About the Activity: 

Have you ever heard of a cantilever? Did you know that a diving board and balcony are examples of a cantilever?  A cantilever is a part of a structure that is only supported at one end.  More examples are roadway traffic signals, airplane wing and even a skyscraper and the Eiffel Tower.  Engineers use a variety of materials and techniques to make cantilevers feasible.

Stick your arm out straight to your side.  It’s a cantilever!

• What force is working to pull your arm down? (Gravity)

• How are you keeping your arm up under the force of gravity? (Muscles)

• Imagine your arm is a cantilever balcony or part of a cantilever bridge.

  • How strong would it have to be to support the weight of people and cars?

  • What would keep the balcony or bridge from ripping away from its base?

We would like you to work in groups of 2 to design and build a cantilever that hangs as far off a table as possible.  However, if you want more of a challenge you can design and build a cantilever that holds the most weight.

Participants work in teams to build a cantilever.  Encourage them to consider the force of gravity and plan a way for the table to support the weight of the cantilever.  Some teams may discover that they can fit straws together without using tape.  Some may decide to build a truss to provide strength. 

If participants are stuck or frustrated, help them by asking questions that can lead them to a solution. 

If time allows, have the participate redesign the cantilevers to make them longer or stronger.

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Supplies Needed:​

 - Flexible and Straight Straws

 - Masking Tape

 - Dixie Cups

 - Pennies

 - Ruler or tape measure

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Rules:

​ - Design and build a cantilever that hangs as far off a table as possible

 - You can use as many straws as you like but only 3 feet (or 1 meter) of masking tape

 -  The cantilever cannot sag lower than 6 inches below the tabletop

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Competition:

​ If the students want to have a friendly competition, they must put a dixie cup on top of the straw cantilever and begin filling the cup with pennies to see how much weight the cantilever can hold.

  Rules:

     1. The cantilever length must be a minimum 10 inches from the edge of your table/desk.

     2. Place the cup within 1 inch of the end of the cantilever

     3. The cup cannot be taped to the cantilever

     4. The cantilever cannot sag more than 45 degree angle

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   How to win:

    1. Maximum length, and most weight

    2. Minimum width, and most weight

    3. Most weight

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Discussion:

 - Did you see the points of failure?

 - What would you have done differently?

 - What other materials do you think you could use to make your cantilever stronger?

 - Where have you seen cantilevers in your community?​

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