Beam, truss, arch, suspension… Bridges vary in their design, their length and how they balance two main forces, tension and compression. Tension is a pulling or stretching force which acts outward and compression is a pushing or squeezing force, acting inward.
The goal is that there is no overall force to cause motion and do damage. A bridge will buckle if compression, the force pushing down on it, becomes too much; it will snap if tension, the force pulling on it, overwhelms.
Depending on the purpose of the bridge, how much weight it will need to hold, and the distance it needs to cover, engineers can figure out which bridge is the best bridge.
STEP 1: Place several books about 6 inches apart.
STEP 2: Fold the papers into different paper bridge designs.
STEP 3: Place the paper across the books like a bridge.
STEP 4: Test how strong your bridge is by adding pennies onto the bridge until it collapses.
STEP 5: Keep a record of how many pennies your bridge could hold before it collapsed! Which paper bridge design was the strongest?