Leo laid a sheet of paper between two piles of books. He placed a toy car in the middle. The paper sagged, and the car slid onto the table.
“It needs more paper,” he said, reaching for the packet.
His sister May held out one hand. “Try changing the shape first.” She folded a fresh sheet backwards and forwards, making a row of narrow pleats. Leo balanced the folded sheet across the same gap. This time, the car stayed in place.
Leo added a second car. The bridge bent a little, but it did not fall. He sketched the folds in his notebook and wrote down how many cars it held.
“Now we can compare them fairly,” May said. “Keep the gap the same when you try another shape.”
Leo moved one pile of books closer, then stopped. He put it back where it had been. He wanted to find out whether the folds made a difference, rather than whether a shorter bridge was easier to support.