Bridge Design Strength Test: Truss vs Beam

Popsicle sticks (100 per design) Wood glue String Small bucket Sand (for weight) Kitchen scale Clamps 2 stacks of books (supports)

1. Build a simple beam bridge using 20 popsicle sticks glued flat, spanning 30cm between book supports. 2. Build a Warren truss bridge using 40 popsicle sticks in triangular pattern, same 30cm span. 3. Allow 24 hours for glue to fully cure. 4. Hang a bucket from the center of each bridge using string. 5. Gradually add sand to the bucket in 50g increments. 6. Record the weight at first visible deflection and at failure. 7. Photograph failure mode.

Beam bridge showed first deflection at 200g and failed catastrophically at 450g. The failure was a clean snap at center. Truss bridge showed first deflection at 800g and failed gradually starting at 1,850g. Truss failure began at one joint and propagated — the bridge sagged but didn't snap completely. Truss used 2x the materials but held 4.1x the weight.

The triangular distribution of force in the truss design is clearly superior. Students consistently find this investigation engaging. Consider having them calculate weight-to-material efficiency ratios. Could extend to test Pratt truss vs Warren truss.