Lesson 1: Introducing vertical compression

Title: Creating structures to withstand vertical compression

Author: A. Stillman

Subject: Structural Engineering

Grade: 6

Week:

Unit/Lesson Plan #: 1

Unit theme(s): Green building, vertical structures, social responsibility.

Textbook references: n/a

Learning objectives:

* Compression, tension, and torsion are all factors that affect a vertical structure.

* Crushing is the compression of a material beyond it's strength.

* Buckling is the bending and collapse of a column under a compressive load.

Key Questions, Concepts, or Themes:

* What allows for this building to stand up? (show this picture)

* What factors determine the strength of a column?

- cross-sectional diameter

- shape

* Which cross-sectional shape of column do you think is the strongest? (square, circle, triangle)

Stage 1: Show the picture above with prompt for discussion. Emphasize the giant mass that is supported by what is essentially a hollow structure. How is this possible? Students typically arrive at two basic ideas: the need for a foundation, and the use of vertical and horizontal beams

Stage 2:

Tell students that today's focus is on vertical beams. Ask students to imagine they were a steel beam inside the building..."What forces would you feel?" Diagram the situation, showing where the horizontal beams attach...I used the word "squishing" force to describe the situation in kid-friendly language. I then asked if anyone knew a formal term for this kind of force. We then defined Compression as a "squishing" force. I then elicited the opposite word, grabbing one the students' raised hands and dragging him in his chair while asking, "what kind of force is his arm experiencing right now...it's not a squishing force, but a stretching force. Define tension as a "stretching." For both of these forces, I explained that they act along a line.

We then looked at an index card. Compressing the index card between my hand, I asked students to rate how well the card withstands vertical compression. I then randomly distributed four cards to students and asked those students to change the shape of the card in such a way that it would better withstand vertical compression.

Illustrate and define buckling at this stage. Buckling: the failure of a compressed object due to bending.

I then used the four shapes to illustrate different possibilities. For a simple fold, or set of folds, I asked students if any of them could think of a connection to corrugated cardboard. Sketch a cross-sectional view of corrugated cardboard to illustrate. Students may also show square, triangular, and circular column structures. Have several on hand in case they do not come up with this on their own.

Stage 3: Now introduce the challenge. Task students to build a structure from 6 index card that holds the greatest number of math workbooks. Provide scissors and index cards only. No tape or glue. You may want to give students a hint about notching the paper together...or not. Set a timer for the activity and

This part of the lesson was extremely chaotic, but fun. Students began testing their structures at different times, stacking and counting the number of math workbooks they could get their structures to hold. One group was able to get as many as 130 books to stand on their structure!

Closing the activity is pretty tough given then amount of excitement it generates and the fact that many groups will still want to keep testing and refining their designs.

The two synthetic points to draw out of discussion are:

1) Cylindrical columns tend to best resist buckling.

2) A larger distance between columns tends to imporve stability.

Homework: No homework in this class.

Assessments: (attach/link copies)

__ Group assessment

__ Observation of process/student work

__ Self-assessment by student

__ Teacher generated assignment

__ Written project

__ Test/Quiz

__ Other: ____________________________________