In this lesson for grades 6-12, students experience the forces of tension and compression by manipulating objects that are strong in each but not in both. Students then take what they have learned and apply it to the construction of a simple model of a beam bridge and the more complex suspension bridge and inverted triangle support structure. During the lesson, students watch video segments that illustrate the design and construction process in the real world.

Objectives

• Learn the differences between the forces of tension and compression.
• Identify which members in a structure are in tension and which are in compression.
• Apply knowledge of tension and compression to the construction of structurally sound models.

Grade Levels: 6-8, 9-12
Suggested Time: Three class periods

Suspension Bridge at Clifton, courtesy of the Gutenberg Project

Multimedia Resources

Clifton Suspension Bridge QuickTime Video
Citigroup Skyscraper Design Problem QuickTime Video

Materials

Rooftops still collage Flash Image

Per pair of students:

• 1 small piece of string (approximately 10 inches long)
• 15 straight plastic soda straws, each approximately 7 3/4 inches long
• 5 wood or bamboo skewers that will fit easily inside the soda straws
• 20 no. 1 paper clips
• 3 feet of 3/4 inch masking tape
• 2 1-square-foot pieces of flat corrugated cardboard
• 10 feet of non-stretch string or heavy thread
• pair of scissors
• ruler
• film canister
• 15 metal washers or coins
• 1 copy of each of the following diagrams:
  ?
  Constructing a Compression Member (PDF),
  Constructing a Beam Bridge (PDF),
  Attaching Compression Members and Tension Members (PDF),
  Clifton Suspension Bridge Model (PDF),
  Inverted Triangle (PDF),
  Constructing an Inverted Triangle (PDF),
  Citigroup Support Unit (PDF), and the
  Rooftops handout (PDF).

Before the Lesson

Make copies of the diagrams for each team. Do not hand out the Constructing an Inverted Triangle diagram unless students are having trouble determining which part should be which type of member.
Practice building a compression member (see instructions below), so that you can assist teams as they build one for the first time. Save your compression member as a model.

Helpful Hints:

To cut skewers, use scissors to score the skewer while turning it. Then bend to break it at the score. Straighten paper clips by unfolding them sideways rather than twisting them. It may be necessary to slightly spread apart the small loop end of the paper clip to make it fit snugly in the straw. Small pieces of masking tape strategically placed work better than larger, random applications of tape. The section of tape closest to the joint does most of the holding. Long pieces are not necessarily stronger. Use “load buckets” to test models quantitatively. To make a load bucket, carefully push the end of a paper clip through a plastic film canister near the rim, and then bend it to form a hook. Fill the canister with metal washers, coins, or other objects of uniform size and weight. Hang the canister from the part of the model to be tested.

The Lesson

Part I: Testing Tension and Compression

1. Hold a piece of string or thread by grasping one end in each hand, and ask each student to do the same. Demonstrate that the string offers little resistance when you try to bring your hands (and the ends of the string) together. Then show that the string strongly resists your attempts to pull your hands (and the ends) apart. Explain that the resistant force they feel when pulling the string taut is called tension. Tell them that in the following activities they will use strings whenever the instructions call for a tension member.

2. Hand out copies of the diagram Constructing a Compression Member (PDF) and ask teams of two to follow the instructions as they construct their own compression member. (Adjust lengths as necessary if your straws are not 7 3/4 inches long.)

When students have finished constructing their compression members, hold up your model and demonstrate its characteristics. Show students that, in contrast to the tension member, the compression member strongly resists your efforts to push your hands together, yet simply comes apart when you pull on the ends. Explain that the resistance force they feel when pushing on the ends is called compression. Tell students that for this lesson, all compression members must be constructed this way. (For longer beams, they can lengthen the straw and skewer sections; for shorter beams, they should use two of the three straw sections and one skewer section.)

3. Hand out copies of the diagram Constructing a Beam Bridge (PDF) and ask teams to follow the instructions to build their own beam bridge. This bridge should be constructed using 1/2-by-1-inch cardboard rectangles. When students are finished constructing the bridge, have one team member hold it upright with the bridge’s ends supported by books. Have the other team member test the bridge’s strength and stiffness by pressing down lightly in the center. Alternatively, have students test their bridge with a load bucket (see Helpful Hints). After testing, have teams construct two additional beam bridges with the larger-size cardboard rectangles and test them, too.

