An easy balsa bridge project for school
A simple first bridge project for a class or a home: materials, a basic truss to copy, how to test it, and what to record. No special tools needed.
Updated · 1 min read
Short answer: build a simple Warren truss from 1/8 in balsa sticks across a 30 cm gap, load it with a bucket of sand, and record how much it held and what broke first.
Materials
- 1/8 in square balsa sticks (about 10 for a first bridge, plus spares)
- White wood glue
- A hobby knife or craft cutter, a sanding block, a ruler, pins, a board and wax paper
- A bucket, string and sand or small weights, and a kitchen scale
- Safety glasses
Steps
- Draw the plan full size: two long chords 30 cm or a little more, and diagonals zigzagging between them to make triangles. See truss basics.
- Cut the sticks to length, with a sharp blade and light passes, and sand the ends. See cutting joints.
- Build two identical trusses flat on the plan, pinning sticks in place and gluing with small amounts. See gluing joints.
- Join them with a few cross-pieces, keeping them square.
- Weigh the bridge.
- Test it across two supports, loading a bucket slowly, with glasses on. See testing safely.
- Record the load, the first break and the efficiency. See efficiency.
Questions to ask students
Which sticks were pushed and which pulled? Where did it fail? What would you change? Then rebuild with one change. See the lesson plan.