# House of Cards

#### Kris Rosfjord,Yolanda Zhang andMonique deBarruel

Materials: deck of playing cards, candy

Directions:

1. Arrange the cards so that they form a structure without altering the cards in any way by bending or folding.
• Can your structure hold a piece of candy?
• How many?
2. Now try folding the cards to assist in building the structure.
• Does folding allow you to make a wider variety of structures?
• Does this make the structure sturdier? (Will it hold more or less candy?)
3. Now you are allowed to tear cards to assist you in making your structure.
• How does this affect the stability of your structure?

Challenge:
Using the different methods above (leaning, bending, tearing) build a structure out of cards that can:

1. be as tall as possible and able to hold a piece of candy.
2. hold the greatest weight. You can have all the candy your structure can hold!
3. withstand wind. Think of how you can maximize the stability of the house in all directions.

The “Science” of Card Houses

Every building is subjected to forces. Most forces acting on buildings are caused by:
• Gravity acting on the building and its contents. The force (load) is mass times the acceleration of gravity (g=9.81 m/s^2). This mass includes the weight of the materials to make the building!
• Wind acting on a surface. (The moving air is being decelerated.)
• Earthquake (The movement of the ground is trying to accelerate the building.)

Forces acting on the building need to be resisted by internal forces in the structure. To distribute the forces with playing cards a basic truss (series of triangles) is made. Triangles are extremely strong and distribute forces well. The joints of the triangles are vital to the stability of the structure. Bending and tearing the playing cards allows you to make stronger joints.

Wind can provide a torque (force that is not axial to the beam) on your building. To resist this, members of the truss that are perpendicular to the two other members of the triangle are added. Without this axial force, these additional members carry no load.

Compare the structures you created with the structure of an aqueduct. These ancient structures used arches rather than triangles to distribute the forces of the load. The Roman aqueduct below stretches 2950 feet long through Sierra de Guadarrama. It is made of rough-hewn massive granite blocks, joined without mortar or clamps.