The Paper Bridge Challenge
Teams have 10 index cards, 30 cm of tape, and 20 minutes to build a bridge that spans a 20 cm gap between two desks. A cup is hung from the middle, and weights are added until the bridge fails. Team A lays one card flat and it holds 40 g. Team B folds cards into accordion pleats and holds 300 g. Team C rolls cards into tight tubes and holds 650 g. Team D's bridge holds 900 g, but the team used an extra 45 cm of tape borrowed from another team. The class must decide which design feature mattered most and whether Team D's result should count.
1. Which design feature mattered most among Teams A, B, and C? Use the data to support your answer.
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Shape mattered most. All three teams had the same cards and the same 30 cm tape limit, so the main difference was how the cards were shaped. A flat card held only 40 g because it bends easily. Folding the card into pleats made it stiffer and raised the result to 300 g. Rolling the cards into tubes made them even stiffer and held 650 g. Because the materials were kept the same, the increase from 40 g to 650 g can be attributed to the change in shape. Team D cannot be compared fairly because it used extra tape.
2. Should Team D's 900 g result count as the winner? Explain your reasoning.
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Team D's result should not count as a fair win unless the team rebuilds using only 30 cm of tape. The challenge set a material limit, and Team D used 45 cm more than allowed. Extra tape could have strengthened joints or wrapped the cards, so the 900 g might not come from the design idea alone. To make a fair comparison, every team must use the same materials and the same amount. The class could let Team D test again with exactly 30 cm of tape, then compare that result with the other teams.
3. The class wants to build an even stronger bridge in a second round. Describe a plan that would produce trustworthy evidence about which design is best.
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Keep the rules identical for every team: 10 cards, 30 cm of tape, a 20 cm span, and the same cup and weights. Change only one design feature at a time, for example comparing tubes made with different numbers of cards or comparing pleats with tubes. Test each bridge the same way, adding weight in the same increments, and record the mass at failure. Repeat each design at least twice because one test can be misleading. Then compare the averages. If a design holds more weight consistently under the same rules, the class has evidence that its shape makes it stronger.