Design, build and test model bridges as you determine how shapes affect the strength of structures.
What You'll Need
20 non-bendy, plastic drinking straws
Small paper cup
200 to 300 pennies (or washers or weights)
Two tables or two chairs for a testing station
Optional: Balance for weighing
What to Do
Explore bridge design by creating a bridge that must cross a local "river." The bridge must span 25 cm across a gap between two tables or two chairs. The bridge cannot be attached to the support structures in any way, so you may want to make it slightly longer than 25 cm.
You can use only 20 straws and as much clear tape as you need. You can cut your straws to any length, but you cannot have more than 20.
The bridge must support as much weight as possible. To measure the load, the bridge must securely hold a small cup. You will test the load by placing as many pennies in the cup as possible and counting how many it can hold.
The bridge cannot disturb the river's fish population, so it cannot bend down more than 4 cm as pennies are being placed in the cup. Measure this bend by holding a meter stick vertically next to the bridge.
Think critically about your bridge design before building it, and consider sketching a blueprint first. You'll have 20 to 30 minutes to build the bridge. When you're finished, predict how many pennies you think your bridge will hold.
There are many types of bridges: beam, truss, arch, suspension and cable-stayed. A truss bridge uses trusses, or a series of triangles, for support. Triangles are structurally the strongest shape because they allow weight to be evenly spread throughout a structure, which allows it to support heavy loads.