2nd – 4th grades
Difficulty of Project
Less than $5.00
Approximate Time Required to Complete the Project
One to two hours to experiment with the construction of the bridge; one day to prepare the science fair display
To create a bridge between two chairs using books
- 2 matching chairs
- 20 hardback books (approximately 8 ½ x 11-inches)
- Measuring tape
All bridges have a center of gravity. The center of gravity helps the bridge to be balanced and stable. The center of gravity is easy to locate when an object is symmetrical.
In this investigation, the center of gravity is explored.
center of gravity: the average location of weight of an object
span: the distance between the two ends of a bridge
compression: a force that works to shorten or reduce in length
tension: a force that works to lengthen
The center of gravity aids in the stability of a bridge.
- How can you build a bridge between two chairs with books?
- How does the center of gravity help balance and support a bridge?
- What other factors are important in building a bridge?
- Gather the necessary materials.
- Set the chairs facing each other about one foot apart.
- Place one book on each seat so that the spine hangs over about one inch. Continue placing books on top of each other staggering them each about one inch until the books meet in the center.
- Experiment with how far apart you can put the chairs and still create a bridge with the books. Record the results.
- Experiment with how few books you can use to make a bridge connect the chairs when they are one foot apart. Record the results.
“How Bridges Work” by Michael Morrissey at www.howstuffworks.com
“Geometry of Bridge Construction” at http://www.faculty.fairfield.edu/jmac/rs/bridges.htm
“Bridge Technology” at http://ww.fhwa.dot.gov/bridge
“Building Big Bridges” at PBS.org