Session 3A: Compression and Tension Models
A Teacher-Colleague Review Activity
Overview
In Session 3B you will be asked to engage, discuss and evaluate an interactive computer model that demonstrates the structural forces that act on bridges. To prepare for this model, let’s review the forces of tension and compression.
Tension and compression are important structural words. All structures – whether a tent, skyscraper or bridge – exist at all times in either tension or compression. A balance (or equilibrium) of these opposing forces is what makes a building stand up. Unbalanced forces signify instability, and severely unbalanced forces can lead to a building or bridge collapse.
Materials
- Plastic Flexible Straws
- Optional: Rubber bands, a new bar of soap
Procedure
- Starting with a kinesthetic approach, stand face-to-face with a teacher-colleague partner. Extend your arms with palms facing your partner. Now touch palms with each other and gently apply force. Try (carefully), while keeping your arms extended, to move your feet back while supporting each other. The resistance force you feel when pushing against each other is called compression.
- In what position did you and your partner feel the most “stable”? What are some examples of how compression is used to support a structure?
- Now, again facing each other, firmly grab hands or wrists and (carefully) apply a force by leaning back. Try (carefully) moving your feet toward each other. The resistance force you feel when pulling on each other is call tension.
- In what position did you and your partner feel the most “stable”? What are some examples of how tension is used to support a structure?
- Optional: Stretching a rubber band is an effective model to demonstrate tension, while squeezing a bar of soap models compression.
- Compression and tension working against each other can be demonstrated by using a flexible straw. Lay the straw on the table and observe what happens to the flexible, “accordion” portion of the straw as you move the ends of the straw toward you.
- Which side of the straw is under tension and which is under compression? How can you tell? Take a moment to draw the deformed “accordion” portion of the straw and label the compression and tension areas.
- With a partner, look at the photos below and observe the structures. Where do these structures use compression, tension, or both? Make rough sketches and label the areas of compression and tension in each structure.
Discussion
- What are the advantages of having students physically experience science vocabulary as you did with compression and tension? What are the possible disadvantages of a kinesthetic student activity?
- Which of the activities that you have just experienced do you think best represent compression and tension? If you teach about forces, which ones might you use with your students? Why do you think your choice would work best?
- How do the kinesthetic and flex-straw activities you did meet the definition of a “model”?
- How has your understanding of developing and using models in your teaching changed, if at all, so far?
Take Two minutes for a quick evaluation of today’s session: Module 2 Session 3A Survey
Facilitator Note
For the next session, remind teachers to bring their laptops.