Critical Load (Student Instruction)

Teams build a house of cards and see how much weight it can support before it collapses. In the process, they consider structural integrity, strong building design, and materials.



  • 12 playing cards
  • Scotch tape
  • A small cardboard platform (the bottom of a milk or juice carton works great, or you can cut down a pizza or cereal box)
  • And something small to use as your weights, like pennies or paper clips


  1. Identify the Problem
    The most critical step of any engineering challenge is to understand the problem you are trying to solve:
    • Using only 12 playing cards, how can you design a flat-topped structure that supports as much weight as possible without collapsing?
    • You will need to think like a civil engineer to figure out the critical load. This is the amount of weight or force that causes a structure to fail or fall apart.
  2. Brainstorm Designs and Build
    • Spend a few minutes trying out different arrangements of cards to get ideas for which design would work best.
    • As you build, see how much tape you need to secure your structure. You can use all 12 cards, but you don’t have to.
  3. Test Your Design
    • It’s time to test the strength, also known as the structural integrity, of your house! Will your house stay up when weight is added?
    • When you are ready, place your cardboard platform on top of your structure and count how many pennies you can add, one at time, until it collapses.
    • Be sure to add weight evenly. If your house falls down after only a few pennies, that’s OK. This is why testing is so important.
    • How many pennies did it take for your structure to fail? Record the total number of pennies as your critical load.
    • Or you can calculate the critical load in grams. A US penny weighs 2.5 grams.
  4. Evaluate and redesign
    • Think about any changes you would like to make using these questions:
      • How much weight did the house support? Could it be designed to support more?
      • Where is your structure failing? How can you strengthen the weak points?
      • Did the height of your card structure affect its ability to support the added weight?
      • What was the shape of your card structure? Is there another shape you can try?
  5. Make Changes and Try Again!
    • Redesign your house and test again.
    • Were you able to increase the critical load?
    • Looking for another challenge? Increase the difficulty by building without tape or by using index cards instead of playing cards.
  6. Share Your Results with a teacher, parent/guardian, or DiscoverE!
    • You can email photos to DiscoverE at or post on Instagram/Twitter using the hashtag #DiscoverEChallenge

Activity courtesy of IEEE All rights reserved.

Supplemental content adapted for Dream Big Activities by the Carnegie Science Center.


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