Hands-on Activity The Strongest Strongholds

Learning Objectives

After this activity students should be able to:

• Explain why towers with a higher strength-to-weight ratio are better.
• Explain the steps of the engineering design process and how following it guides us to make design improvements.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

Common Core State Standards - Math

International Technology and Engineering Educators Association - Technology

State Standards

Materials List

Each group needs:

• 60 plastic straws, or more as needed
• 50 cm masking tape or paper tape, or more as needed
• Engineering Design Process (EDP) Flowchart, one per group
• Competition Rules, one per group
• Competition Criteria and Judging Rubric, one per student

To share with the entire class:

• gram scale or kitchen scale, or more as needed
• meter stick or tape measure
• computers with internet access, to research straw tower designs
• a large stack of magazines or books that are each the same size, to serve as weights
• computer and projector to show the Strongest Strongholds Assessment, a PowerPoint® file

Worksheets and Attachments

Pre-Req Knowledge

Students should have an understanding of ratios or fractions to be able to calculate and compare the strength-to-weight ratio for various structures.

Introduction/Motivation

Who has seen a castle or a stronghold? (Wait for raised hands.) Who has ever seen a bridge? (Wait for hands.) Who lives in a house or apartment? (Wait for hands.) Engineers are often required to design large structures that are strong and capable of remaining in place over long periods of time.

Who can think of a structure that is built to be strong? (Expect students to come up with a range of examples such as skyscrapers, dams, bridges, tunnels, their own houses, the school building, roller coasters, trucks, tables, etc.) That's right; many types of structures are built to be strong in one way or another. Engineers also often design structures to be durable so they can provide us with protection from weather and other natural forces. Why is it important that a living space be strongly built? (Expect students to provide a range of answers such as: to keep people we care about safe, so we have a place to go when in bad weather or during natural disasters, etc.]

Today, we are going to design and build towers. When constructing apartments or towers, engineers must take into consideration that different levels must be able to hold additional weight from the presence of people using the structure and the building materials that make the structure. Today, rather than building towers that reach to the sky, we are going to build towers that are strong, really strong. Typically, engineers design towers that use concrete and steel, which are expensive materials! Because engineers do not want to build a tower only to find out that it is not as strong as required, they often build and test models first. What is a model? (Expect students to have an idea that models are simplified representations of reality, often at smaller than real-life scale.) That's right, using models is a way to look at a constructed design and see what might happen to that design in the real world—without spending a lot of money to build it full-scale. We are going build our model towers using plastic drinking straws and masking tape.

Because engineers are concerned with costs, they also try to reduce the amount of time and resources that it takes to get a job done. Would you want to pay $100 for a tower that you could get built for $50? (Wait for the entire class to respond.)

Engineers also work in groups, so we are going to split up into groups of two. Each group will compete against all the other groups to design and build the strongest tower at the lowest possible cost.

To figure out which tower is the strongest for the cost, we are going to compare the strength-to-weight ratio for each tower. Since you are using only straws and masking tape, the group that uses the fewest straws and least amount of tape to build the strongest tower will be the winning engineering design team!

Procedure

Background

Buildings and other structures must be designed to withstand numerous forces, or loads. Through their college studies, engineers learn about how these forces act on one another. If forces occur on a structure that are greater than what the structure is built to withstand, catastrophic failure can occur, which can lead to structural collapse. These collapses are not only expensive, but may endanger human life.

Five fundamental loads are related to building straw towers: compression, tension, shear, bending and torsion. For more information on these forces or to better improve student understanding, reviewing the Fairly Fundamental Facts about Forces and Structures lesson is recommended. A deep understanding of the fundamental forces that contribute to building failure helps students discover weaknesses in their structures. Students can use more materials and different design approaches to improve these structural weaknesses.

To begin, expect students to have some familiarity with the steps of the engineering design process. The engineering design process is an iterative approach in which engineers (or students, in this case) make improvements on their designs based on knowledge that they gain from brainstorming, research, testing and redesign. The activity guides students through the basic engineering design process, in which they make improvements to their towers based on what they learn as they go.