4. After all three beam bridges have been tested, have teams record their observations. Lead a discussion about construction successes and failures and what affect the size of the cardboard rectangles had on beam strength and stiffness.

Part II: Clifton Suspension Bridge

5. Show students the Clifton Suspension Bridge video.

6. Hand out copies of the diagrams of the Clifton Suspension Bridge Model (PDF) and Attaching Compression Members and Tension Members (PDF). Working in pairs, have students study the drawings and sketch a construction plan before they begin building. Their plan should clearly identify tension and compression members. Explain to students that for the purposes of this activity, the two crosspieces between the towers are non-load-bearing and can each be made of a single piece of soda straw. Also suggest that they use a piece of cardboard for their bridge’s roadbed. Have students construct their model, carefully following their sketch and construction plan.

7. When construction is complete, have students test their bridge quantitatively using a load bucket. Ask them to compare their original sketch to their working finished model and record their conclusions about what worked and what had to be changed.

8. Have students watch the Clifton Suspension Bridge video again and discuss any new observations they might have. Point out that the real Clifton Suspension Bridge has cables that descend from the tops of the towers to the cliff faces on both sides of the gorge.

Ask students:

• What parts of your bridge work in the same way?
• How is your bridge different from the real bridge?
• How could you make your bridge stronger?

Citigroup Center Photo by Johan Burati

Part III: Citigroup Skyscraper Design Problem

9. Show students the Citigroup Skyscraper Design Problem video and discuss any observations they have.

10. Hand out the Inverted Triangle (PDF) diagram and explain that this shape is the chief structural component of the Citigroup Tower. Based on this diagram, ask students to sketch a construction diagram incorporating compression members of the same dimensions as those constructed in Part I. If students have trouble determining which part should be which type of member, distribute the Constructing an Inverted Triangle (PDF) diagram.

11. Now have students construct an inverted triangle based on their construction diagram. When finished, have students test their construction by pressing down lightly on the ends. After refining their design and recording their conclusions, have students build three additional triangles identical to the first.

12. Hand out the Citigroup Support Unit (PDF) diagram. Have students mount their four inverted triangles on top of a one-square-foot piece of cardboard. When they?re finished, have students test their single supporting units by placing a flat object (like a notebook) on top of the inverted triangles. Have students make any necessary refinements to their design or construction and record their conclusions.

13. For a final test, stack single supporting units one on top of another to replicate the Citigroup Building. (Recommend that students place the most solidly constructed units at the bottom.) Test the skyscraper by stacking notebooks on top.

Check for Understanding

Show students the Rooftops still collage. Describe the climate differences between Catalina Island off the coast of southern California and the Rocky Mountains of Colorado. Point out that a single foot of snow can produce a two-ton snow load on an average-sized house.

Have students write a descriptive essay, including simple diagrams like those in the Rooftops handout (PDF), that explains how a combination of tension and compression members allows pitched roofs to bear the load of heavy snow better than flat roofs. Ask students to predict the most common type of roof in New England and then in Florida, and explain why.

Related Resources to Check Out

Forces Lab Flash Interactive
In this interactive activity, choose one of the actions of squeezing, stretching, bending, sliding, or twisting to explore compression, tension, shear, and torsion.
Arch Bridge QuickTime Video
This video describes the forces and design features that give arches their strength.
Train Truss Animation QuickTime Video
This animated sequence provides a close-up look at how a truss-stiffened bridge manages tension and compression when a train passes over it.

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Learning Science in Informal Environments draws together disparate literatures, synthesizes the state of knowledge, and articulates a common framework for the next generation of research on learning science in informal environments across a life span. Contributors include recognized experts in a range of disciplines–research and evaluation, exhibit designers, program developers, and educators. They also have experience in a range of settings–museums, after-school programs, science and technology centers, media enterprises, aquariums, zoos, state parks, and botanical gardens.

