Suspension bridges look light, airy and symmetrical, but suspension bridges traverse great distances and are expensive to build. Since they hang from long, sturdy cables anchored at each end of the bridge, suspension bridges provide math and science problems for all age students. Middle school and high school students can analyse, express, organise and display mathematical and scientific thought through suspension bridge projects.

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## Elementary School Shapes, Relative Concepts, Social Studies

Kindergarten and first-grade students can find shapes and learn relative concepts of proportion. Young students can examine the angles, triangles and symmetry of the bridge. Bridges have collapsed due to poor design and weather conditions. In 1940, the Tacoma Narrows Bridge was the third longest suspension bridge in the world. Four months after the bridge opened, the bridge collapsed in 42 mile-per-hour winds. Scientists think vibrations caused the bridge to fall. The bridge began to sway. When the swaying reached a certain level, the bridge collapsed. In an exercise by Design Technology, basic shapes are presented for the students to strengthen with supporting beams, and solutions are presented.

## Elementary School Mathematics and Science

The cables that suspend a bridge are draped over tall towers. The towers enable the cables to span long distances. The anchors of the bridge are solid rock or massive concrete blocks. The cables evenly distribute the weight of the bridge and carry the weight to the anchors. Elementary and middle school students can calculate the height, width and length of sections of the bridge, and learn how the cables distribute the weight of the cars and bridge.

## Middle School Proportions and Scale

Students can calculated the length of sections of the bridge, cables and the carrying capacity of the bridge. The proportion of the height and weight of the anchors to the length of the bridge, and the proportions of the length of the cables to the height of the towers may be calculated. Have students calculate the measures of angles, identify corresponding angles and measures of sides of the angles. Assign students the task of calculating measurements of a model bridge using scale factors and the measurements of the actual bridge. Students can research the construction of a nearby bridge and how it benefits the state and local area. Interested students can research government and local planning and learn basic economics and budgeting.

## High School Mathematics and Physics

Calculating forces that act on bridges makes an interesting science, math or physics class. As a group project, small groups or pairs discuss or calculate individual forces. For example examine compression, tension, the weight of the bridge and the traffic it carries, the tension on the cables, work done by the cables, bending, the effects on opposite sides of the bridge, sliding, shear, torsion, twisting and the effects of the wind. Returning to the group, each pair or small group explain its findings or calculations to the class. For extra credit, research the tensile strength of the cables suspending the bridge and explain how multiple cables bound together increase flexibility and strength.

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#### References

#### Resources

- Public Broadcasting Service: Forces of Wind and Traffic on Suspension Bridge
- Public Broadcasting Service: Bridges Connecting People and Places
- Public Broadcasting Service: Math and Science Support
- Public Broadcasting Service: Wonders of the World Golden Gate Bridge
- Public Broadcasting Service: Forces on Bridges
- Shodor: Interactive Lessons
- Shodor: Interactivate - Tessellations