In this activity, students compete to design and build the strongest possible straw tower that weighs the least, within a given amount of time while being at least 60 cm in height. For students to be effective at creating towers, they need to research tower designs. One informative resource for students is to watch straw tower YouTube videos to see other examples and to learn about tower-building concepts and construction techniques as ways to improve the strength of their towers.

Before the Activity

• Make copies of the, Engineering Design Process (EDP) Flowchart, Competition Rules and Competition Criteria and Judging Rubric.
• Obtain several hundred plastic straws and several rolls of masking tape or paper tape. Straws can often be obtained for free from local restaurants or inexpensively through restaurant supply stores, bulk purchase stores like Sam's Club and Costco or online retailers like Amazon.com.
• (optional) To simplify the distribution of building materials, it helps to assemble in advance packets of 50 straws and 20 cm of tape for each group. Then, as the initial packet supplies are used up, groups can obtain additional building materials.
• One or more gram scales are necessary to weigh the straw towers. Calculating the strength-to-weight ratio can be done by the teacher (or judge), by each student group, or together as a class. Gram scales (kitchen scales) are often available inexpensively at local thrift stores and local and online retailers.

With the Students: Day 1

1. Pass out the three handouts for students to consult throughout the activity.
2. Walk students through the design process flowchart so they understand that they will be going through an iterative process to learn about and improve their designs. This is a process that engineers around the world use as they create solutions to problems. Stress that improvement comes with time, testing, and learning from our mistakes and what others have done successfully.

   

3. Divide the class into groups of two students each.
4. Ask: Identify the need and constraints: Go through the rules and criteria/rubric handouts with students so they understand the activity objectives and constraints, as well as how their towers will be evaluated. The competition constraints inform students that they are building weight-bearing straw towers that are at least 60 cm in height.
5. Research the problem: Have students conduct online research such as investigating tower-building concepts and watching YouTube videos showing different straw tower designs. See the Additional Multimedia Support section for a good suggested video. Have students navigate to find the videos themselves or guide them in this research.
6. Imagine: Develop possible solutions: Knowing the activity objectives and constraints, and having just seen lots of ideas from the videos, give student teams 20 minutes to brainstorm initial tower designs. Remind them to use their imaginations and sketch and write down lots of ideas.
7. Plan: Select a promising solution: After students have researched designs and observed the features and characteristics used for different design approaches, have student groups each draw out their most promising designs, which serves as their initial tower design.
8. Create: Build a prototype: Once a group's plan is done, give them a supply of straws and tape to begin to construct that tower design. End the first day by giving students 30 minutes to build their first tower prototypes.

• Before students begin construction, walk them through basic building etiquette: not taking 100 or more straws and 50 cm or more of tape all at once, and only acquiring more materials when needed. (This is less of a problem if groups are given initial pre-assembled packets of materials.)
• Remind students of the importance of using as few materials as possible to obtain the strongest tower. More materials = more cost and more weight.
• (optional) Suggest students consider splitting their initial tape allocation in half the long way as a way to increase the number of joints that can be reinforced, while saving on material usage (and weight).

With the Students: Day 2

1. Test and evaluate prototype. Give teams 15 minutes to test the strength of their straw towers. Follow the measurement and testing rules and scoring as presented on the rules handout.

• Complete the pre-test check list (the Judging Rubric table) on the criteria/rubric handout.
• Weigh the tower before testing. Record the weight in grams on the criteria/rubric sheet.
• To test, add weight in the form of magazines (or books), one at a time, to the top of the tower, until the tower fails (is unable to hold any more weight/magazines). Record the number of magazines that the tower held before failing.
• Weigh one magazine and record its weight on the criteria/rubric handout.