Learning Science in Informal Environments is an invaluable guide for program and exhibit designers, evaluators, staff of science-rich informal learning institutions and community-based organizations, scientists interested in educational outreach, federal science agency education staff, and K-12 science educators. To read the book in PDF form, click here.

Javier Movellan, Terrence J. Sejnowski,  University of California at San Diego

Abstract

Human learning is distinguished by the range and complexity of skills that can be learned and the degree of abstraction that can be achieved compared with those of other species. Homo sapiens is also the only species that has developed formal ways to enhance learning: teachers, schools, and curricula. Human infants have an intense interest in people and their behavior and possess powerful implicit learning mechanisms that are affected by social interaction. Neuroscientists are beginning to understand the brain mechanisms underlying learning and how shared brain systems for perception and action support social learning. Machine learning algorithms are being developed that allow robots and computers to learn autonomously. New insights from many different fields are converging to create a new science of learning that may transform educational practices.

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Early childhood mathematics is vitally important for young children’s present and future educational success. Research has demonstrated that virtually all young children have the capability to learn and become competent in mathematics. Furthermore, young children enjoy their early informal experiences with mathematics. Unfortunately, many children’s potential in mathematics is not fully realized, especially those children who are economically disadvantaged. This is due, in part, to a lack of opportunities to learn mathematics in early childhood settings or through everyday experiences in the home and in their communities. Improvements in early childhood mathematics education can provide young children with the foundation for school success.
Relying on a comprehensive review of the research, Mathematics Learning in Early Childhood lays out the critical areas that should be the focus of young children’s early mathematics education, explores the extent to which they are currently being incorporated in early childhood settings, and identifies the changes needed to improve the quality of mathematics experiences for young children. This book serves as a call to action to improve the state of early childhood mathematics. It will be especially useful for policy makers and practitioners-those who work directly with children and their families in shaping the policies that affect the education of young children. Click here to download a free copy of the full report.

This survey released by the Organization for Economic Cooperation and Developing provides the first internationally comparative perspective on the conditions of teaching and learning, based on data from over 70,000 teachers and school principals who represent lower secondary teachers in the 23 participating countries. Click here to read the results.

The study, Teaching middle-school engineering: An investigation of teachers’ subject matter and pedagogical content knowledge, found that past experience influenced how teachers used the curriculum. The teachers with more years of teaching experience made more connections between mathematics and science concepts and the engineering unit and tended to use a more student-centered teaching approach than those teachers with fewer years of teaching experience. The study also revealed that the teachers’ non-educational engineering experiences were important factors that contributed to their engineering knowledge. For example, one teacher who had worked as an appliance repairman demonstrated strong knowledge of engineering and science concepts such as friction, gears, work, torque, and redesign that he attributed to his prior work experiences. The study also showed that the science teachers demonstrated stronger knowledge of the engineering design process.

SEAN BROPHY, Purdue University; STACY KLEIN, Vanderbilt University; MERREDITH PORTSMORE, Tufts University; CHRIS ROGERS, Tufts University

ABSTRACT
Engineering as a profession faces the challenge of making the
use of technology ubiquitous and transparent in society while at
the same time raising young learners’ interest and understanding
of how technology works. Educational efforts in science,
technology, engineering, and mathematics (i.e., STEM disciplines)
continue to grow in pre-kindergarten through 12th
grade (P-12) as part of addressing this challenge. This article
explores how engineering education can support acquisition of a
wide range of knowledge and skills associated with comprehending
and using STEM knowledge to accomplish real world
problem solving through design, troubleshooting, and analysis
activities. We present several promising instructional models for
teaching engineering in P-12 classrooms as examples of how
engineering can be integrated into the curriculum. While the
introduction of engineering education into P-12 classrooms
presents a number of opportunities for STEM learning, it also
raises issues regarding teacher knowledge and professional
development, and institutional challenges such as curricular
standards and high-stakes assessments. These issues are considered
briefly with respect to providing direction for future
research and development on engineering in P-12.

(Journal of Engineering Education)

http://soa.asee.org/paper/jee/paper-view.cfm?pdf=996.pdf

A special video report from the National Science Foundation addresses classroom dynamics, math fluency and the use of technology to foster math learning. http://www.nsf.gov/news/special_reports/math/index.jsp