## Materials

• 20 straight (not flexible) drinking straws
• Small paper cup
• Scissors
• Tape
• 2 chairs
• Measuring stick or tape
• Pennies or other weighted objects

## Instructions

Introduction

Engineers often use a truss design in bridges, steel buildings, roofs, and even on the International Space Station. A truss looks like a series of connected triangles. Triangles can resist distortion due to their shape unless the beams they’re made of break—this makes trusses incredibly strong and stable. Trusses resist forces in all directions. Forces include compression, tension, torsion, and shear.

Want to learn more about the forces that act on trusses? Watch this NASA video!

Did you know that the International Space Station, where astronauts live and work, is a series of cylindrical modules, connected by 11 truss segments? Known as the Integrated Truss Structure, they act as the backbone of the International Space Station.

While you can’t design and test your own truss structure in space, you can down here on Earth in the form of a bridge.

We challenge you to design a straw truss bridge that spans more than 25 centimeters and holds as much weight as possible without collapsing.

There are 3 constraints for this challenge (an engineering constraint is a limitation on your design):

• Use only the materials listed, but you don’t have to use all of them.
• The span of the bridge has to be longer than 25 centimeters, so that it will sit on the edges of the two chairs.
• The bridge has to hold the weight of pennies or other objects without collapsing.

Brainstorm

• What does a truss design look like? There may be a truss bridge near you, or a building where you can see the trusses holding up the roof inside. Find pictures of truss structures and notice their similarities and differences.
• Draw some truss designs for your bridge that you think will make it really strong.

Build and Test

• Place two chairs exactly 25 centimeters apart. Your bridge will span the distance between the chairs.
• Construct your straw-and-tape truss bridge. Place it so the ends rest equally on the two chairs.
• To test your design, place pennies in the paper cup and rest it on the middle of the bridge. Keep adding pennies. How many can the bridge hold before it breaks?

Evaluate and Redesign

• Where was the weak point in your truss design? See if you can strengthen that part and make your bridge hold even more weight. Engineers pay attention to design flaws so they can redesign and eliminate them.

Make Changes and Try Again!

Now, challenge yourself further by designing an Integrated Truss Structure like those used on the International Space Station. Build a second truss bridge between the chairs, and then connect the two bridges with a third truss structure between them. How much weight can your connecting truss hold?

Share Your Results with a Teacher, Parent/Guardian, or DiscoverE!
You can email photos to DiscoverE at social@DiscoverE.org