Mind the Gap

Marshmallows with blue dots…an activity that gets the message across

Contributed by: Gordon Webb

Grade 7: Structures and Mechanisms

  • Structures have a purpose.
  • The form of a structure is dependent on its function.

Inquiry Skills Used

Initiating & Planning: brainstorming

Performing & Recording: drawing the design of the bridge

Analyzing and Interpreting: testing the soundness of the structure and drawing conclusions based on information gathered

Communicating: visual, written and oral communication

Safety Considerations

Students should be careful when handling sharp toothpicks.


Engineers are people who design and make things.  Structural engineers design, build, and test things that have to do with structures. They often research various shapes for their designs, as well as the interrelationships between these shapes and the integrity of the structure.  They must also assess how various materials will function to make the structure more sound.  In the designing stage, engineers consider several things: the task (what they are being asked to build), the parameters and size of the structure (how long/strong/tall it must be), and can the structure be built in a cost effective way (cost/durability of the materials being used).

What You Need

  • Toothpicks
  • Miniature marshmallows
  • 5 quarters in a paper cup
  • Round tipped scissors
  • Paper and pencils
  • 2 chairs
  • Erasers and rulers

What to Do

  1. The students will be building a bridge to cross a gap.
  2. The design must be at least 30 cm long and must hold a container holding a specified weight.
  3. Set up chairs 30 cm apart from each other.
  4. Students are directed to create a bridge that must bridge the gap between chairs.
  5. Brainstorm about concepts of good engineering practices: understand the problem, design, build a model, and test.
  6. Discuss the types of problems that could be encountered during this exercise.
  7. Explain to students that they will be using the engineering cycle to build their bridges.
  8. Explain the challenge and the expectations of the outcome.

Summary Notes

All engineers use similar processes to resolve a given problem. The steps in the process are as follows:

1.) Understand the Problem:  they first must make sure they understand the problem or challenge.

2.) Design a Solution: draw a design of their resolution to the problem on paper.

– consider things such as the parameters of the task

– materials to use

– cost of materials.

3.) Build a Model: build a model (a smaller version) of the project to test it and see if it works.

4.) Test & Retest: test the models and assess.  They may need to redesign and fix any inadequacy.

5.) Repeat.

Where to Go from Here?

Any materials can be used. A larger structure could be constructed using dollar store meat skews and hot glue guns. The students could build suspension bridges with string and popsicle sticks. The students could be challenged to make a larger structure using different materials.    The students could explore the effects of outside forces acting on the bridge (e.g., wind, earthquakes, expansion and contraction from changes in temperature).

STSE Links

How might this information influence the design and appearance of a structure, the materials it is made from, and so on? What things might a company need to take into account when considering the construction of a new structure that consumers might not consider (e.g., the environmental impact of using certain resources to make the structure, the eventual disposal of the structure)?

Write a newspaper article that identifies the factors that caused a structure to fail and the impact it might have to the human and natural environment.

Cross Curricular Connections


  • Write the design plans for a structure that will support a given load.  Include labelled diagrams, materials list, and procedural instructions.  Add any revisions needed to effectively design the structure.
  • Write a newspaper article that identifies the factors that caused a structure to fail and the impact it might have to the human and natural environment.



  • Design, construct, and use physical models to investigate the effects of various forces on structures (Number Sense and Numeration: ratio, Measurement: scale drawings, etc.).
  • Describe the role of symmetry in structures (indirectly, Geometry- reflection).

Visual Arts

  • Draw and label a diagram that shows both the external forces and internal forces acting on a structure.





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