Build a Cantilever

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.

Supplies Needed:

 - Flexible and Straight Straws

 - Masking Tape

 - Dixie Cups

 - Pennies

 - Ruler or tape measure

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

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

   How to win:

    1. Maximum length, and most weight

    2. Minimum width, and most weight

    3. Most weight

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?

About the Presenters

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Jennifer Malloy

Jennifer Malloy obtained a Bachelor of Science degree in Civil Engineering from South Dakota School of Mines and Technology in Rapid City, SD. 

 

During college she interned every summer as a land surveyor.  Jennifer moved to Bismarck, ND after graduating from college to begin her career as a Civil Engineer. 

 

She has 14 years of experience and is a Project Manager at Apex Engineering Group in the Water Resource sector, a Certified Floodplain Manager, and Land Surveyor in Training. 

 

Jennifer is married with four children and a dog named Rocket.  

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Sarah Mohl

Sarah Mohl attended NDSCS and graduated in 2004 with AAS Architectural Drafting and Estimating and in 2005 AAS Construction Management.

 

Sarah has 15 Years of experience as a Civil Engineering Technician and works for Apex Engineering Group in the Bismarck office. Her time has been spent primarily within the Transportation sector as a CADD technician for Engineers and Designers.

 

She is a busy mother of four who enjoys volleyball, spending time outdoors and watching her kids sporting activities.

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