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In this multidisciplinary lesson, students use K’NEX to Design and Build a Bridge


Science, Social Studies  


5, 6, 7, 8  

Title – Bridges
By – K’NEX Education
Primary Subject – Science
Secondary Subjects – Social Studies
Grade Level – 5-8

The Bridge: How Much and When?
How Much Will It Cost
And When Will It Be Done?
Understanding the Logistics Involved in Building a Bridge

Objectives – Students will:

  • Calculate the costs of the materials they need for building a model bridge
  • Control cost variables when designing a bridge


  • K’NEX
  • 3×5 cards
  • Pencils and paper
  • Pre-measured weights in 2-3 lb. increments (.91-1.36 kg)
  • Portfolio

Duration – 120 Minutes

Concept Development:
Bridge builders not only have to consider the location and function of a bridge, but also its cost and the timetable for building it. Although they cannot skimp on materials because of a potential loss of safety, they must keep within budget. Keeping on schedule is important too, since people will need to use the completed bridge, and the longer it takes to build the bridge, the more it will cost. Another factor to keep in mind is the fact that only certain materials may be available to the builders and this may affect how the bridge is built.

Building Activity
Divide the class into teams of four to six students and have them choose a name for their bridge design and engineering firm, e.g. the K’NEX Bridge Design & Engineering Firm. Each team is competing for the Hometown River bridge building job.
The Challenge: Build a K’NEX bridge model that crosses the one-foot-wide (30.5 cm) Hometown River. Three-inch-tall (8 cm) boats must be able to pass under the bridge, and the bridge must be able to hold up at least three pounds (1.36 kg) of weight. Do you think you can do it?

Tricks to earn the job
Tell the students: “Each group must work effectively as a team to build a K’NEX bridge model at the lowest cost and within 45 minutes ! If you meet the challenge and accomplish this, your design firm will get the job to build the actual Hometown Bridge! Work in groups, make joint decisions and help each other get the work completed on time!”
Copy this chart on the chalkboard and / or copy it for your students and instruct students to use it to calculate their costs. Allow them time to discuss and design their bridge. Then, start a timer for 45 minutes of building time.

Allow each group to test its bridge to make sure it can support at least three pounds (1.36 kilograms). You might have them rest books previously weighed in pound or kilogram increments [8 ounces to 1lb. (.227 – .45 kg.)] on the bridge or suspend them below the bridge. Check the costs and finish times for each group and award the bridge building “contract” to the firm that meets all the requirements for budget, time, and bridge strength and works together effectively as a group!
You might prepare an official-looking but humorous document to use for the “contract”.

1. Investigate famous bridges and bridges from other cultures to find out how long each took to build. Discuss the information collected.
2. Have students use their portfolios as log books to keep track of their materials and their costs. Students might organize their information in chart form, listing the types of pieces they used, the unit cost for each type, the number of each type used, the total cost for each type, and the total cost for the bridge. For students who may need assistance with this or who may be unable to do these calculations, have students count the number of K’NEX pieces used rather than the cost amounts assigned to them.

Check each groups’ calculations to make sure they tallied their costs correctly. Look for their bridges to include the structural parts of bridges that they have already learned about and for their designs to meet the stated requirements. Also, monitor the cooperative teamwork of each group to make sure that each group member has a chance to contribute to the bridge design and construction.

Clean Up
Allow 5-10 minutes for students to unsnap and sort the K’NEX pieces, and return them to the building stations.


  • The Brooklyn Bridge spans the East River between New York City and Brooklyn, New York. It was completed in 1883 at a cost of $15.5 million, more than twice as much as its first estimate.
    Its designer thought the bridge would take five years to build, but it took almost fourteen years. It is rare that a bridge is actually completed on time or on budget! Still, the bridge was acclaimed as an engineering wonder. The people of New York celebrated its opening with music, speeches, warships firing a salute, a visit from President Chester A. Arthur, and 14 tons of fireworks, which lit up the sky over the bridge for an hour!
    Investigate the building of the Brooklyn Bridge and discuss the reasons for the prolonged building time. What could have been done differently to save time and money?
  • Worksheet: The Cause…Way
  • Suggested reading on bridges and bridge building, particularly for the Brooklyn Bridge.

The Cause…Way

You are the mayor of your town, Mitowne, USA. The residents who elected you are angry because the town needs a new bridge to cross the Mitowne Snake River. The town does not have the money from taxes to pay for the bridge, and attempts to raise the money from local businesses have failed. There is an upcoming election in the fall and you want very much to be reelected as Mitowne mayor. Your must find money to build the bridge Mitowne so desperately needs. Your last chance is to lobby before your state government and
convince them to allocate the funds for the bridge reconstruction. Write a persuasive and convincing speech to accomplish the goal – Mitowne will get its bridge and you will be reelected!

You must address the following points in your speech.

  • Why the bridge must be replaced
  • Why the bridge is crucial to Mitowne
  • How much the bridge will cost
  • How long it will take to build
  • What will happen if the bridge isn’t rebuilt
  • How the bridge is used most
  • Alternatives if the bridge isn’t built
  • What material you propose to build the bridge from
  • What the bridge should look like
  • Why the bridge appearance is important or unimportant

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