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Stage 2 – STEM Activity 12

Build a bridge

Photo showing a half built Sydney Harbour Bridge shown across Sydney Harbour. The upper arch is in 2 parts and has not yet met in the middle. The roadway has not yet been added. The triangles that make up the arch are clearly visible.

Description of activity

Students design and construct a bridge using a variety of materials to carry a given mass. They will incorporate knowledge about shapes into their design to build strong structures.
This activity takes approximately 2 hours for:

  • research and design
  • construction, testing and evaluation.

Context

Students would have played with building blocks and made simple structures. They would have discussed the rigidity of shapes.

Outcomes

Skills

ST2-4WS investigates their questions and predictions by analysing collected data, suggesting explanations for their findings, and communicating and reflecting on the processes undertaken
ST2-5WT applies a design process and uses a range of tools, equipment, materials and techniques to produce solutions that address specific design criteria
MA2-2WM selects and uses appropriate mental or written strategies, or technology, to solve problems
MA2-3WM checks the accuracy of a statement and explains the reasoning used

Knowledge and understanding

ST2-7PW describes everyday interactions between objects that result from contact and non-contact forces
ST2-13MW identifies the physical properties of natural and processed materials, and how these properties influence their use
ST2-14BE describes how people interact within built environments and the factors considered in their design and construction
ST2-16P describes how products are designed and produced, and the ways people use them
MA2-6NA uses mental and informal written strategies for multiplication and division
MA2-8NA generalises properties of odd and even numbers, generates number patterns, and completes simple number sentences by calculating missing values
MA2-15MG manipulates, identifies and sketches two-dimensional shapes, including special quadrilaterals, and describes their features
MA2-16MG identifies, describes, compares and classifies angles
VAS2.3 uses the forms to suggest the qualities of subject matter

Resources

  • Geostrips, paddle-pop sticks, paper, boxes, wooden blocks, books, cardboard, straws, pipe cleaners, sticky tape
  • Coins or masses

Work, health and safety

  • Check relevant Work, health and safety guidelines.
  • Ensure all items brought in from home are clean and safe to use.

Evidence of work for assessment purposes

  • Labelled sketch of a bridge showing notes on shapes, rigidity and materials used
  • Working showing how the quantity of materials needed was calculated
  • Photo of the constructed bridge
  • Notes regarding the weight-bearing ability of the structure.

STEM teaching and learning activities

  • Students take photographs of local bridges and observe pictures of different types and well-known bridges.
  • Students discuss and write responses to the following questions:
    • What is the main purpose of a bridge?
    • Where do you find bridges?
    • What are bridges made of?
    • What makes a good bridge?
  • What types of bridges are there? Sketch and identify some different types.
  • Discuss the different shapes seen in bridges, eg triangles, arches, squares. Discuss the rigidity of these shapes.
  • Students test the rigidity of the different shapes using geostrips. By constructing, describing and drawing the shapes, students apply different forces to the shapes and note their findings.
  • Students discuss the number patterns that emerge depending on the shapes that they tested.
  • Challenge students to design and construct their own bridges from a variety of supplied materials. They will test the success of their design by placing a certain number of masses on it to see how much weight their bridge can take without collapsing.
  • From their design, students determine the types and amount of materials they will need, for example if the bridge design is based on triangles, students can calculate the number of paddle-pop sticks they will need.
  • Students carry out a design plan to construct their bridge.
  • Once students have constructed their bridge they test the strength by placing masses on it. Challenge students to think how they can make any changes to their bridge so that it can hold more weight. Students consider the forces applied to the bridge and how the following factors may affect their distribution:
    • shapes used in the structure
    • materials used.
  • Students display their bridges to the class. They discuss how they made their bridge and the weight their bridge can hold without collapsing. Students also discuss whether or not they made any changes to their initial design after testing it.
  • Students provide constructive feedback and discuss the following questions:
    • Which shapes provided the strongest support?
    • How can this be explained?
    • Which materials were the most useful?
    • What was it about these materials that made them useful?

Vocabulary list

Arch – a curved symmetrical structure spanning an opening and typically supporting the weight of a bridge, roof, or wall above it
Bridge – a structure that spans and area, eg a river, gorge, roadway
Deck – the main horizontal platform of a bridge
Geostrips – strips used to make geometric shapes
Rigidity – stiff and not flexible
Suspension bridge – a bridge that is hung from two or more cables that are held up by towers

Key inquiry questions

What materials are best used in designing a structure?
Students will discover that the materials used in designing their bridge should be strong and durable. They may also learn that by using a certain material in a different way (folding a piece of paper to make it thicker) will make the paper stronger and enable it to hold more weight.

How do the shapes used in construction affect the strength of the bridge?
The material from which a structure is made is important but you can strengthen a material by changing its shape. Engineers often use different shapes, eg arches and triangles. The curve of the arch spreads its load on the bridge and makes it stronger.

Triangles are strong shapes used to support structures. Under a heavy load, a square distorts easily and ends up looking like a parallelogram. If you put a brace on diagonally across a quadrilateral, you create two triangles and a much stronger shape that cannot be deformed without changing the length of one of its sides. The triangle is an extremely popular building shape because it is not easily deformed.

Additional information

Basic information about bridges for teachers
A bridge spanning a river, valley, sea, or road needs deck to be strongly supported, since it has no support directly beneath it. The longer the bridge, the more it weighs, the more it carries, and the bigger the risk it will collapse. Bridges certainly do fall down from time to time, and quite spectacularly, but most stand happily still for years, decades, or even centuries. They do it by carefully balancing two main kinds of forces called compression (a pushing or squeezing force, acting inward) and tension (a pulling or stretching force, acting outward), channelling the load (the total weight of the bridge and the things it carries) onto abutments (the supports at either side) and piers (one or more supports in the middle). Although there are many kinds of bridges, virtually all of them work by balancing compressive forces in some places with tensile forces elsewhere, so there's no overall force to cause motion and do damage.

Different cross-sections of construction materials will also affect the rigidity of a structure, eg tube structure vs a rod or angled support vs a flat support.

The following statements outline some common preconceived ideas that many students hold, which are scientifically inaccurate and may impede student understanding.

Materials are the only important factor considered when designing structures
The material from which a structure is made is important but you can strengthen the material by changing its shape. Bridge designers often use different shapes, eg arches and triangles. Triangles are a rigid shape and the curve of an arch spreads the load on the bridge and makes it stronger.

Support materials

Teacher resources

Student resources

Student interactives

Diversity of learners

For additional support

  • Students may complete their design task in groups or independently.

For extension

  • The types and/or amount of material are limited or specific weight bearing is determined.
  • Students research the history of a famous bridge, eg Sydney Harbour Bridge.
  • Investigate the importance of balancing the compression and tension forces in bridge design.
  • Students go on an excursion to view, sketch and identify the components of a local bridge.

Review

In this STEM activity, your students selected a variety of materials to design and construct a bridge. They have investigated the strength of shapes and considered the forces and applied this knowledge to their design. The understandings of forces, characteristics of materials and structure and function are enhanced in Science Stages 4 and 5 and the basis of all senior science studies.

Students have tested their design and used problem-solving strategies to improve the performance of their bridge. The ability to develop and implement a design plan is an essential skill, more fully developed in Technology (Mandatory) Stage 4.

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