You need: up to 10 sheets of printer paper, up to 1 m of masking tape, scissors (with a grown-up's help), a ruler, two equal stacks of books, a paper cup with a string or paper-clip hanger, dried beans or rice, a kitchen scale, and safety glasses (or sunglasses).
- Define and brainstorm: sketch three different ideas (for example, a truss of rolled tubes, a deck folded like an accordion, an arch under the deck).
- Plan: choose one. Draw it with measurements. Predict how much it will hold.
- Build your prototype. Weigh it on the kitchen scale and record its mass in grams.
- Test: set the books 30 cm apart. Place the bridge across. Hang or set the cup at the middle. Add beans a spoonful at a time, gently, until the bridge fails (collapses, tears, or sags so the cup touches the table). Weigh the cup and beans it held just before failing (the total from the last spoonful it held). Wear eye protection; keep your face away from the bridge as it nears failure.
- Evaluate: calculate efficiency = load held ÷ bridge mass. Note where and how it failed.
- Improve: change one thing and build and test again. Do at least 2 versions.
- Communicate: make a short report or video with your sketches, data table, efficiency for each version, and what you learned. Clean up spilled beans right away, as they are slippery on the floor.
What to look for: a design that meets the criteria and constraints, a data table (mass, load, efficiency, how it failed) for each version, one change at a time between versions, and explanations that use unit words: compression, tension, buckle, triangle, symmetry, point of application. Many well-built paper bridges hold well over 20 times their own mass, but any honest result is fine: the improvement between versions is what matters.