2. Have students calculate the strength-to-weight ratio of their towers. Do this as a class so that students can learn from their peers' designs, and gain more experience with ratios. Record team strength-to-weight ratios on handouts and on the classroom board for everyone to see.

ratio = (magazine weight) x (number of magazines) / (tower weight)

3. Improve: Redesign as needed. Give students an additional 30 minutes to modify, reconstruct and/or entirely redesign their towers, incorporating what they have learned through observing the testing of all towers.
4. During the remaining time, have students continue to test the towers to see if their new designs yield substantial improvements in the strength-to-weight ratio.
5. At competition end, lead a class discussion during which students examine and analyze which designs worked best and what they learned from the activity. See suggested discussion questions in the Assessment section.
6. Conclude by administering the three-question post-assessment presented in a PowerPoint® file to determine if students understand how forces can be better distributed across a tower structure.

Vocabulary/Definitions

model: (noun) A representation of something to show its construction or appearance, or for imitation, comparison or analysis; often at a smaller scale. (verb) To make something to help learn about something else that cannot be directly observed or experimented upon.

ratio: A proportional relationship between two quantities.

stronghold: A well-fortified place or fortress.

Assessment

Pre-Activity Assessment

Preliminary Tower Design: Have students draw tower designs. Pay specific attention to whether or not they incorporate cross beams and other load-balancing structural elements as a way to gauge their base understanding of tower construction approaches.

Activity Embedded Assessment

Observation of Tower Design Evolution: Expect to see design improvements as students work through tower redesigns. Weight-bearing attributes for each tower are measured during the initial testing period prior to redesign, so that improved scores during the second test period indicate that students have learned how to better engineer strong, weight-bearing designs. For activity measurement and testing, follow the construction and competition rules and scoring approach described in the Competition Rules (or similar).

During the activity, groups work to improve their tower designs to make stronger, lighter towers. This process involves iteration of tower building and learning from others. Look for evidence of their growing comprehension through the use of strategies such as straw bundling and the use of cross beams and other structural reinforcements to improve the load distribution across their towers.

Class Discussion: At competition end, lead a discussion to explore the value of the engineering design process and assess whether students learned from the iterative process. Example questions:

• Which design won? Why? (It held strong under the heaviest load for the amount of straws and tape it used. It best met the design constraints. It had the best strength-to-weight ratio. It was a smart design.)
• Which other designs worked well? What aspects of their designs were the most successful?
• What do we mean by a strength-to-weight ratio?
• How did your designs change throughout the engineering design process?
• What did you learn from testing?
• How were you frugal with your building supplies to lower weight without sacrificing strength?
• Looking back, how did your initial designs differ from your later designs?
• What effective design techniques were developed and widely adopted?
• What is the benefit from doing many design iterations? (Improving the design!)
• If you kept working on your design, what changes would you make to further improve your tower?
• How do these further changes relate to the engineering design process?

Post-Activity Assessment

Tower Review: Administer the three-question Strongest Strongholds Assessment, a PowerPoint® file, to assess if students understand how forces can be better distributed across a tower structure.

Troubleshooting Tips

Students often use much more tape than is necessary. Tape usage can be reduced (and hence, weight reduction) by splitting the tape in half, length-wise, or by using a technique to thread straws into one another. To thread the straws: pinch the tip of a straw and then fold it to reduce its diameter, then slip the straw into another straw. See if students discover such techniques—or show them how—depending on how challenging you want the activity to be.

Additional Multimedia Support

As part of their design research, have students observe examples of straw tower designs by watching some of the many YouTube videos on the topic. For example nine different tower designs are tested to failure in the Engineering Straw Tower Project – Period 1 (7:20 minutes) at https://www.youtube.com/watch?v=mZREsrdvxYM.

Copyright

Contributors

Supporting Program

Acknowledgements

The contents of this digital library curriculum were developed by the Renewable Energy Systems Opportunity for Unified Research Collaboration and Education (RESOURCE) project in the College of Engineering under National Science Foundation GK-12 grant no. DGE 0948021. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.

Many thanks to Travis Smith and the University of California Davis RESOURCE Program for the tremendous support they provided in developing, testing and refining this activity.