Build suspension bridges out of sticks, twine and homemade wooden pegs based on a double cantilever (the two halves of the bridge stand independently).


Problem-solving. Identifying the practical and technical issues and finding solutions as a team.

Understand how suspension bridges and cantilevers work. How are the forces transmitted to the anchor points? Practical. Building a working suspension bridge capable of carrying 5kg at the centre of the span. Science, Design & Technology – Forces involved in a loaded suspension bridge. Solving the design problems involved in making a suspension bridge.

Per bridge or group – 18 x 1mtr sticks, pointed at one end per bridge, ball of twine, 8 steel tent pegs, scissors, suspension bridge diagrams, 2 mallets, 5 kg weight.

  1. Explore the pre-constructed bridge or cantilever. What is the nature of the forces involved? Where are the forces going? Study how the cable distributes the forces.
  2. Explain the parts of a suspension bridge – the towers, main cable, suspender cables, deck/roadway, anchors.
  3. Demonstrate working techniques and explain the importance of checking all anchor points – the bridge is only as strong as its weakest link.
  4. Make the Bridges. Divide into groups and allow 45 – 60 minutes to complete the task.
  5. Test the bridges with a 5 kilo load. Discuss the outcomes. If a bridge fails – why?
  6. Discuss other structures that use the same principles– for example, cranes and modern buildings. Demonstrate how the same technique can be used to make a shelter.

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