Objective: To understand tension and compression
1) Students will find the definition of tension and compression.
2) Students will describe how tension and compression occurs.
3) Students will demonstrate tension and compression.
The Internet can be used to get illustrations of each.
Note to teacher: The Euclidean and Non-Euclidean Geometry with The Geometer's Sketchpad would be very useful for turning this activity into a computer activity.
Each Student should be able to define tension and compression and show an
Illustration. Extra credit should be given to students who construct a demonstration
This activity may be used in conjunction with this lesson6
Have students build a people bridge to experiment with the forces of compression (a pushing, squeezing force), tension (a pulling force and torsion (a rotational twisting force). Have pairs of students face each other with palms touching and feet 0.5 m (1.5 ft) apart.
Have students slowly move their feet back while keeping their palms touching until the bridge feels balanced and they cannot move back any further without falling down. Where on the bridge do students feel forces of compression and tension? Have one person move two steps to the left.
What happens to the balance of the bridge? How does torsion affect the stability of the bridge? What forces might cause the support structure of a real bridge to rotate?
Students should be allowed to discuss these questions in small groups and come to a consensus on the answers. One person designated as the recorder, should write up the report for submission to the teacher.
Students who have decided to build a suspension bridge for their project, may be interested in demonstrating this activity to the class.
What are the anchorages for?6
Tie two loops of string around the tops of two hard cover books of similar size. Tie a third string to each loop so that it hangs loosely between the books. Press down on the center string. What happens?
Next, stand the two books about 10 inches apart. Put a stack of heavy books on one end of string to secure it to the table. Then pass the string over each book (letting some string hang loosely between the books). Place a second stack of books on the other end of the string. Press again on the center string.
What happens? Notice how the anchorages (stacks of books) help to stabilize the bridge.
This activity could be used at any time to generate or maintain student interest in the unit.
What happens when a load pushes down on a beam bridge?
Take a flat eraser or a small sponge and slice a shallow notch across the top and bottom. Create a beam bridge by supporting each end of the eraser (or sponge) with a stack of books. Press down on the center of the bridge.
What happens to the top and bottom notches? Notice how the top notch squeezes together in compression while the bottom notch spreads apart under tension.
In addition to the applications included in the unit, there are many more applications that can be adapted to teach skills. Ratio and proportion can be used to compare different types of bridges. Students can practice Scale drawing by drawing a sketch of a bridge using a scale. Students can practice estimating length and height by using a scale drawing.
Measurement and measurement conversion can be taught by requiring students to measure in one unit of measure and convert to the other unit. Students could be required to explain the operation (add, subtract, multiply or divide) required to go from a smaller unit to a larger unit and vise versa.
Since my class are inclusion classes (special and regular education) all of my students will not be read to go to Euclidean and Non-Euclidean Geometry with the Geometer's Sketchpad, I would suggest that teachers start their computer exercises with Math Blaster Geometry. This is a fun and non-threatening way to introduce students to geometry.