Strong as the Weakest Link
A rocket launching tower — an example of a structure that must withstand immense tension and compression forces.Copyright http://topex-www.jpl.nasa.gov/gallery/spacecraft/gifs/launch-tower-vandenberg.jpg, 2003
To introduce the two types of stress that materials undergo — compression and tension — students examine compressive and tensile forces and learn about bridges and skyscrapers. In the associated activity, they construct their own building structure using marshmallows and spaghetti to see which structure can hold the most weight. In an associated literacy activity, students explore the psychological concepts of stress and stress management, and complete a writing activity.
Engineers consider tension and compression forces when designing a building or structure for our everyday safety, comfort and convenience. Human-made structures include homes, skyscrapers, subways, bridges, tunnels and dams, as well as products such as pens, bungee jumping rope, washing machines, wheelchairs, moon rovers, prosthetic legs or bookshelves, to name a few. Engineers use complex mathematical models to predict the expected loads on these structures and products. They determine suitable material components to support the anticipated forces.
After this lesson, students should be able to:
- Recognize that compression and tension forces are important considerations in building structures.
- Relate that the design of the building will determine the weight the building can withstand.
- Explain how certain materials are good at resisting tensile forces while others are good at resisting compressive forces.
- Realize that buildings fail when engineers do not use designs and materials that are strong enough to resist compressive and tensile forces.