottom experiences tension

• Poorly braced bridges fail by bending or twisting

  
  

Your design controls how forces move.

What students should learn

• Forces travel through paths. Good bridges give forces clean paths to the supports.

• Triangles are stable. Rectangles bend into diamonds unless braced.

• Joints matter most. Bridges often fail at connections, not materials.

• Structure beats material. You didn’t change the sticks — you changed the design.