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.
- Flexible and Straight Straws
- Masking Tape
- Dixie Cups
- Ruler or tape measure
- 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
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.
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
- 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
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.
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.