Grace’s Folded Bridge

Grace’s toy traveller needs to cross a blue paper river. She lays a flat sheet between two wooden blocks. When she adds a small wooden cube, the middle sags. “We need stronger paper,” she says. Ms Woods wonders whether the shape could change instead.

They find two matching sheets and keep the blocks the same distance apart. Grace checks that both ends have firm support. Ms Woods places a tray beneath the model so fallen cubes will stay on the table. They are testing a model, not a bridge for people.

Grace makes a fold, then bends the sheet backwards and forwards into an accordion shape. It is still the same kind of paper. The folds create ridges across the gap. She sets it on the supports without adding glue, extra sheets or blocks under the middle.

They add matching cubes one at a time near the centre. The folded bridge holds more before bending. Grace counts carefully and keeps her fingers clear of the small load. “The paper changed shape,” she says. “It did not change into a different material.”

They compare the flat and folded versions again. The gap, cube size and way of placing the load stay similar. Ms Woods explains that shape can affect how a structure carries a load. One successful design does not mean paper can carry anything.

Grace sketches the ridges and both end supports. She includes the version that sagged. It helped her see the problem. Next time she could compare different folds, changing one feature at a time rather than changing everything and losing track.

The tiny traveller crosses safely during their game. Grace uses only the small load they tested. Her bridge is useful for this pretend river. She would never stand on it or expect a much larger bridge to work simply because this one did.

In a book, they find real bridges with different shapes. Engineers choose materials, supports and designs carefully. Grace points to her drawing. “My first bridge taught me where to begin.” A bend in the paper became the start of a better plan.