Kids & Play

#70 · Engineering bridge challenge

Build a bridge using only chopsticks and elastic bands, then test how much weight it holds before it dramatically collapses.

Give a group of children a pile of chopsticks, some string and a glue gun, and ask them to span a 30cm gap between two chairs and hold a book. It is the classic STEM activity, and the materials cost nothing.

How to do it

1. Set two chairs 30cm apart and declare the gap between them unbridgeable by any other means.
2. Hand out equal piles of chopsticks, string and glue, and set a time limit.
3. Build.
4. Test by adding books one at a time until each bridge fails.
5. Discuss where each one broke, which is the actual lesson.

Why it works

Chopsticks are strong along their length in both tension and compression and weak across it, so a bridge built from flat laid sticks bends and fails almost immediately while one built from triangles does not. A triangle cannot change shape without changing the length of a side, which is why every real truss bridge is made of them.

Tips & warnings

• Don't give them the triangle hint straight away. Let one bridge sag first - it lands far better.
• Set a chopstick budget to force real design decisions.
• Wooden clothes pegs make excellent joints and clamps while glue sets.

Common questions

What age does this work for?

Roughly seven upwards for the building, with an adult on the glue gun. Younger children get more out of stacking and balancing than out of the design brief.