How to make it
7 steps. Tap one when it's done.
All projectsTwo bridges, one shoebox of cardboard
Cardboard Blue Water Bridge
Build two different bridge shapes over a blue cardboard river.
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Time40 minplus glue drying
You get1 model bridge
DifficultyMediumSome mess
SectionCrafting
What a grown-up does
Cutting the thick cardboard.
Why that works
Triangles can't change shape without breaking a side, so a bridge made of triangles stays stiff. An arch works differently: it squeezes its load down into the ground at both ends. Both hold up, which is why the real bridge could use one of each.
Lambton County twist
One real bridge span uses strong triangle shapes while the other has a curved arch.