Bridging the Gap William Harris | Malik Jefferson

Why do we build?

Bridges are structures designed to support a load crossing a ravine, river, gorge or other obstruction. In class we used our bridge of balsa wood and hot glue to study the science behind building bridges and the distribution of force.

Characteristics of design

The bridge following testing

Materials: Balsa Wood, Hot glue, Manila folder

Length: 36.2cm | Height: 17.8cm | Width: 9.7cm| Mass: 143.7g| Truss Angle: 55 degrees

Free Body Diagrams

Free body diagram

Fy= 137.2 kg m/s. |. Fx= (137.2)/2= 68.6kgm/s | Fd= (68.6)*(cos 55)= 39.34kgm/s


Strength to Mass Ratio= (0.1437kg) / 14kg= 0.0102kg


The strength to mass ratio of a bridge is a calculation of the mass of the bridge relative to the load it is capable of bearing. Our bridge in particular has a mass of 0.1437kg, however it is capable of bearing a load of 14 kg. Which shows that the bridge is capable of bearing 0.0102kg per unit.

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